Y ) (Q:) ~ OL John M. Grizzle and Wilmer A. Rogers 1,4 . v , dh I w ANATOMY and HISTOLOGY OF THE CHANEL CATFISH JOHN M. GRIZZLE, ASSISTANT PROFESSOR AND WILMER A. ROGERS, PROFESSOR Department Of Fisheries And Allied Aquacultures U.S. Department of Commerce, NOAA, National Marine Fisheries Service Commercial Fisheries Research and Devel- opment Act of 1964, Public Law 88-309, Project 2-187-R. AUBURN UNIVERSITY Agricultural Experiment Station R. Dennis Rouse, Director /Auburn, Alabama Auburn University offers its programs to all without regard to race, color, sex, or national origin. i COPYRIGHT 1976 BY AUBURN UNIVERSITY AGRICULTURAL EXPERIMENT STATION PRINTED BY AUBURN PRINTING, INC. AUBURN, ALABAMA FIRST PRINTING 2M, NOVEMBER 1976 CRAFTMASTER PRINTERS, INC. OPELIKA, ALABAMA SECOND PRINTING 2M, MARCH 1979 THIRD PRINTING IM, MARCH 1985 ii ACKNOWLEDGMENTS This study was supported in part by a grant from the U.S. Department of Commerce, NOAA, National Marine Fisheries Service Commercial Fisheries Research and Development Act of 1964, Public Law 88-309, Project 2-187-R through the Missouri Department of Conservation; in part by the USAID Fisheries program at Auburn Univer- sity; and in part by the Southeastern Cooperative Fish Disease Project which is partially funded by nine cooperating states with Dingle-Johnson sport fish restoration funds. Our thanks to those sup- porting agencies and especially to Charles Purkett, Charles Hicks, and Reed Twichell of the Missouri Department of Conservation and to I. B. Byrd of the NMFS for their support; to O. L. Green of the Southeastern Fish Cultural Laboratory, Mar- ion, Alabama for providing some of the large cat- fish specimens used in this study; and to personnel of the Department of Fisheries and Allied Aqua- cultures, Auburn University Agricultural Experi- ment Station, who assisted in collecting specimens or gave critical comment on the manuscript. We are grateful to Peter Carrington who did an out- standing job of preparing drawings. Belinda Tor- bert, laboratory technician, was especially helpful in preparation of tissue sections. Dr. John L. Gaines worked on this project initially and made important contributions before leaving to attend medical school. Thanks are also extended to Dr. Bryan Duncan for dissections of the nervous sys- tem and to Glenda Bradley, Department of Poul- try Science, for advice concerning electron micro- scopy techniques. iii CONTENTS INTRODUCTION ...... LITERATURE- -- -- -- -- -- -- -- -- -- MATERIALS AND METHODS .... EXTERNAL ANATOMY . -- BARBELS ..........-------------------------------- F IN S -- --- --- --- --- --- - --- ---- -- - LATERAL LINE -..- ---- ---- SEXUAL DIFFERENCES .-- CIRCULATORY SYSTEM --- --- ANATOMY OF ARTERIES AND VEINS -... Methods for Injection of Blood Vessels with Latex Arterial Circulation ..- Venous Circulation.. ----------------------- HISTOLOGY OF BLOOD VESSELS Arteries ----n Capillaries and Related Structures Veins - H EART ...... ..... .. ....---------- Sinus Venosus - - -- A trium ...........-- - --- ---- - Ventricle - Bulbus Arteriosus .- LYMPHATIC SYSTEM HEMOPOIETIC TISSUES - SPLEEN ... -- - - - - -- - -- - ---- ------- T HY M US.-------- -- --- - -- - -- - -- -- -- BLOOD CELLS --- Erythrocytes --- Leukocytes -- -- - - - -- - - - - - - Hematocrits - DIGESTIVE SYSTEM - - ALIMENTARY CANAL ..... Oral Cavity and Pharynx Esophagus . . . . .. . . . . . . . .. . Stomach .-- ---- Intestine ...- --- -- -- - ---*-- - ACCESSORY DIGESTIVE ORGANS Pancreas . . . . . . . . . . . . . . . . . . . L iv er - - - - - - - - - - - - - - -- - - Gall Bladder and Bile Ducts --- SWIM BLADDER -.------ ENDOCRINE SYSTEM HEAD KIDNEY -- - Interrenal T issue ---------------------- ------- Chrom affin Tissue ........- ------------------- CORPUSCLES OF STANNIUS ....................... PANCREATIC ISLETS ------------------------ ------- PITUITARY G LAND ............ ------------------- N eurohypophysis ............................. R ostal Pars D istalis .......................... C audal Pars D istalis ......................... Pars Interm edia ....... ------- ---------------- T H Y R O ID - --- --- ----- -- -- ---- ------- ----------- ULTIMOBRANCHIAL GLAND ....................... CAUDAL NEUROSECRETORY SYSTEM-- EXCRETORY SYSTEM .............................. K ID N E Y -..... - --....... . . . . . . . . . . . . . . . . . . .. . . . .. . . . . . R enal C orpuscle ------------------------ ------ Renal Tubule - OPISTHONEPHRIC DUCTS URINARY BLADDER INTEGUMENTARY SYSTEM SKIN .. ...- Epidermis Dermis ... FINS . .... AXILLARY GLANDS iv Page ~1 3 -3 5 5 5 9 9 9 10 10 10 11 11 -12 12 13 13 13 14 15 15 -15 17 19 19 19 20 21 -------------------- -------------------- -- 22 24 24 25 26 27 29 29 29 29 30 30 31 --- 31 31 32 -- 33 33 33 33 35 35 35 36 38 39 40 40 40 40 41 42 --------------------.. 5 -------------------. ................... ------------------ ---. ..................... 10 -------------------- 1 1 -------------------- 1 1 -------------------- 1 2 --------------------- 1 2 -------------------- 1 3 -------------------- 1 3 -------------------- 1 3 -------------------- 1 4 -- ----- --1 5 -------------------- 1 5 -------------------- 1 5 -------------------- 1 7 -------------------- 1 9 -- ----- --1 9 -------------------- 1 9 -------------------- 2 0 --------------------- 2 1 -------------------- 2 2 -------------------- 2 4 -------------------- 2 4 -------------------- 2 5 -------------------- 2 6 -------------------- 2 7 -------------------- 2 9 -------------------- 2 9 -------------------- 2 9 -------------------- 2 9 -------------------- 3 0 -----.-------------- 3 0 -------------------- 3 1 -------------------- 3 1 -------------------- 3 1 --------------------- 3 2 -------------------- 3 3 -------------------- 3 3 ------.-------------- 3 3 -- ----- --3 3 -------------------- 3 5 .. .... . ..3 MUSCULAR SYSTEM MYOMERES OF THE TRUNK AND TAIL_ MUSCLES OF THE FINS Anal Fin- Dorsal Fin Caudal Fin Pectoral Fin Pelvic Fin .. MUSCLES OF THE HEAD Eye Muscles Mandibular Muscles Hyoid Muscles Branchial Muscles Hypobranchial Muscles NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM Telencephalon Diencephalon Mesencephalon Cerebellum Medulla Oblongata Spinal Cord CRANIAL NERVES Olfactory (I) Optic (II) Oculomotor (III) Trochlear (IV) Trigeminal (V) Abducens (VI) Facial (VII) Acoustic (VIII) Glossopharyngeal (IX) Vagus (X) SENSE ORGANS E y e .. . . . . . . . . Olfactory Organ Taste Buds Ear Lateral-Line System REPRODUCTIVE SYSTEM MALE REPRODUCTIVE SYSTEM Anterior Region of the Testes Posterior Region of the Testes Endocrine Function of the Testes FEMALE REPRODUCTIVE SYSTEM- Oogenesis- Spent Ovaries Endocrine Function of the Ovary RESPIRATORY SYSTEM PHARYNX GILLS .. SKELETAL SYSTEM .................. S K U L L - ... .. ............. ....... Neurocranium ---------------- Branchiocranium (Visceral Skeleton)- VERTEBRAL COLUMN AND RIBS ...... Caudal Vertebrae ................. Trunk Vertebrae and Ribs Weberian Apparatus FINS Anal Fin Dorsal Fin Caudal Fin Pectoral Fin Pelvic Fin TISSUES OF THE SKELETAL SYSTEM Bone Notochord Hyaline Cartilage Pseudocartilage Gill-Filament Cartilage Chondroid LITERATURE CITED INDEX . 43 ......4 4 45 45 45 46 46 -- -- ---- -- -- --- -4 6 46 ---- --- --- ----- 4 7 47 -- --- --- --- -4 7 -- --- --- --- -4 8 -- --- --- --- -4 9 -- --- --- --- -5 0 -- --- --- --- -5 0 -- --- --- --- -5 2 -- --- --- --- -5 2 ------ ---- --- - 5 5 -- --- --- --- -5 6 _57 -- --- --- --- -5 7 -- --- - --- --- -5 7 -- --- - --- --- -5 8 -- --- --- --- -5 8 ..58 -- --- - --- --- -5 8 -- --- - --- --- -5 8 -- --- --- --- -5 8 -- --- --- --- -5 8 -- --- --- --- -5 8 -- --- --- --- -5 9 -- --- --- --- -5 9 -- --- --- --- -5 9 -- --- --- --- -5 9 ...60 61 .. .. . .. ... .. .6 2 -- --- --- --- -6 4 66 ... -.---- --- --- -- 6 6 66 67 67 67 68 .. ... ... ... .7 0 70 71 -- 71 -- 71 -- -- --- -- -- --- -7 4 -...... .... ... ... .7 4 - -- --- 74 -- -- --- -- -- --- -7 5 79 -- -- --- -- -- --- -7 9 79 82 82 82 82 83 83 83 83 83 ..... 83 83 84 84 85 . 86 91 CHAPTER ONE INTRODUCTION The channel catfish, Ictalurus punctatus (Raf- inesque), is an important commercial and sport species in the United States. It is also promising as an experimental animal because of its hardi- ness, adaptability to laboratory conditions, and availability. Culture of channel catfish for commercial pro- duction and stocking for sport fishing has led to an interest in the diseases of this species. Bacteria, viruses, parasites, nutrition, and water quality can at times lead to serious mortality or reduced growth. In order to adequately study the diseases caused by these agents, the morphology of the undiseased fish should be known. The use of channel catfish for pharmacological or physiologi- cal experiments also requires a knowledge of their morphology. The consideration of the morphology of one species or a group of closely related species is a promising way of presenting information on fish. The histology of trout has been described (Ander- son and Mitchum, 1974) and additional publica- tions dealing with single species or related species of fish seems desirable. Species which are impor- tant from an economic or research standpoint as well as those of comparative interest should be investigated. Some of the organs of the channel catfish have been described previously by other authors. In order to validate the previous descriptions and obtain photographs for this study, sections of all organs were examined and described. Previous descriptions of channel catfish or related species were often useful in making these descriptions but discrepencies were occasionally found. The genus Ictalurus (formerly Ictalurus and Amniurus) has received considerable attention from morphologists. Although taxonomically important differences exist between the species of this genus, most details of their anatomy and histology as described by previous authors are similar. The following descriptions probably apply generally to other Ictalurus spp. as well as I. punctatus. The anatomy and histology of each anatomical system is described separately. Some systems in- clude organs which, are developmentally but not functionally related. Many of the descriptions are superficial, but it is hoped that the illustrations and references cited will be useful in adding un- stated details. The figure captions often contain information in addition to that in the text. Elec- tron microscopy was used to supplement histologi- cal descriptions in a few cases. Terminology is a problem in anatomical and his- tological descriptions. In most instances, the source or sources of the terminology used is given, and alternative terms are given in parentheses. Both gross anatomy and microanatomy change as a catfish grows and ages, and the type of change and the rate of change varies depending on the organ considered. The most pronounced changes occur during growth of the juvenile. Early de- velopment of external features has been described by Mansueti and Hardy (1967), but after sexual maturity pronounced changes can occur such as the flattening and widening of the head of mature males. Unfortunately, the changes accompanying maturation have not been considered. In most cases, only the morphology of the adults or older juveniles has been described. Literature Information concerning fish morphology is avail- able in ichthyological texts and comparative anat- omy texts but most of this information is very general and often does not apply to catfish. Com- parative histology texts (Andrew, 1959; Patt and Patt, 1969) are useful sources of information con- cerning fish histology, and mammalian histology texts (Bloom and Fawcett, 1975) are useful for general histological information. The wide range of variation between fish species makes considera- tion of unrelated groups of fish difficult, although comparative fish histology is important. Relevant literature is discussed in the sections in which it is applicable; however, one series of papers is particularly noteworthy. The Proceed- ings of the Canadian Institute for 1884 contained six papers dealing with the morphology of most systems of "Amiurus catus" (Macallum, 1884; Mc- Kenzie, 1884; McMurrich, 1884a and b; Wright, 1884a and b). The descriptions of the gross anat- omy are accurate, although the terminology now in use is often different. The histological descrip- tions are sometimes inaccurate or misleading ex- cept for those of the nervous system. The species described in the above mentioned papers is prob- ably I. nebulosus according to some authors (Shel- den, 1937; Allis, 1908; Kindred, 1919), but ac- curate species identification is difficult to deter- mine from the information presented. Materials and Methods Specimens examined were obtained from ponds of the fisheries unit of the Auburn University Agricultural Experiment Station, from the South- eastern Fish Culture Laboratory, Marion, Ala., and from Lee County public lake, Lee Co., Ala. Additional specimens were examined from other sources, many being received for disease diagnosis at Auburn University by the Southeastern Coop- erative Fish Disease Project. Size of the specimens ranged from newly hatched fry to adults weighing 4 kg. Specimens smaller than 20 mm TL are not considered in most descriptions in this publication, but were useful in determining the development or overall organ- ization of some systems. Dissections were made of both fresh and for- maiin-preserved specimens for descriptions of gross anatomy. Serial sections of fingerlings were useful in determining positional relationships be- tween organs. Frozen adult specimens were cut with a band saw into sections approximately 1 cm thick in transverse and sagittal planes. Figure 29 was drawn from sketches of these frozen sections and from dissections of adult specimens. Bouin's fixative, 10 percent buffered formalin, and Helly's fixative (Humason, 1967) were used for routine histological preparations. Most tissues were embedded in paraffin, but some tissues that were difficult to section were embedded in cel- loidin. Harris' hematoxylin and eosin (H & E) and Masson's trichrome stain (Masson's) were routinely used, but several other stains were used on selected tissues. The fixative and stain are indicated for each figure. Black and white pho- tomicrographs were made with Panatomic-X film and most color photomicrographs were made with Ektachrome-X. Tissues for electron microscopy were fixed in 3 percent glutaraldehyde in phosphate buffer fol- lowed by postfixation in 1 percent osmium tetrox- ide or were fixed directly in 1 percent osmium tetroxide in phosphate buffer. Fixation was at approximately 4?C. The tissue was embedded in an epoxy-araldite mixture (Mollenhauer, 1963) and sectioned with glass knives. Sections were double stained with uranyl acetate (Watson, 1958) followed by lead citrate (Reynolds, 1963). A Philips EM 300 electron microscope was used, and electron micrographs were made with glass projector slide high contrast plates. Several methods were used only for a specific tissue or for only one system. Specialized tech- niques used include injection of blood vessels with latex, hematological techniques, dissection of mus- cles, and preparation of skeletal material. These techniques are discussed with the system in which they were used. CHAPTER TWO EXTERNAL ANATOMY The channel catfish has a variable appearance depending on the age, sex, and geographical local- ity. This variability resulted in 20 different scien- tific names being applied to the channel catfish in the early and mid-1800's when much descriptive work of fishes was done (Jordan et al., 1930). Color of the channel catfish is white to silvery on the undersides grading to a greyish slate-blue or steel-blue on the dorsum. Old specimens may be dark all over with the dorsal portion of the body being completely black. The small round to irregular dark spots on the body of young speci- mens usually are lost in large specimens. Body shape is slender and elongate with the head slightly depressed. Head length is approxi- mately one-fifth of total length (Fig. 1). Barbels Eight barbels, four dorsal and four ventral, are located around a subterminal mouth. The maxil- lary barbels (Fig. 4), which are the largest, are located dorsolaterally to the mouth and are very dark in color. The nasal barbels are located dor- sally at the anterior margins of the posterior nares. These barbels are lighter in color and about one- fifth as long as the maxillary barbels. Outer man- dibulary barbels and mental barbels (Fig. 4) are located ventrally. The ventral barbels are light to almost white in color, and are intermediate in size between the two dorsal pairs with the mandi- bulary pair being longer. Fins Immediately posterior to the head are the paired ventrolateral pectoral fins. Each of these fins has a hard ray (spine) made up of modified lepido- trichia, and nine soft rays. The posterior edge of the hard ray is serrated. The dorsal fin originates on the dorsal midline about one-third of the body length from the anterior end. A serrated spine, composed of modi- fied rays, and six soft rays make up the dorsal fin. The paired pelvic fins, comprised of eight soft rays, are located ventrolaterally immediately an- terior to the anus and urogenital openings, slight- ly anterior to body midlength. The anal fin distal margin is rounded and has 24 to 30 rays. The anal fin size, shape, and ray count is one of the main distinguishing features of channel catfish and is used to separate it from closely related species. The adipose fin is located on the dorsal midline posterior to the dorsal fin about two-thirds of the body length from the snout. The adipose fin does not have rays and is supported by fibrous connec- tive tissue. It is described histologically in Chap. 7. 7 a i 1c tc~rqo FIG. 1. Lateral view of adult channel catfish. The caudal fin is deeply forked in channel cat- fish and is another distinguishing feature of the species along with the anal fin. Lateral Line The lateral line runs longitudinally from the caudal fin to the head with cephalic lateral-line canals (Chap. 9) extending onto the head. The lateral line on the trunk and tail is located at mid- body except near the head where it arches dor- sally. It is evident by a slightly lighter color and pores opening at intervals along the length of the line. The lateral line of some specimens has branches extending dorsally away from the main line. These branches can extend into the adipose fin. Sexual Differences Sexual differentiation is possible on mature specimens using external features. The male has a distinct urogenital papilla (Fig. 2), a wide, flat head, and a darkly pigmented underbody and jaw. The female genital opening is separate from the urinary opening with small flaps covering the openings. Near spawning time the female geni- talia become swollen and inflamed. The mature female has a more slender head, a fuller body, and is much lighter colored than the male during the spawning period. Sexing of channel catfish with the use of a probe to determine if the genital and urinary ducts are separate (female) or united (male) has been suggested (lMoen, 1959; Norton et al., 1976) but is usually not necessary. S . - i i t . ol ;i U llltli il I 0 catfish. Ihe miale (right i:s a distinct urogenital papilla which is absent in the female (left). Courtesy of E. E. Prather, Au- burn University. CHAPTER THREE CIRCULATORY SYSTEM The circulatory system consists of arteries, veins, capillaries, heart, the lymphatic system, and fluids and blood cells they contain. The spleen, kidneys, and thymus are intimately associated with this system because of their involvement in the pro- duction or destruction of blood cells. A general schematic diagram of blood circulation is pre- sented in Fig. 3. Anatomy of Arteries and Veins The path of the major arteries and veins which carry blood from the heart to tissues and back to the heart can be determined most easily by inject- ing the vessels with latex. Uninjected specimens and serial sections of small specimens are useful in the study of vessels which are not easily in- jected. The branching of arteries and veins and their relationships to surrounding organs is highly variable between specimens. Only the most often encountered condition is described. The paths of the arteries and veins of the channel catfish are very similar to that described for I. nebulosus (McKenzie, 1884). METHODS FOR INJECTION OF BLOOD VESSELS WITH LATEX Liquid latex (Carolina Biological Supply) was injected into arteries and veins of anesthetized fish (gills irrigated with I percent Quinaldine) for study of their gross relationships. A 20-guage needle and 10 ml syringe were used to inject the latex into the blood vessels. Injected fish were placed in 10 percent formalin with 2 percent acetic acid to harden the latex and preserve the specimen. The caudal vein and artery were the usual sites for injection. In some specimens, these vessels were injected after removing the overlying mus- cles so that the hemal arches were exposed. The needle could then be accurately placed in the blood vessel. Injections were also accomplished by in- serting the needle parallel to the pterygiophores of the anal fin and then probing for the blood vessel. With both methods, an incision was made in the ventral body wall so that the progress of the injection could be observed. Injection of latex into other sites such as the heart or posterior car- dinal vein were usually not successful. Injection into the caudal artery results in filling all arteries except the afferent branchial arteries and ventral aorta between the heart and gills, therefore these arteries were examined without the aid of injection. Injection into the caudal vein re- suited in filling branches of the caudal vein and the hepatic portal system which receives blood directly from the caudal vein. The remaining veins were usually not filled when the caudal vein was used because renal portal system capillaries lie between the caudal vein and the posterial cardinal veins which drain the trunk kidney. In a few specimens, latex flowed from the caudal vein into the posterior cardinal vein filling all veins except the hepatic vein. This may have resulted from rupture of venules or capillaries because of ex- cessive pressure, or natural connections may exist in some specimens. ARTERIAL CIRCULATION The arterial system consists of arteries and ar- terioles which carry blood from the bulbus ar- teriosus of the heart to the capillaries of the vari- ous tissues. The blood flows from the heart to the gill lamellae where it is oxygenated before being distributed to the body. Blood pressure is reduced in the gills so that postbranchial arteries have low blood pressure compared to arteries of higher vertebrates. Branchial arteries. Blood flows from the heart to the gills through the ventral aorta. Afferent branchial arteries branch from the ventral aorta, enter each of the eight gill arches, and send a branch to each gill filament (Chap. 11) where the blood enters the gill lamellae. Blood leaves the filaments, enters the efferent branchial arteries, and flows to the dorsal side of the pharynx where the efferent branchials form the carotids and dor- sal aorta (Fig. 4). The first and second efferent branchial arteries also have branches ventral to the pharynx. A small branch from the first efferent artery goes anteriorly to the ventral hyoid region. The first and second efferent arteries contribute to the median hypo- VENTRAL AORTA PECTORAL GIRDLE / ARTERIES VEINS FIG. 3. A diagram of the major arteries and veins. External carotid artery- Internal carotid artery- Carotid sinus Coeliacorresenteric artery branchial arteries 2 'd -4 1h , artery FIGC. 4. Venutral vi ew of the effecrent bra uciial art ci ic , carotidi artei e s, an d atti or dlorsal aorita. lThe ju i ta ait( external carotid arteries branch from the irist effecrent branch ia] artcr% whic conItm i tics pottx rit-I xti to i th r ad ix otf the dotrsal aotrt a. These x essel% lie on the ventral surface of the neurocratim and %.crteh rac. ibranchial artery wxhich passcs posteriorly iithlg the ventral aorta to the hecart. The mediani hx ' vp branchial sends b~ranches to the x entral aiorta, thy roidi, and pericardial sac before becoming the coronary artery as it branches over the surf ace of' the heart. Carotid (Irteru'.s. Most of the hecad is supplied with blood iw the carotid artet ies -w hich branch from the first efferent branchial arteries dorsal to the pharynx ( Fig 4). The first eftercnt artery goes toward the midline from the gill and theil turns to run posteriorly. At this ttrni, the exteri ml carotid arises from the dorsal surface arli tile ill- ternal carotid passes directlx anteriad. The extcr- nall carotids supply the latet al portions of the heca( includling the regions of the exc e, asal capsulec. roof of the mouith, and naxillary bat~bel. The internal carotids thicken into an irreglilarkl divicded, oblong sinus ( Fig. 5 ) immediately atl tenior to its origin from the first efferent 1)ranlciaol artery. This sinus wvas thought to be a degenerate pseuidobranch by NMcKenzic ( 1884), although tiht development of this structure was not determined. The primary evidence supporting this opinion is the large artery supplying the eye wvhich arises from the sinus. This is similar to thle condition ill sonie other teleosts in) x\ Inch t he ophithalilc artery arises f101m the psetldolbraiicl ( Goodrich, 19:30). ioi e rcent stud~ies (Allis 1908 ) hav e reli teci the presenice of pselclol-anchia inltln u111s. -. A I .. . H ie iltt liii Citidt fiottx All itieiglaris di\vided siinus juist aitte riot ti- its origoi fom to le i I t efferrent brauch ial arters. Thti sintus is cuntral tot the brain, ne.ar the optic nervec 0O. Sev eral arteries (A) branch from this sinus. Trantsverse sectiont; Bouiits; It & E; X 60. The brain is supplied 1y the (ncephalic artcries which branch from the dorsal surface of the sinus formed by the internal carotid. The internal carotid continues anteriorly from the sinus to the region of the nasal cavity with b)ranches extending to lateral portions of the head. Dorsal aorta. Each radix of the dorsal aorta is formed as the most anterior efferent hranchial artery from the first gill arch turns posteriorly ( Fig. 4). The artery from the second gill arch joins the lateral dorsal aorta and then the two radices join at the mnidline to form the dorsal aorta. The ef- ferent arteries from the third and fourth gill arches join and the common vessel enters the aorta. The circulus cephalicus formed by the convergence of the radices of the dorsal aorta anterior to the gill arches in many fish species is absent. The subclavian arteries branch from the dorso- lateral sides of the dorsal aorta near the entry of the common vessel of the third and fourth arches. The subclavian arteries supply the pectoral girdle and fins. These arteries flow near the ventropos- terior margin of the ear and then laterallx to the pectoral girdle. The first ventral branch of the dorsal aorta is usuallx too small to locate except in serial sections and goes to the head kidney. The coeliacome- sentcric artery originates immediately posterior to the origin of the head kidney artery. Both of these arteries arise near the entry of the comniined third and fourth efferent branchial artery. The coeliaco- mesenteric artery supplies most of the organs of the visceral cavity. Cocliacomesent ric arter!. This artery passes be- twecn the head kidney and swim bladder after branching from the ventral side of the dorsal aorta. The first branch is the pneumatic artery which supplies the anterior portion of the swim bladder. Ventral to the swim bladder, a second branch goes to the esophagus, and then the coeliacomesenteric divides into the gastric artery and mesenteric (coeliac) artery. The gastric artery supplies most of the stomach and the mesenteric artery supplies the remaining visceral organs. The first branch of the mesenteric artery dlix ides into the cystic artery to the gall bladder and the hepatic artery going to the liver. Several anterior intestinal arteries branch from the inesenteric and supply the different regions of the pyloric in- testine. The usual number of anterior intestinal arteries is four. Posterior to the anterior intestinal arteries, a small splenic artery branches from the mesenteric. The mesenteric artery divides into right and left branihes hich conitinue posteriorly sulpplyilig the middle and rectal intestine. A genital artery branches from the left mesenteric artery and goes to the ovaries or testes. Branches of the }post'rior dorsal aorta. The trunk kidney receives blood from three or four pairs of renal arteries which branch from the dorsal aorta. The anterior renal arteries arise from the aorta dorsal to the swim bladder anterior to the kidney and loop posteriorly to the kidney. The posterior renal arteries are short and proceed directly to the kidney. Other branches of the aorta in the posterior blod cavity are the iliac arteries supply- ing the pelvic girdles and fins and the paired urinary (hypogastric) arteries supplying the uri- nary lbladder. Caudal and segm(ental arteries. The caudal ar- tery is formed from the dorsal aorta as it leaes the body cavity and enters the tail. The caudal artery is enclosed by the hemal arches of the verte)rae ( Fig 6) and is dorsal to the caudal vein which is also enclosed by the hemal arches. Seg- mental arteries branch from the dorsal aorta and V.WO f p " I V FIG. 6. The caudal artery (A) and caudal vien (V) are pro- tected by the hermal arches (H) of the vertebrae. Transverse section; Bouin's; II & E; X 173. n caudal artery at regular intervals to supply the muscle and skin of the body and tail. These seg- mental arteries are somewhat reduced in number compared to the number of vertebrae or myomeres with one segmental artery occasionally supplying several myomeres. VENOUS CIRCULATION Blood returns to the heart from capillaries through venules and veins. Two portal systems are present in which blood returning to the heart passes through an additional capillary network before reaching the heart. Renal portal system. The caudal vein is located in the hemal arches of the caudal vertebrae and enters the trunk kidney immediately upon reach- ing the body cavity. The caudal vein collects blood from segmental veins of the tail. Renal portal veins branch from the caudal vein while in the kidney and then the caudal vein proceeds an- teriorly from the ventral surface of the trunk kidney to form the hepatic portal vein. Blood from the renal portal veins and from in- tercostal veins which enter the trunk kidney from the body wall adjacent to the kidney flow through renal portal capillaries of the kidney. The blood from these capillaries is collected by the paired posterior cardinal veins. The right posterior cardi- nal is much larger than the left and both receive segmental veins from somatic muscles before en- tering the common cardinal veins. The most anterior intercostal veins enter the head kidney and form capillaries which then enter the pos- terior cardinal veins. Hepatic portal system. The caudal vein branches as it passes through the trunk kidney. Some of these branches are renal portal veins but most anastomose near the ventral surface of the kidney. The paired iliac veins from the pelvic girdle and fins join these anastomosing veins as they emerge from the kidney. The large vein formed on the ventral surface of the kidney is the hepatic portal vein which continues anteriorly to the liver. Blood from the gonads, spleen, swim bladder, and alimen- tary tract enters the hepatic portal vein. After emerging from the kidney, the hepatic portal vein passes between the gonads and re- ceives blood from numerous genital veins. A small pneumatic vein enters the hepatic portal vein just posterior to the spleen. The spleen is closely at- tached to the hepatic portal vein by extremely short splenic veins. Several intestinal veins enter the hepatic portal vein just anterior to the spleen. The gastric vein from the stomach enters near the anterior end of the hepatic portal vein. The hepatic portal vein branches before entering the liver with the branches extending to different re- gions of the liver. Within the liver, the branches of the hepatic portal vein are surrounded by pancreas (See Chap. 4) and supply blood to the hepatic sinusoids. Blood drains from the sinusoids into central veins and then into the hepatic vein which pierces the transverse septum and enters the sinus venosus. Cephalic veins. Most blood from the head enters the anterior cardinal veins. Branches enter this vein from the upper and lower jaw, operculum, pharynx, dorsolateral head, cranium, and dorsal fin. The anterior cardinal and posterior cardinal veins join to form the common cardinal vein (duct of Cuvier). The inferior jugular vein receives blood from the ventral portions of the head and then enters the common cardinal vein near the sinus venosus. The common cardinals are located in the trans- verse septum and enter the sinus venosus laterally. Histology of Blood Vessels ARTERIES The structure of channel catfish arteries varies, depending on the location of the artery. A tunica intima, tunica media, and tunica adventitia are generally present but are often not distinct. The tunica intima lines the vessel and consists of a layer of simple squamous epithelium (endothelium) and sometimes a thin layer of fibrous connective tissue. The tunica media varies greatly but generally con- sists of elastic connective tissue and smooth mus- cle. The tunica adventitia is the outermost layer and is composed of fibrous connective tissue which merges with surrounding tissue. The ventral aorta and afferent branchial arteries (Fig. 7) are elastic arteries with a tunica media composed primarily of elastic fibers which absorb some of the pressure shock resulting from ventri- cular systole. Smooth muscle fibers are also pres- ent in the tunica media. The tunica intima is composed of prominent endothelial cells and a very thin connective tissue layer. The tunica ad- ventitia is composed of loose connective tissue which merges with adjacent tissues including un- encapsulated thyroid follicles. The dorsal aorta, especially in the area dorsal to the swim bladder (Fig. 8), is slightly modified. Most of the wall is composed of collagen fibers, and a dorsomedial projection protrudes into the vessel. The tunica intima and tunica adventitia are thin compared to the tunica media. A -~ 4;' T *~ .5 5.' 'N qr F~IG. 7. The afiereiit branchial arteries (B) branch from the ecn ral a(;rta (V) just anterior to the heart. These vessels are elastic arteries andl are surrounded by thyroid follicles (T). Transverse section of :30 unm T1, juvenile; Bouin's; Ii & E; 160. I 1(;. S. 'I lie dlorsal aorta. dorsal to the swSimi bladder, has very thini t ui ua iiitiia and tutn ica ad e nti ti a and a thick tunic a miedi a (M ) U in posed enutirel]\ of c ollhigeni fibers. Thle aorta is I ocat et init grosve ini tli e srte rae soi thfat bonie (B) part ially su rroiiunds it. A project inn of thle dlorsal \N all (P') inito th lie meli is liaracteu istic oif the dorsal aorta and in sonic regions this projectioii al most coinpie telN dii hes tlie I omen. Bouin's; 11 & - 120. The remnaininog large ;irtet ics are inuscular arteries Fi'g. 9) wxith a ttmica mfedlia composed largely of smooth muscle. The ttmica itiia uisually has anl internal elastic memibrane in addition to the endlotheliuim. The tunica ad\ emtitia is thicker thaii in other tx 'pes of arteries, and consists of contnec- tiv e tissue atnd scatteredl longitudinally orienlted muscle fibers. Arterioles ate the smallest arteries and1 hav e rela- tix clv simple structure. All three lav ers are thiti and not easily dis tingttished( hy light microscopy but are clearly seen in) electron tmicrographs (Kre- mnettz andl Chapmnam 197.5). The endothelial cells are often promtinent wxith the inuclei protruding into the lumien. CAPILLARIES AND RELAED STRUCTURES Capillaries are tube shaped with the wxall one cell thick. Most tissues receiv e their b)100d supply fromt capillaries. Some organs suich as the liver at 1( spleen do not hav e distinct capillaries wxith definite boundaries; instead, they have sinusoids which v ary it shape and sometimes have no en- (lothelial cells separating the sinuisoidlal space from the surrounding tissue. The terminal blood( v.essels of the gill lamiellae aire also tiot ty pical capillaries b)ecause of their shape andl the nature of the cells lining them. These vessels are dlescibedl in Chapter 11. Some teleosts have retia miralbilia consisting of capillary b~eds with 1)100( flow of adjacent vessels being antipat allel. These structures are usually associatecl with the gas gland~ of the swimi bladlder, choroid of the eye, or certain muscles ( Lagler et al., 1962) * Structures of this type have not been dlescrilbed in channel catfish. VEINS Veins have thinner walls and larger diameters than the correspondling arteries ( Fig. 10) . The lay ers of the wall are not distinct. The endo- thliltin of the tunica intimia is present and the remainder of the wvall is composed of fibrous con- nectiv e tissue. Valves are not present inl any of the veins. Heart The heart consists of four chamb~ers; sinuis x entis, atium, ventricle, andi lbtlbus arteriosus (Fig. 11 and 12). The heart is located v entral to the p)harynx and just anterior to the liver. It is pro- tectedl v.entrally by the heavy pectoral girdle. The / 1~t A.A I- W. 9. Muscular arteries have an elastic mecmbrane which stains (larklN inl the tunica intimia, a tunica media (MI) composed priiiiarib% of smiooth mtuscle, and a relatively thick tunica ad- euititia (A)( composed primarily of light staining connectiv e tis- sitc whichlilhas longitudinally oirienitedl smooth muscle. Helly's; aldehs de tuichsin triebroine (Eppile, 1967); X 600. rs~ I -, FIG. 10. An artery (A) has a thicker wall and smaller lumen than a vein (V) serving the same tissue. These vessels are in the dorsal wall of the swim bl , Bouin's: 1 & ': , 650. SINUS VENOSUS The sinus venosus is extremely thin walled and almost devoid of cardiac muscle (Fig. 14). Most of the wall is composed of the epicardium and an inner layer of endothelium, the endocardium. Isolated fibers of cardiac muscle and nmelanin are located between the epicardium and endocardium. The sinus venosus is closely associated with the transverse septum which separates the pericardial cavity from the visceral cavity. The hepatic and common cardinal veins pass through the trans- verse septum before entering the posterior and lateral portions of the sinus venosus. The sinus venosus is sometimes difficult to distinguish in dis- sections of small fish. ATRIUM The atrium lies anterior to the sinus venosus and dorsal to the ventricle. The wall of this cham- ber (Fig. 15) is thin but has much more cardiac V~ FIG. 11. This ventral view of the heart illustrates the rela- tionship between the heart and gills (G). S, sinus venosus; A, atrium; V, ventricle; B, bulbus arteriosus. chambers are separated by paired semi-lnmar valves. The heart is located in the pericardial sac which is lined by a serous membrane. The surface of the heart is covered by the epicardium consisting of pericardial mesothelium and sparse connective tissue. Blood vessels are located between the epicardium and the underlying cardiac muscle, especially in the ventricle. Cardiac muscle (Fig. 13) of channel catfish is like that of other vertebrates. Striations, branch- ing of muscle fibers, and nuclei located in the center of fibers distinguish cardiac muscle from smooth or skeletal muscle. Many fibers of cardiac muscle are separated from adjacent muscle fibers and are covered by the endothelium which lines the heart. Nuclei of the endothelial cells are often seen on the outer edges of fibers giving an appearance of peripherally located nuclei. How- ever, the endothelial nuclei can be distinguished by their flattened profile. FIG. 12. The four chambers of the heart and its location are seen in this sagittal section of a 7-day old fry. S, sinus venosus; A, atrium; V, ventricle; B, bulbus arteriosus; T, tranverse se)p- turn; L, liver; E, esophagus. Bouin's; II & E; X 60. '4,, I *0 FIC. 13. Cardiac muscle fibers are found isolated in the spongy layer of the ventricle. These fibers have weak striations, branch, and have centrally located nuclei. Blood cells are scat- tered around the muscle fibers. Bouin's; H & E; X 600. '4 S" A, le - FIG. 14. The sinus venosus has a very thin wall composed primarily of connective tissue. Melanin (M) and cardiac muscle are scattered. Blood cells (B) fill the lumen in this specimen.Bouin's; H & E; X 320. muscle than the sinus venosus. Much of the mus- cle forms a network of widely spaced muscle fibers that are bathed by the blood contained within the chamber. The endocardium surrounds each of these fibers as well as covering the inner surface of the wall. The thin wall of the atrium is com- posed of cardiac muscle covered by epicardium. VENTRICLE The ventricle is responsible for almost all of the pumping action of the heart, and most of the cardiac muscle is in this chamber. It is located ventral to the antrium, and the bulbus arteriosus continues anteriorly from it. This is the most conspicuous chamber upon gross dissections. The thick wall (Fig. 16) has two layers of car- diac muscle, an outer copact layer and an inner '5A . spongy layer. The spong laver is much thi cker sthan the sinuscompact laver and iss composedh of widely cle forms a network of widel spaced muscle fibers which are bathed by the C, *P 4. 4 r- i * .7, (4,I' B V.. 4, * *4 .r., 5, FIG. 16. The wall of the ventricle has compact (C) and spongy (S) layers. Both are composed of cardiac muscle, but the muscle fibers of the spongy layer are widely spaced with blood flowing between fibers. Bouin's; II & E; X 240. blood in the lumen. The fibers of the spongy layer anastomose resulting in a loose arrangement of the cardiac muscle. The compact cortical layer is composed of tightly packed muscle fibers and is supplied with blood from the coronary artery. The endocardial endothelium surrounds each muscle fiber of the spongy layer and covers the inner surface of the compact layer as it does in the atrium. The epicardium covers the outer sur- face. BULBUS ARTERIOSUS This chamber has a thick wall composed of fibrous connective tissue and smooth muscle ( Fig. 17). Cardiac muscle is totally absent from the bulbus arteriosus and elastic fibers are abundant. The endothelium has rounded nuclei protruding into the lumen, and epicardium covers the outer surface. The bulbus arteriosus becomes the ven- tral aorta as it leaves the pericardial cavity. ' - i ) N - *Tak *.I*4. - ~ v~$t :~V ~ - FIG. 15. The atrium (A) has a very thin wall composed pri- marily of cardiac muscle. Isolated muscle fibers (M) are found in the lumen. V, ventricle. Bouin's; H & E; X 240. 4. i FIG. 17. The bulbus arteriosus (B) is separated from the ventricle (V) by semilunar valves (S). The wall of the bulbus arteriosus is composed of connective tissue fibers and smooth muscle. Longitudinal section; formalin; 1 & E; X 33. M V DL>c r B 7I '4. - ! The bulbus arterios is is\ ery important in er ll- lating the pressure of the blood leaving the heait (Licht and Harris, 1973). The elastic fibers allow this chamber to expand during the high pressure of ventricular systole protecting the delicate ves- sels of the gill lamellac from excessive distention. During diastole the elastic fibers shorten so that the bulbus contracts and forces blood into the ventral aorta resulting in more even pressure. Lymphatic System Teleosts have lymph vessels which originate as blind capillaries in tissues, anastomose freely form- ing larger vessels, and eventually empt\ into the venous system (Bertin, 1958a). Kremrnentz and Chapman (1975) found that the serosa of the channel catfish intestine contained numerous small and large lymph vessels. From electron micro- graphs they determined that the highly convoluted vessels had thin, flat endothelium without fenes- trations or pericytes. These vessels are similar to those of other vertebrates. Some Osteichthves including the European cat- fish (Silurus) have chambered lymph hearts lo- cated in the caudal region which pump lymph into veins (Patt and Patt, 1969). These structures were not found in channel catfish. Hemopoietic Tissues Blood formation occurs in the head kidney (Chap. 5; Fig. 54), trunk kidney (Chap. 6; Fig. 69), spleen, and perhaps the thymus. Tissue im- prints of the kidneys (Fig. 18) were made using the techniques of Ashley and Smith (1963). These imprints contain numerous hemoblasts and other immature blood cells indicating the importance of these organs in hemopoiesis. Macrophages which have engulfed erythrocytes are also present, so some blood cell destruction also occurs in these organs. Tissue imprints of the spleen indicate that it is more important in blood cell destruction and less important in hemopoiesis than the kidneys. Spleen The spleen is a dark red disk-shaped organ located between the fundic stomach and the swim bladder (Fig. 29) and is attached to the hepatic portal vein. The edges are smooth, but peripheral blood sinuses are sometimes visible grossly as protruding red spots. The surface is covered by simple squamous epithelium (mesothelium) overlying a capsule of dense fibrous connective tissues (Fig. 20). A V ~ FIG. 18. Ilcmoblasts II) are abundant in tissue imprints of the head and trunk kidnevs indicating their importance in hemopoiesis. Other immature blood cells as well as mature blood cells are also present. Macrophages (M) which have en- gulfed crthrocytces are present but much less abundant than in the spleen. lHead kidney tissue imprint; air dried; Wright- (;iemsa; X 1200. 4 ' C 4 ~i~ao "~,A I c iLa ~ 4. r; -I~ 'a FIC. 19. The spleen consists of splenic corpuscles (S) sur- rounded by red pulp (l). Large blood sinuses are located im- mnediately beneath the outer capsule and are sometimes swollen with blood (B). Bouin's; H & E: X 90. '., 4 r ItT FIG. 20. Simple squamous epithelium (E) and a connective tissue capsule (C) cover the spleen. A zone of blood sinuses (S) separates the capsule from the underlying red (R) and white (W) pulp. Bouin's; H & E; X 240. i \_c?; S 1 Ll-4-_ \.\I~hI~~L -1 FIG 2. imlesqamuseptbelium" (E n cnetv b Q! ~ a ~r 44* ~il~E3 CIC40, 4.~ to, Mr, egion of Irge blood sinuses is found b)(leatll the connective tissue, and the remainder of the organ is composed of red puiilp and splenic corpuscles containing white pulp (Fig. 19). Trabeculac are albsent and connective tissue is scarce except for arteries and veins. Young and old fish differ in the dliscreteness of the redl an(i white pulp, but the general organization of the spleen is similar. The splenic corpuscles (Fig. 21) are nodules of white pulp surrounding arteries within the spleen. The white puiilp is more basophilic than the red pulp- because its cells are more closely spaced anh there are fewer erythrocytes. In some speci- mcns a germinal center separates the artery from the \w hite pulp. and hemosiderinll is sometimes present in the splenic corpuscle. Red pulp is composed of sinusoids filled with blood. Reticular fibers form the walls of the sinus- oids which tend to be arranged circularly around the splenic corpuscles. The red pulp is more or- gamnzed and more sharply separated from white pulp in older fish. Tissue imprints ( Fig. 22) of the spleen have mature Hlood cells, minacrophages, and some im- mature blood cells. HeImohlasts are less abundant than in the head or trunk kidney indicating that the spleen is less important in hemopoiesis. Mlac- rophages often contain ervthrocvtes indicating the spleen is a site of blood cell destructionl. Pancreas is attached to the hepatic portal 'vein which lies against the spleen, and acini of exocrine pancreas are frequently found along veins within the spleen. Thvmus The thvim1s is located ii the posterior portion A A' I I(. 21 1 bhi sphi u o i < us cl has a <4 i 4., 4'4 A I~ 44, Ab( 4."* 4.4-. 4.;:" s~ . 4 .. *- , 0~n 5,~ * C- .44. '. FIC. 45. Electron mnicrograph of the liver. The bile canaliculi of the liver are formed hby the expansion of the intercellular space between hepatocytes. Nlicroxilli project from the hepato- cytes into the bile canaliculus. N1. initochondria; C, cell mem- brane; T, tight junction: I), desmosome; C, golgi complex. Osmium tetroxilde; uransl acetate and lead citrate; X 18,000. sions of intercellular spaces between hepatocy tes. Kendall and Iawkins (1975) used a staininiig technique of WVilliams (1960) to demonstrate that argyrophilic reticular fibers form a meshwork sup- porting the hepatocytes. These fibers were also in the walls of blood vessels and around the acini of exocrine pancreas surrounding the branches of the hepatic portal vein. CALL BLAI)DDER AND BILE DUCTS The gall bladder, used to store the green bile, is located on the right, posterior sitle of the liver. The common bile duct connects the gall bladder to the pyloric intestine (Fig. 46) as the intestine passes ventral to the esophagus and just posterior to the liver. Several short, small hepatic ducts FIC. 46. The common bile duct (C) connects the gall bladder (G) to the pyloric intestine (P). Hepatic ducts connect the liver (L) to the common bile duct in this area (H). Ventral view of 4 kg channel catfish. i*-- n I I .I ri, coniicet the li er to the upper portion of the coin- mon bile duct. A distinct cystic duct is not present becat sc thle htpatic ducets ienter the common hile d(tct at sexeral points begilnning at the Iteck of the FIIC. 47. The thin wall of the gall bladder has a simple col- uninar epithelium (E) which flattens to cuboidal when stretched. The miucosal epithelial cells have light staining apical portions. The remainder of the wall consists of the submnucosa (S) of fibrous connective tissue and the thin muscularis (I) which is usuall*N composel of one layer of smooth muscle. The outer SuLface is cosered by imesotheliuimi. Bouin's; II & E; X :320. 44.i 14 E ,F 4 4 V S - 9 M FIC. 48. The common bile duct, connecting the gall bladder to the intestine, has a mucosa of columnar epithelium (E) with basally located nuclei and scattered goblet cells. A submucosa (S), which forms longitudinal folds, lies between the epithelium and the muscularis (NI) composed of an irregular layer of smooth muscle. The serosa (Se) covers the outer surface. Bouin's; II & E; X 120. FIG. 49. Bile ducts (D) within the liver receive bile from bile cancaliculi. The duct has columnar epithelium and is sur- rounded by fibrous connective tissue and a few smooth muscle cells. Bouin's; H & E; X 600. gall bladder. Other authors have used different terminology for the bile ducts (Chakrabarte et al., 1973). The walls of the gall bladder (Fig. 47) and common bile duct (Fig. 48) have the basic layers found in the digestive tract, but each layer is re- FIG. 50. The pneumatic duct (P) connects the swim bladder view of 4 kg channel catfish. duced or simplified. The mucosa ha.s colulijjar epithelium with basally located nuclei. The com- mon bile duct has scattered goblet cells, and some specimens had columnar cells with a light staining apical region. The mucosal epithelium of the gall bladder flattens to cuboidal when stretched. The hepatic bile ducts in the liver (Fig. 49) which connect the bile canaliculi to the common bile duct have a columnar epithelium surrounded by fibrous connective tissue. As they approach the common bile duct and emerge from the liver, smooth muscle and serosa are added, and their structure is similar to that of the common bile duct. Swim Bladder The swim bladder (gas bladder) is physostom- ous with the pneumatic duct connecting the mid- ventral swim bladder to the dorsolateral right side of the esophagus very close to the stomach (Fig. 50). The swim bladder is located retroperitoneally just ventral to the vertebrae and between the head and trunk kidneys (Fig. 29). The walls are white and semi-rigid, and two internal septa (B) to the esophagus (E). St, stomach; Sp, spleen; L, liver. Ventral K S, '5, 4 *,~v 5, ~. ~ < 4, '- ,,,:s *~ FIG. 51. The pneumatic duct has a mucosa of simple col- umnar epithelium (E) with basally located nuclei and very light staining apical portion. A submucosa of fibrous connec- tive tissue (S) underlies the epithelium and supports tall longi- tudinal folds. The discontinuous muscularis (M) is composed of striated muscle and does not form distinct layers. The serosa (Se) has a relatively thick layer of fibrous connective tissue cov- ered by mesothelium. Bouin's; H & E; X 175. divide the swim bladder into three chambers. A transverse septum forms an anterior chamber, and a longitudinal septum extending posteriorly from the transverse septum forms two posterior cham- bers. The transverse septum is incomplete so that each posterior chamber is in communication with the anterior chamber. The anterior chamber is firmly attached to the tripodes of the Weberian ossicle series (Chap. 12). A portion of the anterior chamber is in direct contact with the skin forming a lateral cutaneous area. The swim bladder does not appear to have specialized areas for excretion or absorption of gas from the circulatory system as FIG. 52. The swim bladder wall has a tunica externa (E) and a tunica interna (I). The tunica externa is composed of two very d(ense layers of obliquely situated layers of collagen- ous fibers. The tunica interna has a thin layer of fibrous con- nective tissue and a layer of simple squamous epithelium (S) which lines the swim bladder. The epithelium has been pulled away from the connective tissue during sectioning. Bouin's; H & E; X 490. found in some teleosts (Jones and Marshall, 1953). The wall of the pneumatic duct (Fig. 51) has a mucosa of columnar epithelium, a submucosa which supports longitudinal folds, a muscularis of irregularly arranged striated muscle which does not form distinct layers, and a serosa of fibrous connective tissue covered by mesothelium. The longitudinal folds sometime form septa which divide the lumen. The mucosal epithelium has a light staining apical region and basally located nuclei. The submucosa, muscularis, and connec- tive tissue of the serosa intermingle and are often not distinct. The swim bladder wall (Fig. 52) has only two distinct layers and is almost all fibrous connective tissue. The tunica externa has two layers of fibrous connective tissue and is much thicker than the tunica interna composed of connective tissue and the simple squamous epithelium lining the lumen. The ventral surface of the swim bladder, located retroperitoneally, is covered by the parie- tal peritoneum which is loosely attached to the swim bladder. The connective tissue of the swim bladder is very dense so that good paraffin or celloidin sections are difficult to prepare. CHAPTER FIVE ENDOCRINE SYSTEM Endocrine organs have varied morphology and function but are similar by being ductless glands which depend on the circulatory system to dis- perse the hormones which they produce. Some endocrine tissues do not forn a discrete organ and may be intermingled with other tissues. The gonads contain endocrine tissue but these organs, including the endocrine portion, are described in Chap. 10. The pineal body may have an en- docrine function but is an integral part of the brain and is described in Chap. 9. The thymus, sometimes considered an endocrine organ, is im- portant in immunogenesis and is discussed in Chap. 3. Head Kidney Interrenal and chromaffin tissues are found in the head kidney. Hemopoietic tissues are also present in this organ and are discussed in Chap. 3. The head kidney is completely separate from the opisthonephric (trunk) kidney, and is composed of fused bilateral lobes located anterior to the swim bladder (Fig. 29). Kidney tubules are pres- ent in young specimens but degenerate as the fish grows and are absent in most fingerlings longer than 4 cm. The posterior cardinal vein passes through the anterior portion of the head kidney and the parietal peritoneum covers the ventral surface. The interrenal and hemopoietic tissues are intermingled throughout most of the organ but are easily distinguished in sections. INTERRENAL TISSUE The interrenal tissue (Fig. 53 and 54), also referred to as adrenal cortical tissue, is homolo- gous to the adrenal cortex of the mammalian adrenal gland (Phillips and Bellamy, 1963), and functions probably include regulation of carbohy- drate and protein metabolism, osmoregulation, blood cell movement from hemopoietic tissues, growth, regeneration, and anti-inflammatory reac- tions (Chester Jones et al., 1969). Interrenal and hemopoietic tissues are found throughout the head kidney of channel catfish. The relative abundance 4t, ) k :~ ~ *1 ~s,- %j ~ S ~ :'~ 5- ~ FIG. 53. The head kidney is primarily composed of hemopoie- tic tissue (H) and interrenal tissue (I). Kidney tubules and renal corpuscles are totally absent except in juveniles less than 40 mm TL. Bouin's; H & E; X 120. FG(,. 54. Interrenal cells (1) have a centrally located nucleus, cosinophilic cytoplasm, somewhat regular cell shape, and often appear to be arranged in cords. Hemopoietic tissue (H) has a generally more basophilic appearance due to the dark nuclei of irregularly arranged cells which often have very little cyto- plasm. Both tissue types are found surrounding blood sinuses (S). Zenker's; H & E; X 320. of these two tissue types varies widely ranging from mostly interrenal to mostly hemopoietic. The interrenal tissue is associated with venous sinuses and fits the type III distributional classification of Nandi (1962). CHROMAFFIN TISSUE The chromaffin tissue (Fig. 55) is homologous to the adrenal medulla of mammals and produces V. 5- -5 S ~ FI. 55. h a t in V*. AS, 2 4. .r r. .. FIG. 55. Chromaffin tissue (C) is found only in the wall of the posterior cardinal veins (V) of the head kidney. These large cells have centrally located nuclei and light staining cytoplasm. Some chromaffin cells have a chromaffin reaction when fixed in a potassium dichromate containing fixative but most do not. H, hemopoietic tissue. Helly's; HI & E; X 320. adrenalin and noradrenalin (Euler, 1963) which are sympathomimetic. The chromaffin tissue of channel catfish occurs in the wall of the posterior cardinal vein and its branches and can be classi- fied distributionally as type I (Nandi, 1962). The chromaffin cells sometimes have brown granules (chromaffin reaction) when fixed in potassium dichromate containing fixatives. This chromaffin reaction was not found in Clarias batrachus (Dixit, 1970). The absence of the chromaffin reaction in some chromaffin cells may be due to low content of adrenalin (Baecher, 1928). Corpuscles of Stannius The paired corpuscles of Stannius (Fig. 56 and 57) are located on the lateral edges midway be- tween the ends of the posterior or trunk kidney. Each corpuscle is spherical and occasionally mul- tilobed. The various functions which have been ,'- 5>. It i $ ~ Ed I ,$ I t~b '~." :: -~a;,31"~" ~r P kl; Z -~~1.1'----"I L r~ a 1 ",~~ i-i r i~:l) r ~ "'. . % ~* 1:$ r i I g "~ i- ~-~-" : i i " ,, :~- '~ ,. ~-lfr~ 5" ~/-~ ~: . f '~t , FIG. 56. The corpuscle of Stannius (S) is closely associated with the trunk kidney (K) and has melanophores (M) covering part of its surface. Bouin's; II & E; X 80. attributed to the corpuscle of Stannius, reviewed by Krishnamurthy (1968) and Chester Jones (1969), include osmoregulation (analogous to the zona glomerulosa of mammalian adrenal cortex), steriod production or storage, and renin produc- tion. The corpuscle of Stannius is also important in calcium metabolism (Pang, 1973). A strong rise in the calcium and fall of the phosphate level in the blood of the eel (Fontaine, 1967) and asso- ciated changes in bone tissue and mineralization of intercellular substance (Lopez, 1970) have been reported after removal of the corpuscles of Stan- nius. 4t , ~j7? .: +=~x P Ir, ;:,e 8 *r FIG. 57. The cells of the corpuscle of Stannius are arranged in cords which are separated by fibrous connective tissue septa containing capillaries. B, blood vessel. Bouin's; H & E; X 240. Pancreatic Islets The pancreatic islets (islets of Langerhan) (Fig. 41 and 42) are the endocrine portion of the pancreas and are located in the larger nodules (Brockman bodies) found in the mesenteries as- sociated with the bile ducts and anterior hepatic portal vein. These nodules of pancreas containing a large proportion of endocrine tissues are some- times referred to as "principal islets" (Gorbman and Bern, 1966) although this terminology is con- fusing (Gammon, 1970; Epple, 1969). Pancreatic islets are surrounded by exocrine pancreas and are not found in association with the pancreas found in the liver or spleen. Some of the smaller nodules of exocrine pancreas in mesenteries also have no endocrine tissue. Cell types of the pancreatic islets of the channel catfish differentiated by light microscopy include A-cells (alpha cells), B-cells (beta cells), and D-cells (Fig. 58), which have been reported in I. pInctatus (Brinn, 1971) and I. catus (Brinn, 1973). Clear cells found by Bencosme et al. (1965) in I. nebulosus may be the result of improper fixa- tion (Brinn, 1973). The A-cells are the probable r 1. * t .is s i ~ld " d* ibt -t~-~Lcg' %C # !~ , FIG. 58. The pancreatic islet has A-cells (dark pink), B-cells (blue), and D-cells (light pink). Helly's; aldehyde fuchsin tri- chrome (Epple, 1967); X 600. source of glucogen and B-cells are the source of insulin (Epple, 1969; Brinn, 1973; Epple and Lewis, 1973). The D-cells probably secrete so- matostatin (Johnson et al., 1976). An additional cell type has b)een described by electron micros- copy in I. catuts (Brinn, 1973). Pituitary Gland The pituitary (Fig. 59) is located ventral to the diencephalon of the brain (Fig. 101 and 102). The gland is composed of the neurohypophysis which develops from the brain and the adeno- hypophysis which forms from an outpocketing of the oral cavity (Wingstrand, 1966). The saccus vasculosus is located dorsoposterior to the pituitary and may be homologous to the pars nervosa of amniotes (Wingstrand, 1951). This homology has I 'jj --=~ p 7 I~ ~ i --- ri R . - FIG. 59. The pituitary is composed of the neurohypophysis (N) which extends from the diencephalon (D) into the central portion of the gland. Processes of the neurohypophysis extend into all other regions of the pituitary. The adenohypophysis has three regions. The anterior region is the rostral pars distalis (R), the middle region is the caudal pars distalis (C), and the posterior portion is the pars intermedia (I). S, saccus vasculosus. Formalin; Mallory's; X 60. N d -i . p~~- " _r d '1 ~* I~~a " not been widely accepted and the term pars ner- vosa is also used for portions of the neurohypo- physis in some teleosts (Gorbman and Bern, 1966). The saccus vasculosus is discussed in Chap. 9. NEUROHYPOPHYSIS This part of the pituitary (Fig. 59) consists of nerve fibers which extend from the diencephalon, down a short pituitary stalk, and into the dor- soanterior pituitary. The fibers within the pituitary form a neurohypophysial core with fibers extend- ing into the adenohypophysis. The neurohypophysis of teleosts has been re- viewed by Perks (1969). In the teleost species which have been studied, neurosecretory products are formed in cell bodies in the preoptic nuclei dorsal to the optic chiasma. These neurosecretorv products travel down axons to the gland. The axonal fibers are often of two types (Ball and Baker, 1969). Fibers continue into the adenohypo- physis which may be controlled by direct nervous action or by liberation of an active agent into the blood from the neurohypophysis. The close con- tact between fibers of the neurohypophysis and the cells of the adenohypophysis may explain the reduction or absence of the pituitary portal system. Possible roles of the neurohypophysis, besides con- trol of the adenohypophysis, include osmoregula- tion and control of some phases of reproduction. ROSTRAL PARS DISTALIS The pars distalis of the adenohypophysis has distinct rostral and caudal regions. The pars distalis seems to be the functional equivalent of the pars distalis of tetrapods (Ball and Baker, 1969) so this terminology is preferred to the pro- and meso-adenohypophysis terminology of Pick- ford and Atz (1957). Prolactin cells. Most of the rostral pars distalis is composed of prolactin cells (Fig. 60 and 61) arranged around prominent blood vessels. These granulated cells typically stain dark red with azocarmine or acid fuchsin although the staining reaction in Figure 60 is weak because of the fixa- tive used. The prolactin cells in channel catfish do not form the follicles found in isospondylous species (Ball and Baker, 1969) but are similar in other characteristics, particularly cell shape. Prolactin cells are the probable source of pro- lactin which is important in osmoregulation by limiting the outflow of sodium and chloride ions from the gills, although other functions of prolactin have also been hypothesized (Ball, 1969; Ball and of three hormones and each has been associated with a separate type of cell. FIG. 60. Prolactin cells of the rostral pars distalis are colum- nar cells which stain red with azocarmine and are arranged radially around veins. They have nuclei at the end of the cell opposite the vein. Bouin's; Azan; X 320. Somatotrops. These cells, also termed growth hormone cells, produce a hormone referred to as "growth hormone" (GH) or somatotropin (STH) (Ball and Baker, 1966). These relatively large cells stain orange with azan stain (Fig. 63), and are the only PAS-negative cells in the caudal pars distalis. The staining of these cells with Masson's is very similar to that of prolactin cells (Fig. 61). The growth hormone produced by somatotrops stimulates body growth, and additional actions have been suggested (Ball, 1969). Thyrotrops. These basophilic cells are intermin- gled with somatotrops in the anteriodorsal region of the caudal pars distalis and stain blue with azan. They are not easily differentiated from ?"~ #'a r I C 0 V ,i ' "8: FIG. 61. Prolactin cells stained with acid fuchsin (P) stain similarly to the somatotrops of the caudal pars distalis (C). The blue-green stained cells of the caudal pars distalis are thyro- trops. Bouin's; Masson's; X 240. Baker, 1969). The appearance of prolactin cells in some species change depending on the salinity of their environment reflecting varying demands on the organism (Schreibman et al., 1973). Adrenocorticotropic (ACTH) cells. ACTH cells (Fig. 62) form a sheet at the interface of the neurohypophysis and caudal pars distalis. These polymorphic cells are generally more spherical and basophilic than prolactin cells. ACTH cells com- prise a very small portion of the rostral pars dis- talis. Adrenocorticotropin effects the release of steroids from interrenal tissue of the head kidney (Ball and Baker, 1969). CAUDAL PARS DISTALIS The caudal pars distalis has been termed the proximal pars distalis and meso-adenohypophysis. This portion of the adenohypophysis is the source '7 5: ~ 1" i4 ~; I ,i FIG. 62. Adrenocorticotropic (ACTH) cells (center) are lo- cated in a band within the rostral pars distalis and adjacent to the caudal pars distalis (upper left). ACTHI cells are larger and more basophilic than prolactin cells. Bouin's; Azan; X 600. A A" 'A 4I r e k; " Pc" "hl X gdt _ f; ' "d t~ i, 13 " :~E~- u i I -U .. d r r ~~sn~ .Lfi ,, 6- FIG. 63. The caudal pars distalis has orange staining somato- trops and blue staining cells which are thyrotrops and gonado- trops. Bouin's; Azan; X 600. , tc " 'a "" r li;"-8h. gonadotrops during some phases of sexual matura- tion. Both cell types are PAS-positive and baso- philic. Gonadotrops are usually found ventrally and are not prominent in juveniles. Thyrotrops are the source of thyrotropin (TSH) which con- trols thyroid activity (Ball and Baker, 1969). Gonadotrops. Gonadotrops are coarsely granu- lated basophilic cells (Fig. 63) located ventrally and posteriorly in the caudal pars distalis of sex- ually mature specimens. Gonadotrops of juveniles stain lightly and are not granulated. These cells produce gonadotropin and are of two types in some species. Different types of gonadotrops have not been demonstrated in channel catfish. Only one gonadotropic hormone has been found in teleosts, and it functions in gonadal maturation and development of secondary sexual character- istics (Ball and Baker, 1969; tHoar, 1969). PARS INTERMEDIA The pars intermedia is the most posterior por- tion of the pituitary and contains more fibers of the neurohypophysis than other regions of the adeno- hypophysis. The predominent cell type stains light rect with azocarmine of azan stain (Fig. 64) or acid fuchsin of Masson's stain. A few scattered groups of cells which appear identical to gonado- trops (Fig. 64) are also present. The pars inter- media is the probable source of melanophore- stimulating hormone (NISH) which affects the distribution of pigment in melanophores and ery- throphores (Ball and Baker, 1969). FIG. 64. The pars intermedia is the most posterior part of the adenohypophysis and contains more fibers of the neurohy- poohysis than other parts of the adenohypophysis. Most of the cells are slightly acidophilic but there are patches of basophilic cells which have large granules. Bouin's; Azan; X 320. FIG. 65. Thyroid follicles are composed of a layer of epi- thelium (E) surrounding a colloid filled space. The follicles are found embhedded in loose fibrous connective tissue (C) and are not surrounded by a capsule. Bouin's; H & E; X 320. Thyroid Thyroid follicles (Fig. 65) are found along the ventral aorta and afferent branchial arteries ven- tral to the pharynx. Thyroid tissue is not en- capsulated into a distinct organ and is not grossly recognizable. Ileterotopic thyroid tissue reported in many teleosts (Baker-Cohen, 1959) has not been reported in channel catfish. The epithelium of thyroid follicles varies in height from cuboidal to squamous depending upon its activity. The colloid within the follicles is cosinophilic and is sometimes vacuolated. The thyroid produces two hormones, thyroxine and triiodothvronine which have been implicated in almost every aspect of teleost physiology (Sage, 1973). These functions can be grouped into meta- bolic effects, structural effects, and effects in the central nervous system (Gorbman, 1969). Ultimobranchial Gland These small paired glands are found in the transverse septum between the liver and heart just ventral to the esophagus. These organs are not grossly visible and are often difficult to locate. Each gland consists of cuboidal epithelium sur- rounding a lumen (Fig. 66). The ultimobranchial glands are the source of calcitonin which probably functions in regulation of calcium levels (Pang, 1973; Copp, 1969) and may be related to osmore- gulation (Pang, 1971). Caudal Neurosecretory System The spinal cord dorsal to the most posterior vertebrae has neurosecretory (Dahlgren) cells. These cells have cell bodies which are located in %N' the spinal cord near the central canal and have axons extending ventrally into the urophysis. The urophysis is a highly vascularized ventral expan- sion of the spinal cord. The neurosecretory cells are distinguished by their large size compared to adjacent neurons, polymorphic nuclei, and baso- philic cytoplasm. The caudal neurosecretory system of Ictalurus sp. (the species was not identified) was examined during a 1-year period (Cucchi, 1969). Seasonal changes in the number of neurosecretory cells or amount of neurosecretorv material were not de- tected. The development of the caudal neuro- secretory system was also considered, and it was found that a functional system was established in the third month after hatching. The function of the caudal neurosecretory sys- tem is uncertain, but most evidence indicates osmoregulation or ion balance (Bern, 1969; Ber- lind, 1973). A role in reproduction has also been indicated by the response of Cillichthys sperm duct to a urophysical factor (Berlind, 1972) and the alteration of the neurosecretory cells after injection of sex hormones into Clarias batrachus (Dixit, 1971). However, no seasonal variation in the system was found in Ictalurus sp. (Cucchi, 1969). 4 4, 4r 9 ra"r L r iebb FIG. 66. The ultimobranchial glands are located in the trans- verse septum which separates the peritoneal cavity from the pericardial cavity. Each gland has an epithelial-lined lumen (L) and numerous capillaries (C). Bouin's; H & E; X 600. CHAPTER SIX EXCRETORY SYSTEM Excretion by fish is a function of the kidney and the gills, both of which are also important in osmoregulation. The gills are described in Chap. 11 as respiratory organs. Osmoregulation in fresh- water fish consists of the kidney constantly re- moving water which enters the body through all exposed surfaces and especially the gills. Con- servation of ions by the kidney and chloride cells of the gills is also important because of the loss of ions to the hypotonic environment. Kidney The kidney of channel catfish is fused bilaterally but is divided into completely separated anterior and posterior portions (Fig. 29 and 67). The head kidney and trunk kidney of adults and juveniles over 4 cm TL are not connected by any kidney tissues or ducts. The posterior cardinal vein does pass from the trunk kidney to the head kidney. This complete separation of the head kidney was not found in any species examined by Ogawa (1961). The head kidney is located anterior to the swim bladder and is composed entirely of endocrine and hemopoietic tissue (Chap. 3 and 5). Renal cor- puscles and convoluted tubules are present in the head kidney of specimens less than 4 cm TL, but these structures and the duct which runs poster- iorly from the head kidney degenerate. The trunk kidney is located posterior to the swim bladder and extends cranially along the lat- eral margins of the swim bladder resulting in a U-shaped anterior end. The trunk kidney extends to the posterior end of the body cavity becoming more narrow posteriorly. Corpuscles of Stannius (Chap. 5) are located on the lateral margins of the trunk kidney. The trunk kidney is composed of nephrons which are the functional units of the kidney. Each nephron is composed of a renal corpuscle and a renal tubule. Hemopoietic tissue, similar to that found in the head kidney, surrounds some of the convoluted tubules and the renal corpuscles. The renal tubules are composed of various segments which have been described by Kendall and Hinton (1974). RENAL CORPUSCLE The renal corpuscle (Fig. 68, 69 and 70) is formed by a glomerulus surrounded by Bowman's capsule. Bowman's capsule is double walled with the parietal epithelium forming an outer wall and the visceral epithelium, which is in direct contact with the glomerulus, forming the inner wall. Bow- man's space occurs betwveen the parietal and vis- ceral epithelium and is continuous with the lumen of the renal tubule. FIG. 67. The head kidney (H) and trunk kidney (T) are com- pletely separate organs. The swim bladder, which has been removed from this figure, lies between the kidneys. The uri- nary bladder (U) is located in the extreme posterior portion of the body cavity. Ventral view of a 4 kg channel catfish. P, pectoral fin. :d -- ~P C F i , ~ 'V ~S Alt FIG. 68. The renal corpuscle is composed of a glomerulus and the surrounding Bowman's capsule. The glomerulus is a tuft of capillaries (C), composed of endothelial cells, which are separated from the visceral epithelium (V) of Bowman's cap- sule by the lamina densa which has stained blue. Erythrocytes are present within the capillaries. Bowman's space (S) sur- rounds the glomerulus and is enclosed by the parietal epi- thelium (P) of Bowman's capsule which has a basement mem- brane which has also stained blue. The tissue surrounding the renal corpuscle is hemopoietie tissue and renal tubules. Form- alin; Mallory's; X 600. I -, - ,, A CVt ~41N S 6, * 4~ i A FIG. 69. Bowman's space of the renal corpuscle is continuous with the neck segment (N) of the renal tubule. Hemopoietic tissue (H) surrounds most of the renal corpuscle and is much more basophilic than the renal tubules. The capillaries (C) of the glomerulus are much larger than in Fig. 68 because of the difference in fixation. Bouin's; H & E; X 470. FIG. 70. The neck segment (N) and first proximal segment (F) of a renal tubule and part of a renal corpuscle (C) are sur- rounded by hemopoietic tissue. The neck segment has ciliated, cuboidal epithelium. The epithelial cells have large, basally located nuclei and are more basophilic than other segments of the tubule. Small, dark staining nuclei (D) are located near the lumen. Bouin's; It & E; X 600. The glomerulus is a tuft of capillaries composed of endothelial cells. The visceral epithelium of Bowman's capsule is separated from the endo- thelial cells by a lamina densa (basement lamina) which is probably a fusion of the basement mem- branes of both the endothelial cells and the vis- ceral epithelium (Patt and Patt, 1969). RENAL TUBULE The renal tubules connect the renal corpuscles to collecting ducts which empty into the opis- thonephric ducts. Each renal tubule has distinct variations along its length which can be described as segments. These segments vary somewhat in length and appearance between tubules and to a greater extent between specimens. Leading from the renal corpuscle is a relatively short neck segment (Fig. 70) which has ciliated, cuboidal epithelium which is more basophilic than other segments. A sharp transition occurs between the neck segment and the first proximal segment (Fig. 71). The first proximal segment has colum- nar epithelium with a prominant striated border and basally located nuclei and is the longest seg- ment in most tubules. The first proximal segment changes gradually into the second proximal seg- ment (Fig. 72) which has lower epithelium, less prominent striated border, and epithelial nuclei located centrally or apically. An intermediate segment was described by Ken- dall and Hinton (1974) following the second proximal segment. They state that this segment S 4 *b -; o ~~, -I" :" Ib D ) b, FIG. 71. The first proximal segment of a renal tubule has columnar epithelium with large basally located nuclei. The cytoplasm is frequently more eosinophilic near the lumen. A prominent striated border is present, and small dark staining nuclei (D) are regularly arranged between epithelial cells near the lumen. Cilia extending from the neck segment are some- times seen in this segment. Transverse sections of the first proximal segment are seen in Fig. 70 and 73. Longitudinal section; Bouin's; I & E; X 600. 1 A* -4 I(. 2IG. I. The second proximal segment of a renal tubule has a smaller diameter than the first proximal segment and little or no striated border. This segment is usually the most variable in appearance. The nuclei may be near the lumen as in this section or centrally located. The staining of the cytoplasm is also variable. The small dark staining nuclei seen in the neck and first proximal segments are present but less abundant. This segment does not have a distinct beginning, and sections of tubules are frequently seen which have characteristics of both first and second proximal segments. Bouin's; H & E; X 650. may be absent from some tubules and is better differentiated by phosphotungstic acid hematoxy- lin than by H & E. The intermediate segment is similar to the neck segment by having ciliated cuboidal epithelium but has a smaller lumen and is not as basophilic as the neck segment. This seg- ment was found in some tubules of some speci- mens, but in tubules which were critically exam- ined in serial sections, it was absent more often than present. The distal segment (Fig. 73) has low columnar or cuboidal epithelial cells with eosinophilic cyto- plasm and rounded apical margin. Nuclei are usually located basally but are sometimes lo- cated centrally. Basophilic intercalated cells reach- ing from the basement membrane to the lumen and containing flattened nuclei are located be- tween the epithelial cells. This segment usually shrinks more than other segments during fixation. The collecting ducts (Fig. 74) change struc- turally between the distal segment and the opis- thonephric duct. Smaller collecting ducts have columnar epithelium surrounded by a thin layer rr * V FIG. 7:3. The distal segment (D) of a renal tubule is easily distinguished from the first proximal segment (F). The di- ameter of the distal segment is about the same as that of the second proximal segment. The nuclei of the distal segment are basally located, and the very eosinophilic cytoplasm usually shrinks resulting in space around the tubules in sections. The apical cell boundary is rounded, striated border is absent, and the lumen is usually very small. Intercalated cells with flattened nuclei are present between the epithelial cells, and round, dark staining nuclei are occasionally seen. The distal segments some- times unite before entering the collecting ducts. Bouin's; H & E; X 800. 't D A* FIGC. 74. The collecting ducts of the kidney have epithelium varying from columnar proximally to pseudostratified columnar near the opisthonephric duct. Intercalated cells, similar to those in the distal segments, are present Oiroximally. Fibrous connective tissue (F) surrounds the duct. The connectvie tissue layer is very thin near the distal segment of the convoluted tubule and becomes thick and contains smooth muscle near the opisthonephric duct. P, proximal collecting duct; D, distal col- lecting duct. Bouin's; H & E; X 320. Ilk W WVj * . CM 4- 4JX y- V11 F_ ~5..f / , :6 .>1 5'* LN- FIC. 75. This electron micrograph of a first proximal segment of a renal tubule has a small, dark staining nucleus (DN) similar to those seen in figures 70, 71, and 73. A larger, light staining nucleus (LN) seen in the basal portion of the epithelium is also present. The cell containing the dark nucleus has very little cytoplasm (C). Structures present in the epithelial cell include mito- chondria (M), lipid droplets (L), microtubules (T), and cell membrane (CM). Clutaraldehyde; Uranyl acetate and lead citrate; x 19,500. of fibrous connective tissue. The collecting ducts join together forming larger ducts before entering the opisthonephric duct. The larger ducts have pseudostratified columnar epithelium and a thick layer of connective tissue which often contains smooth muscle. All segments of the renal tubule have small, dark nuclei which are spherical or oblong and sur- rounded by very little cytoplasm (Fig. 7.5). These are most abundant in the neck and first proximal segment, often being as numerous as the larger nuclei of the tubule cells. The nuclei are often present in drawings (Edwards and Schnitter, 1933) and photographs (Hickman and Trump, 1969) of renal tubules but not discussed. Bulger and Trump (1968) suggested that these were nuclei of wandering blood cells. These nuclei are arranged regularly, especially in the first proximal segment of channel catfish (Fig. 71), indicating that these are a normal part of the tubule. The tubules of small juveniles usually have fewer small nuclei than those of adults. The nephron of the yellow bullhead, Ictalurus natalis, has been described by Hickman and Trump (1969) and is similar to the nephron of the channel catfish except for the presence of numerous eosino- philic droplets in the first proximal segment cells of the bullhead. This may be a result of a varia- tion in the physiological state of the specimens or in specimen preparation. Opisthonephric Ducts Two opisthonephric ducts (also referred to as archinephric or W\olffian ducts) course through most of the length of the kidney and continue to the urogenital pore. The urinary bladder extends anteriodorsally from its connection to the ventral side of the opisthonephric duct posterior to the kidney. The opisthonephric ducts (Fig. 76) have a pseudostratified columnar epithelial lining without goblet cells. The epithelium is surrounded by a layer of fibrous connective tissue mixed with circu- larly arranged smooth muscle. The duct posterior to the kidney has a serosa covering the outer surface. .r ~ ~~- ~n3 ^ , 9; . 0 t~ .,i~~p 1~". s~ r, ~-. ~ FIG. 76. The paired opisthonephric ducts course through most of the length of the trunk kidnes. The pseudostratified epi- thelial lining (E) is surrounded hx a thick laser o~f fibrous conl- nective tissue with intermingled sniooth muscle. Formalin; Mallory's; X 240. 4' M FIG. 78. The epithelium (E) of the urinary bladder is colum- nar when contracted and has a xerv irregular distal surface. When stretched, the epithelium is low columnar or cuboidal. A laser of connective tissue mixed with smooth muscle (MI) ies beneath the epitheliumn. Bouin's; It & E; X 600. Urinary Bladder The urinary bladder is located inl the posterior portion of the body caxvity xventral to the trunk kidney (Fig. 67 and 29). Tht wxall ( Fig. -7) of the urinary b~ladd(er is organized similarly to that of the opisthonlephric di ict . The In mciil is lift ed wxith anl epitheliuim (Fig. 78) wxhiclb is unlike that of art\ other part of the channel catfish. Tht tpi- theliel cells are columnar andi sometimes strati- fed in the relaxed bladder andl become cutboidal in the stretched bladder. The apical endis o)1 the cells are irregular resulting in an uneven surface. M ~ X .- FIG. 77. T he ss all of thic urinars bladder contains irregular bund les of smiooth miiiusclIe (M) an d jot cr1asicul ar coon eel ix tissue. T he epithieliail lining LE is soliless fiat folded %%lhen the bladder is c ontrac ted. A ecroxa (S) of fihir00 coil ietti 5e t issue and mesotfieliuon cov ers the outside. I1ellN's; 11 & E; - SO. idermi. Theeptiiu cr lag ce urni ld suusuallhaecntlylo cated double nuclei and a large svolume of eosinoiphilic cy to- plasm. Goblet cells are also present in the epithelium (of some specimens. Ilecllys s If & E; / :320. Gob~let cells andi cells w ich resemble the alarm sub~stanlce cells of the epidlermis ( Fig. 79) are preseit Iiii some spcefcies. The epitheliuim is stir- roundledl by) a layer' of coiiict ic tissue and( smoo~tth mu11scle. HI'e smlooth iuutisclt of, this lave(r ill the tiriiarv ladlder is more abundt~ant than iii the opistlioi t(phric dutct. Smiiooth imuscle fibers are orienited ci retlarl x andc longituidinially but dot not forml distincet lay ers. The external surface has at serosa of' fibrous connective tissue coveredl lx mlesotbeliu ml. CHAPTER SEVEN INTEGUMENTARY SYSTEM The integument is composed of the skin which covers all exterior surfaces of the channel catfish. Many teleosts have scales which are included in the integument, but scales are absent in catfish. Lepidotrichia develop from the integument (Goodrich, 1930) and are present as supporting elements of all the fins except the adipose fin. The skin contains unicellular glands in the epidermis, and axillary glands are present near the pectoral fin. Sense organs are located in the skin and are discussed in Chap. 9. Skin The skin (Fig. 80 and 81) is composed of the epidermis and underlying dermis. The hypodermis or subcutaneous laver lies beneath the dermis of which it is a continuation. The relative thickness of the epidermis and dermis varies in different areas of the body. The thickness of the skin in the head region is generally less than on the trunk. EPIDERMIS The epidermis (Fig. 82) is stratified squamous epithelium with a basal layer of columnar cells (stratum germinativum) which produce addi- 4-i S AA M . --.- -- --~.-- FIG. 80. Skin from the lateral body wall is composed of epi- dermis (E) and dermis (D). The hypodermis (H) attaches the skin to the underlying somatic muscles. Sense organs found in the skin include the lateral line (L) and taste buds (T). Goblet cells (G) and alarm substance cells (A) are unicellular glands lo- cated in the epidermis. Melanophores (M) are usually located in the hypodermis or a superficial layer of the dermis but may also be found in the epidermis. Bouin's; H & E; X 140. FIG. 81. The epidermis and dermis are easily distinguished using connective tissue stains. The dermis, composed of col- lagenous connective tissue, has stained green. Alarm substance cells are a prominent part of the epidermis. The lateral-line canal contains a neuromast in which the sensory hair cells have stained darker than adjacent cells. Except for the neuro- mast, the canal is lined by squamous epithelium. This skin was from a 30 mm TL juvenile and is thinner than that of an adult. Bouin's; Masson's; X 320. tional epithelium. Cells become squamous in the outer epithelium but are not keratinized. Goblet (mucous) cells are present in all regions of the body but are especially abundant in the oral cavity. Alarm substance or club cells are also present in all areas except on the barbels (Fig. 126), inner surface of the operculum (Fig. 170 and 24) and lips. The term alarm substance cell (Schrcckstoffellen) was proposed by Pfeiffer (1962) for the club cells of Ostariophysi because of morphological and functional differences be- tween these cells and club cells of other super- orders. The alarm substance cells of channel cat- fish are large (usually 50 to 60 /) with a centrally located nucleus which is usually double. Shape is usually spherical or oblong but is sometimes distorted by folds in areas such as around fins. These cells never extend to the surface. The "fright substance" which they contain is released only when the epidermis is injured (Pfeiffer, 1960, 1962, 1963, and 1977). Melanophores are present in some areas of epidermis. Taste buds and pit organs are also located in the epidermis (Chap. 9). DERMIS The dermis is composed of fibrous connective tissue. A compact layer is located beneath the epidermis; and the hypodermis, composed of loose connective tissue, lies between the compact layer and underlying tissue. Some regions of the hypo- dermis contain adipose tissue. Melanophores are located above and below the compact layer of the dermis except in ventral (white) portions of the skin. The melanophores immediately beneath the epidermis sometimes appear to lie in a thin layer of loose connective tissue superficial to the compact layer. The hypodermis is thin over most of the body but is thick in some regions such as parts of the head and fins. The lateral line is located in the dermis (Chap. 9). Fins The fins are covered by skin and supported by lepidotrichia except for the adipose fin. The pec- toral fins (Fig. 83) and dorsal fin have a hard ray or spine which is quite unlike the unmodified lepidotrichia but which develops from lepido- thrichia (Reed, 1924a). The caudal, pelvic, and anal fins are similar to the pectoral and dorsal fins except no spine is present. The fins, except for the adipose fin, have epi- dermis with a reduced number of alarm substance cells (Fig. 84). The compact layer of the dermis is reduced and the hypodermis is expanded to fill the space between lepidotrichia. The lepido- trichia are composed of bilateral bony elements which have nerves and blood vessels between them. The adipose fin (Fig. 85) is composed of a medial layer of loose fibrous connective tissue cov- ered by skin. The dermis of some portions of the fin has additional connective tissue arranged #5 S - ....- 4 19* . FIG. 82. The epidermis is stratified squamous epithelium. The basal layer is the stratum germinativum (S), and the cells be- come flattened distally. Goblet cells (G) have vacuolated cyto- plasm and a flattened, basally located nucleus. The alarm sub- stance cells (A) are very large and have a double nucleus. Bouin's; H & E; X 600. .- E~ FIG. 83. Tranverse section of pectoral fin showing the spine (S) and lepidotrichia (L) which are formed from bilateral ele- ments. The epidermis (E) has fewer alarm substance cells and goblet cells than the skin of the body. The dermis consists of a very thin compact layer supporting the epidermis and loose areolar tissue surrounding the lepidotrichia. Bouin's; II & E; X 25. 9(9 A *~ .4 A..,, 'WI 5% A I FIG. 84. An enlargement of the skin (S) and lepidotrichia (L) seen in Fig. 83. Bouin's; Masson's; X 175. in distinct bundles. Adipose tissue, which is not an important constituent of this fin, is sometimes present within the central connective tissue layer near the fin base. The epidermis of this fin is similar to that of the body. A I Axillarv Glands Multicellular axillary glands (Fig. 86 and 87) are located beneath the skin dorsal to the pectoral fin. Axillar) glands seem best developed in finger- lings and were not found in large adults. The structure of these glands in other species has been described by\ Reed (19241)). The axillary gland is surrounded by a thin sheath of fibrous connective tissue, and a small pore opens near the base of the pectoral spine. The lumen is filled with vacuoles of a clear staining substance divided )by thin septa. Large cells which are similar to the alarm substance cells of the epidermis are associated with the septa and gland wall. Thicker septa divide the gland into lobes. Epithelial cells and large cells with fine granules line the gland wall and interlobular septa. The function of the axillary gland has b)een associated xwith the production of toxins which could be injected by the spines of the fins (Reed, 1907). This hypothesis seems tenuous for several reasons. No duct or other means of transferring the contents of the gland to the spine tip exists. The spine and surrounding epithelium of some species is toxic, at least to other fish (Birkhead, 1967), without the contents of the axillary gland, an(d the dorsal fin spine which has no axillary gland is as toxic as the pectoral spines. The spine and covering epithelium of channel catfish were not toxic to Gambusia (Birkhead, 1967) but may he toxic to mammals. A .5 F - k FIG. 86. The axillary gland (A) has a pectoral fin (F). Tranverse section of 11 & E; X 70. Ct - :;-P ; - s d * 4 A* ;"d t FI(;. S5. The adipose fin has a medial layer of fibrous con- nective tissue (C) covered hby skin. The dermis has distinct bun- dies of connective tissue (B) in addition to the usual fibrous connective tissue. The epidermis is similar to that of the body. Adipose tissue is sometimes present in the central layer of the fin. Bouin's; II & E: X 120. FIG. 87. The axillary gland is filled with clear staining vacu- oles. Thin, irregular septa (S) divide the vacuoles, and large cells resembling alarm substance cells (A) are associated with the septa. Larger septa (L) divide the gland into lobes. The wall of the gland is lined with epithelial cells (E). Bouin's; II & E; X 240. pore (P) dorsal to the a fingerling. Bouin's; I~F~ CHAPTER EIGHT MUSCULAR SYSTEM Muscles are of three basic types: skeletal, smooth, and cardiac. The skeletal or striated mus- cles (Fig. 88 and 89) are usually located so that they move elements of the skeleton, and these muscles will be described grossly in this chapter. Smooth muscle (Fig. 90 and 91) is found in vis- ceral organs and blood vessels and may form dis- tinct layers or be mixed with other tissues. Its location is described in the discussions of the organs in which it is found. Cardiac muscle is found only in the heart and is described in Chap. 3. FIG. 90. Smooth muscle fibers are not striated and have cen- trally located nuclei. Each cell is much smaller than striated muscle fibers. Urinary bladder; Ielly's; H & E; X 320. ~~5 ii~~ w~ FIG. 88. Skeletal muscle is composed of longitudinally ori- ented parallel fibers which have cross striations. Each fiber has several nuclei located peripherally. Bouin's; H & E; X 800. FIG. 91. This transverse section of smooth muscle demon- strates the small size and centrally located nuclei characteristic of this tissue type. Myofibrils seen in skeletal muscle are not visible. Urinary bladder; Bouin's; H & E; X 600. The musculature of I. nebulosus, described by McMurrich (1884a), is nearly identical with that of I. punctatus. However, some of the terminology used hy MeMurrich is no longer used; therefore, it has been modified to agree with more recent authors such as Greene and Greene (1913) or Edgeworth (1935). The muscles were examined grossly in fresh, formalin-preserved, and boiled specimens. Al- FIG. 89. The peripherally located nuclei and large size of though boiling destroys the connective tissue at- skeletal muscle fibers are seen in this transverse section. Each taching the muscle to bone, this method was fiber is composed of numerous myofibrils which appear as dots at this magnification. Bouin's; H & E; X 320. found to be very useful. Fresh or frozen speci- k, - mens were placed in water which was then heated and boiled briefly. Overcooking resulted in the muscles falling from the skeleton in which case the bones were used in the study of the skeletal system. Superficial connective tissue, which ob- scures details of the musculature on fresh speci- mens, was easily removed from properly cooked specimens, and the muscles were easily dissected. Histological sections of fingerlings were useful in determining the origin and insertion of some smaller muscles. The use of sections for examina- tion of muscles of the branchial arches was par- ticularly beneficial since these muscles were diffi- cult to examine grossly without disturbing their normal relationships. The innervation of some muscles were also confirmed from sections. Adductor mandibulae L evator operculi Levator areus palatini Myomeres of the Trunk and Tail The myomeres are segmentally arranged along the body posterior to the head (Fig. 92). Each myomere is composed of muscle fibers arranged parallel to the longitudinal axis of the body. Myo- commata (myosepta) are sheets of fibrous con- nective tissue (Fig. 93 and 94) which separate adjacent myomeres and attach to vertebrae. Most of the muscle fibers of the myomeres attach to the myocommata and thus indirectly to the verte- brae. These muscles form the largest portion of the muscular system and are the most important muscles in locomotion. The myomeres are separated bilaterally in the tail by median dorsal and ventral septa containing the neural and hemal spines respectively. In the Hypaxial myomere Anal f Location of lateral cutaneous area Caudal fin interradials Caudal fin superficial flexor FIG. 92. Lateral view of the superficial muscles. Hot izontal FIG. 93. Myomeres from different regions of the body vary in shape with the anterior region being particularly modified. The septa dividing the myomeres are composed of fibrous connective tissue, and some are supported by neural or hemal spines. 44 M" M FIG. 94. Transverse section of lateral region of the tail of a fingerling. The white muscle (W) of this region is covered with red muscle (1). M, mnyocommata, S, skin; L, lateral line; 1I, horizontal septum; C, connective tissue septum between red and white muscle; N, lateral-line nerve. Bouin's; H & E; X 60. trunk region, the myomeres are separated by the median dorsal septum and the body cavity. A horizontal septum (Fig. 94) extends from the centra of the vertebrae to the lateral line and divides the myomeres into epaxial and hypaxial components. Each myomere has a superficial "W" shape with the center point oriented anteriorly. The mvocom- mata at the horizontal septum extend anteriorly as they approach the vertebrae while extending posteriorly from the dorsal and ventral portions of the myomere. This results in a rather complex three-dimensional shape (Fig. 93). The superficial fibers of each myomere have a darker color grossly than the deeper muscle from which they are separated by a septum of fibrous connective tissue (Fig. 94). This muscle is often referred to as red muscle (LeDanois, 1958) and was termed musculus lateralis superficialis by Greene (1913) who termed the underlying muscle of the myomeres the musculus lateralis profundus. Red muscle is thickest at the lateral line and be- comes very thin dorsally and ventrally. The lat- eral line nerve is located in the horizontal septum separating the epaxial and hypaxial red muscle. The superficial or red muscle of the myomeres is distinct histologically from the deeper white mus- cles (Fig. 94). The fibers of the red muscle are smaller in diameter and have an increase in vascu- larity. Muscles of the Fins ANAL FIN Three types of bilaterally paired muscles are in- serted on each ray of the fin. The inclinator mus- ele's (Fig. 92 and 95) originate from the fascia covering the ventral surface of the myonere and insert on the lateral surface of the rays. The in- clinators produce the sinuous motion of the fin. The erector muscle and depressor muscle directly oppose each other with the erector inserting on the anterior surface of the ray and the depressor inserting on the posterior surface. The erectors and depressors originate from the pterygiophores supporting the rays. The infracarinales are bilaterally paired muscles located midventrally and oriented parallel to the body axis. The median infracarinales (retractor ischii) reach from the posterior pelvic girdle to the anterior pterygiophore of the anal fin. The posterior infracarinales extend from the posterior ptery- giophore to the hemal spines supporting the caudal fin. The infracarinales act to spread the fin rays and may also flex the body ventrally. DORSAL FIN The muscles are arranged as opposing erectors and depressors as in the anal fin, although the origins and shapes of the muscles of the two an- terior modified rays are altered. The erector and depressor of the defensive spine are especially enlarged while those of the first ray, which serves as a locked device, lock the ray in the erected position by sliding it over the dorsal extremity of the pterygiophore. Inclinator muscles are absent except for the pair which insert on the most an- terior unmodified ray and originate from the pos- terior edge of the horizontal plate supporting the spine. The supracarinales are paired, longitudinal nmus- cle bundles in the middorsum. They extend from FIG. 95. Transverse section of anal fin and adjacent body. An inclinator (I) of the anal fin originates (0) from the fascia be- tween the skin and myomeres and inserts on the base of the lepidotrichia (L). S, skin; P, pterygiophore; M, myomere. Bouin's; II & E; X 80. the adipose fin to the pterygiophores of the pos- terior rays of the dorsal fin. These muscles retract the dorsal fin and flex the body dorsoventrally. CAUDAL FIN Terminology of the caudal musculature is that of Nursall (1963). The superficial flexor (Fig. 92) is formed from the posterior myomere of the tail. The muscle inserts on the fin rays by a broad fascia which covers the underlying muscles. The hypochordal longitudinal muscles (upper division of ventral portion of deep caudal muscle in McMurrich, 1884a) originates from the upper hypurals and.inserts by long tendons on the dorsal principle rays. The deep dorsal flexor (dorsal por- tion of deep caudal muscle in McMurrich) orig- inates from the neural spines of the posterior verte- brae and inserts on the dorsal rays. The deep ventral flexor (lower division of ventral portion of deep caudal muscles in McMurrich) is thin and fan-shaped. It originates on the lower hypurals and inserts on the ventral rays. Interradial muscles (Fig. 92) (intrinsic muscles of McMurrich) obliquely connect the rays. Two layers of fibers are present between the central rays with the superficial fibers almost perpendicu- lar to the deeper fibers. PECTORAL FIN The muscles which move the pectoral fins are the adductors and abductors, each of which has separate superficial and deep portions. These muscles are located in the grooves of the cleithrum and coracoid, and some pass through tunnels in these bones. The actions of these muscles not only adduct and abduct the fin but also lock and unlock the first ray which is modified into a spine. The abductor superficialis originates in the groove on the ventral surface of the cleithrum, passes over the bridge formed from the coracoid to insert on the inferior process of the spine and the basis of the unmodified rays. The abductor profundus has two separate parts. One originates from the ventral surface of the cleithrum beneath the abductor superficialis and passes beneath the coracoid bridge to insert on the semicircular proc- ess of the spine. The other part originates from the dorsal surface of the coracoid, passes through the tunnel formed between the coracoid and cleithrum and inserts on the spine with the first part of this muscle. The adductor superficialis originates from the inner surface of the ascending portion of the cora- coid and inserts on the base of all rays except the spine. The adductor profundus originates from the posterior side of the ventral portion of the coracoid, passes beneath a bridge-like spiculum of bone on the coracoid and inserts on the spine of the fin. The cucullaris (trapezius of McMurrich, 1884a) originates from the lower surface to the pterotic, just posterior to the origin of the adduc- tor hyomandibularis. It inserts on the dorsal process of the cleithrum near its articulation with the posttemporal. Numerous fibers from this mus- cle attach to the membrane forming the posterior wall of branchial cavity. PELVIC FIN As in the pectoral fin, this fin has abductors and adductors with each having two parts. The ab- ductor superficialis and abductor profundus orig- inate from the ventral surface of the basipterygia and insert on the fin rays. The adductor super- ficialis and adductor profundus originate from the dorsal surface of the basipterygia and insert on the dorsal side of the rays. Both superficial mus- cles are more laterally oriented than the deep portions. The arrector dorsalis and arrector ventralis mus- cles originate from the external process of the basipterygium and insert on the lateral fin ray. The arrector ventralis is small and easily over- looked, but the arrector dorsalis is easily located on the lateral edge of the pelvic girdle. These muscles were omitted by McMurrich (1884a) but are described in I. nebulosus by Shelden (1937). The infracarinales insert on both the anterior and posterior margins of the pelvic girdle. The anterior portion of the infracarinales (protractor ischii) and the median portion (retractor ischii) can move the pelvic girdle or flex the body dorso- ventrally. The retractor ischii extends lateral to the anus to insert on the anterior pterygiophores of the anal fin. Muscles of the Head The head musculature is distinct from the myomeres by a loss of obvious segmentation and by innervation, in most instances, by cranial nerves. The hypobranchial muscles are an exception which are innervated by spinal nerves reflecting their derivation from anterior myomeres (Romer, 1955). The innervation by cranial nerves and the associa- tion of the head musculature with the visceral arches suggests that these muscles are closely allied with the smooth muscles of the gut which are also innervated by cranial nerves. 46 The innervation of the cranial muscles was used to divide them into groups. The information ott the innervation of cranial muscles given by Me- Murrich (1884a) was used in most cases. \When Mic\Iurrich's description was questionable, verifi- cation was by serial sections or information given by Edgeworth (1935), Singh and Munshi (1968), and Le Danois (1958). EYE MUSCLES Although these muscles are innervated by cranial nerves, they develop from somites of the head and are considered somatic muscles. Six muscles are inserted on each eye (Fig. 100) and are innervated by cranial nerves III, IV, and VI (Chap. 9). Two olblique muscles originate from the anterior orbit. The superior olbliIque inserts on the dorsal margin of the eye and the inferior oblique inserts on the ventral margin. Four recti muscles originate from the posterior part of the orbit. The superior rectus inserts dorsally, the inferior rectus ventrally, posterior (lateral, ex- ternal) rectus inserts on the posterior margin, and the anterior (medial, internal) rectus inserts near the anterior margin. MANDIBULAR MUSCLES These muscles are innervated by the trigeminal nerxe (Cr.N.V). The adductor mandibullae (Fie. 92) is the largest muscle of the head and fills tlhe large depression onil the side of the skoll posterior to the orlbit. It originates from the hyomandibular and the bones just dorsal to it, and it inserts oil the articular and dentary. Many teleosts have three or four subdivisions of the adductor mandi- bulae (Edgeworth, 1935), but these are not dis- tinct in channel catfish. The retractor tentaculi is a specialized muscle which originates from the pterygoid and inserts by a long tendon on the base of the maxilla which supports the maxillary barbel. This muscle is prob- ably a specialized part of the adductor manldibulae (Eaton, 1948; NicMurrich, 1884a). The muscles involved in moving the maxillary barbels are sim- ple in the channel catfish compared to some other siluroids such as Rita rita in wvhich several muscles are involved (Singh and Nfunshi, 1968). The levator arcus palatini (Fig. 92) originates from the posterior edge of the parethmoid and lateral edges of the frontal and sphenotic, and it inserts on the transverse ridge of the hyomandi- bular. The anterior portion of this muscle lies im- mediately beneath the skin while the posterior portion and the insertion of the entire muscle lies beneath the adductor mandibulae. Thlie dilator opetrtlli oriiiiiates froi tlic froital, spheinotic, andl lomandiblar,l passes over theli hyomandilbular, and inserts on the dorsal process of the opercular. The anterior portion of tile dilator operculi is covered by the levator armis palatini, andl the posterior portion is co\eredl y the addluctor mandIibulae. The interl- andibllularis anterior is located on the ventral side of the head and connects the mediati sides of the dentaries. Ihe intermandibularis an- terior is near the syimphysis of the dentaries ani is rather short. The intermallndibularis posterior (genioh oideus of Mc\Iuirrich. 1884a) (Fig.96 also located on the ventrun of the head, originiates from the outer, ventral surface of the ceratohx al and inserts on the dentary near tlhe insertion of the intermandibularis anterior. Two strips of pseudocartilage like that sipporting the larels cross the venitral surface of this nuisele from aii- terior to posterior with the mental and mandi- bulary barbels originating from the anterior por- tion of the strips. IIYOI) MUCSCLES These muscles are innervated bx the facial nerve (Cr.N. VII). The lev ator operculi (lFig. 92) ori- inates from the posterior ridge of the hIomandi- ullar and edge of the pterotic, and it inserts on the upper border of the opercular. The levator operculi lies ininediately beneath the skin. The adductor operculi originates from the pterotic and inserts on the itnner surface of the opercular aid is someitimes dliffiicult to separate from the levator operculi. The adductor arcus palatinli has separate an- terior and posterior portions which lie beneath the skin covering the roof of the mouth. Both por- , FIG. 96. The intermandihulbularis posterior mnuscle (NI) has strips of seultdocartilage (i') crossing the %.entral surface. The mental and inantlihbular harhbels are attachled to these strips. Sagittal section of fingerling 0, small pit organ. Bouin's; II & E; X (0. ':i 9 ~dp: tions are broad, flat muscles. The anterior por- tion originates from the parasphenoid and orbito- sphenoid and inserts on the inner surface of the posterior portion of the palatine. Eaton (1948) refers to this muscle as the abductor tentaculi be- cause of its indirect action on the maxillary barbel. The posterior portion originates from the posterior parasphenoid and the prootic, and it inserts on the inner surface of the pterygoid and anterior hyomandibular. The interhyvoideus is on the ventral side of the head. It originates from the ceratohyal and hy- pohyal, and it inserts on an aponeurosis at the midline. The insertion of the interhyoideus is im- mediately beneath the skin, but the origin is covered by the intermandibularis posterior. This muscle was called the anterior portion of the hyohyoideus by McMurrich (1884a). The hyohyoideus is the constrictor of the branchiostegal rays and has three portions. The pars dorsalis is between the opercular, interoper- cular, and the enlarged first branchiostegal ray. The pars medialis interconnects the remaining branchiostegal rays. The pars ventralis extends from the last ray to the midline. The hyohyoideus was termed the posterior portion of the hvo- hyoideus by McMurrich (1884a) and is sometimes separated into hyohyoideus superior consisting of the pars dorsalis and pars medialis and hyo- hyoideus inferior consisting of the pars ventralis (Singh and Munshi, 1968). The adductor hyomandibularis originates from the lower surface of the pterotic and inserts on the lower surface of the hvomandibular. McMur- rich (1884a) states that this muscle aids the adductor arcus platini in adducting the hyomandi- bular, but Allis (1908) states that this muscle is a retractor or levator rather than adductor. Singh and Munshi (1968) refer to this muscle as the retractor hyomandibularis. BRANCHIAL MUSCLES These are innervated by the vagus nerve (Cr.N. X) or glossopharyngeal nerve (Cr.N. IX) and are used to move the four gill arches and the pharyngeal teeth. Branchial muscles are often difficult to locate in dissections because of their small size and deep location. Most of the branchial muscles are strap shaped and either interconnect the arches or connect the arches to the neurocranium or pectoral girdle. The muscles inserting on the dorsal part of the arches and on the upper pharyngeals will be described separately from the ventral muscles. One muscle, the attractor arcus branchialis (Fig. 97), connects the epibranchial and ceratobranchial of the fourth arch and can not be classified as either dorsal or ventral. This muscle was omitted by McMurrich (1884a). Dorsal mu.scles. A series of seven levatores arncuum branehialia are found dorsal to the branchial arches. These originate from the pterotic and sphenotic and insert on the three anterior epi- branchials and the upper pharvngeal which bears the dorsal phariiyngeal teeth. These are described in detail by McNcMurrich (1884a). Two transversi dorsales are present connecting branchial arches of opposite sides of the pharynx. These muscles and a similar muscle on the ventral side of the pharynx are some of the few unpaired muscles present in the channel catfish. The trans- versus dorsalis anterior connects the first and sec- ond epibranchials and the pharyngobranchials of the left and right sides, and the transversus dorsalis FIG. 97. Sagittal section of pharynx of a channel catfish 4 days after hatching. The epibranchial (E) and ceratobranchial (C) of the fourth gill arch are formed by cartilage and are con- nected by the attractor arcus branchialis muscle (M). This muscle is also present in adults, but the gill arch cartilage is replaced by bone. N, neurocranium, G, gill. Bouin's; H & E; x 180. FIG. 98. Transverse section of the pharynx of a fingerling. The transversus dorsalis posterior muscle (D) connects the upper pharyngeals (U), and the transversus ventralis posterior muscle (V) connects the lower pharyngeals (L). The upper and lower pharyngeals are the bones which bear the pharyngeal teeth. G, gill arch; P, pericardial cavity. Bouin's; H & E; X 32. posterior (Fig. 98) connects the upper pharyn- geals. Obliqui dorsales (interarculales dorsales ob- liqui) interconnect some of the branchial arches. One muscle connects the first epibranchial to the dorsal process of the third epibranchial. A second muscle connects the second epibranchial to the process of the third epibranchial. A third muscle connects the pharyngobranchial between the third and fourth epibranchials to the fourth epi- branchial. Ventral muscles. The subarcualis rectus com- munis (hypobranchialis of McMurrich, 1884a) lies ventral to the branchial arches just lateral to the midline (Fig. 99). It originates from the hypohyal and passes posteriorly. Insertion is by four slips to the second, third, fourth, and fifth ceratobranchials. The transversus ventralis anterior and trans- versus ventralis posterior (Fig. 98) connect the fourth and fifth ceratobranchials of the right and left sides. The anterior muscle was found to con- nect the third ceratobranchials instead of the fourth in some specimens. The anterior muscle crosses the midline and is unpaired, but the pos- terior muscle inserts on a inidventral aponeurosis and is paired. An obliquus ventralis (interarcualis ventralis obliquus) is present on the surface of each of the anterior three branchial arches (Fig. 99). These muscles lie dorsal to the subarcualis rectus com- munis. Each muscle originates near the midline and inserts on the ceratobranchial. ~4cd" "4~ s~i~ - ; r~; ~~ Pli - ~ - 0 FIG. 99 Sagittal section of the ventral pharynx of a fingerling. The subarcualis rectus communis muscle (S) lies just ventral to the ceratobranclials, (C). Its origin from the hypohyal (H) and three of its four insertions are seen in this figure. The obliqui ventrales muscles (0) are present between the subarcualis rectus communis muscle and the ceratobranchials of the anterior three branclial arches. The transversus ventralis anterior (T) con- nects the tw\o fourth ceratobranchia. R, rectus cervicis; I, in- terhyoideus; P, pharynx. Bouin's; H & E; X 25. " , The cleithropharyngeus superficialis and pro- fundus connect the anterior process of the fifth ceratobranchial (lower pharyngeal) to the cleith- rum of the pectoral girdle. Both muscles proceed laterally and ventrally from their insertion. The cleithropharyngeus superficialis originates further posterior and is larger than the profundus. These muscles were termed pharyngo-clavicularis ex- ternus and internus by McMurrich (1884a) while cleithropharyngeus was the term used by Eastman (1971) for similar muscles in Cyprinus carpio. These muscles are similar to the coracobranchialis muscles of other teleosts (Edgeworth, 1935), but since the homology is uncertain the more accurate terms cleithropharyngeus is preferred. IIYPOBRANCHIAL MUSCLES The only hypobranchial muscle present is the rectus cervicis. It originates from the dorsal sur- face of the cleithrum and extends anteriorly to insert on the urohyal. This muscle was termed the hypopectoralis by McMurrich (1884a), and coraco- hyoid by Branson (1966). The name rectus cer- vicis is preferred by Edgeworth (1935) because this muscle seems homologous to the same muscle in tetrapods. It develops from the ventral portion of the anterior mvomeres and is innervated by spinal nerves. The development of this muscle from myomeres is indicated by its segmentation and the presence of myocommata (Fig. 99). ~ .. P CHAPTER NINE NERVOUS SYSTEM The brain and spinal cord form the central nerv- ous system which has cranial and spinal nerves extending to all portions of the body. The auto- nomic nervous system is composed of elements of both cranial and spinal nerves, and literature on this portion of the nervous system of fishes has been reviewed by Cambell (1970). Sense organs include the eyes, ears, olfactory organs, taste buds, and lateral-line organs. These organs are connected to the central nervous system by cranial nerves. Superior oblique muscle Superior rectus muscle Central Nervous System The external surface of the brain is molded in several lobes seen in Fig. 100, 101, and 102. Some lobes correspond to regions of the brain based on embryonic development while others are por- tions of a region. Brain anatomy is more clearly described using the five regions determined from embryology, but familiarity with the various lobes is useful for orientation and reference. Tracts are bundles of nerve fibers connecting discrete centers, often termed nuclei, in the brain Olfactory sac Olfactory bulb Olfactory tract / Anterior rectus muscle Posterior rectus muscle Inferior rectus muscle ( Optic nerve _ l Olfactory lobe -- Optic lobe Cerebellum r FIG. 100. This dorsal view of the head indicates the location of the brain, eyes, eye muscles, and olfactory organs. The brain ex- tends anteriorly to the olfactory bulbs by way of the olfactory tracts. The first cranial nerve is very short and located between the olfactory sac and bulb. The eye is connected to the brain by the second cranial nerve. 50 Corpus cerebelli. Optic lobe Olfactory lobe Olfactory tract Optic (11) Inferior lobe Pituitary gland Trigeminofacial complex (V and VII) Lateral accessory branch( VII Acousticolateralis lobe ,,-Vagal lobe Spinal cord ...- i.... Vagus (X) sopharyngeal (IX) Medulla oblongata FIG. 101. The lateral view of the brain and several cranial nerves. The anteriorly located olfactory bulbs have been omitted. Olfactory tract Saccus Trigeminofacial complex/ (V and VII) Abducens (VI) Medulla oblongata 1 Oculomotor (111) Trochlear (IV) Inferior lobe -Anterior portion of acoustic (VIII) Posterior portion of acoustic (VIII) -- Glossopharyngeal ( IX) Vagus (X) FIG. 102. The ventral view of the brain except for the olfactory bulbs shows emergence of all cranial nerves except Cr.N.T. 51 and spinal cord. The general paths of tracts have been described in several species of fish and have been summarized by Ariens Kappers (1906), Ariens Kappers et al. (1936), and Lagler et al. (1962). The gustatory tracts have been described in ictalurids including channel catfish (Herrick, 1905). The ineninx primitiva (Fig. 103) covers the brain and spinal cord. This membrane is a single layer of fibrous connective tissue. In most areas the meninx primitiva is thin, but a few areas have additional areolar connective tissue. Blood vessels are frequently found in the meninx primitiva which forms the vascular supporting layer of the telae choroideae. Ependymal cells (Fig. 104) are interstitial cells of the nervous system which line the brain ven- tricles and neural canal of the spinal cord, and form a portion of the telae choroideae. When lin- ing a cavity, ependymal cells are usually ciliated columnar cells with tapered bases which become fibrous and extend into the underlying nervous tissue. TELENCEPHALON The telencephalon forms the paired olfactory lobes and olfactory bulbs (Fig. 100). The olfactory bulbs located adjacent to the olfactory sac are connected to the olfactory lobes by long olfactory tracts (Fig. 100). The tclencephalon seems most important in reception and transmission of olfac- tory impulses but is also involved in reproductive behavior, color vision and learning (Bernstein, 1970). The telencephalon is everted (Bernstein, 1970) so that the olfactory lobes are thickenings of the floor of a sac, the ventriculus communis, which *~ " a FIG. 103. Meninx primitiva (Mi) covers the outer surface of the brain and spinal cord. Optic tectum; Bouin's; H & E; X 320. I i,.. i1. i im-i al cells (E1 with cilia line the ventricles of the brain. Bouin's: ii & E; < 470. has an extremely thin roof and walls (Fig. 105). Each olfactory lobe is solid, and except for the most anterior portion, the two lobes are connected ventrally. Ependymal cells are found on the outer surface of the olfactory lobe, and the periphery has a higher density of neurons than the central region. The optic chiasma is the point at which the optic nerves cross and is located ventral to the olfactory lobes. DIENCEPHALON The dorsal side of this region is covered by the cerebellum and the ventral side forms the inferior lobes ( Fig. 102 and 106). The pineal organ ex- tends from the dorsum of the diencephalon, and the pituitary gland (Chap. 5) and saccus vas- culosus are associated with the ventrum. The diencephalon can be divided into three zones. The dorsal zone is the epithalamus which includes the pineal complex. The thalamus is the middle zone and is sometimes divided into dorsal and ventral portions. The hypothalamus is ventral and has efferent tracts leading to other parts of roof of the diencephlalon cov\ering the third \en- FIG. 105. The olfactory lobes (0) of the telencephalon are partialls surroundedl by the thin wsalled ventriculus communis (\) shich is usualls disrupted when the brain is removedl from the cranium. This transverse section was made of the intact head of a 35 mm TI, specimen. C, optic chiasma; F, endorhinal fissure: E, ependsma. Bouin's II & E: X 50. the brain and the neurohypophysis of the pituitarN The diencephalon serves to connect and integrate various parts of the brain and pituitary. A tela choroidae (Fig. 107) is formed from the "8" ~~ i- :~a~: w~ d I iia .~-4~t ,u~ ~.~" C;" j, ,ci ~ la- I~"Q" Illr o t(6~, a~ J~~ f" *- b FICG. 106. This transverse section of the brain has portions of the diencephalon, mesencephalon, and cerebellum. The saccus vasculosus (S) lies between the inferior lobes (I) of the diencephalon, and the pituitary gland (P) is ventral to them. The corpus cerebelli of the cerebellum, with molecular (I) and granular (C) layers, covers the central portion of the optic tecta (0) and the valvula cerebelli (V). VO, ventricle of optic lobe (mesocoel); T, tegmentum of optic lobe; VI, ventricle of inferior lobe. Bouin's; H & E; X 32. tricle and extends anteriorly to the posterior por- tion of the telencephalon. The tela choroidea is composed of the lamina epithelialis of modified ependymal cells and the choroid plexis formed from the meninx primitiva. The pineal stalk is adjacent to the tela choroidea which is covered by the cerebellum. Cerebrospinal fluid which fills the brain ventricles, neural canal of the spinal cord, and the space immediately surrounding the brain is produced by the tela choroidea (Patt and Patt, 1969). Pineal organ. A long stalk connects the pineal organ to the diencephalon. The flattened pineal organ (Fig. 108) andi tubular stalk (Fig. 109) are hollow with columnar cells surrounding the lumen. The stalk begins beneath the forward edge of the cerebellum and extends anteriorly to the pineal located dorsal to the telencephalon just anterior to the level of the optic chiasma. Most of the stalk is in contact with the thin roof of the ventriculus communis of the telencephalon. The cells surrounding the lumen have been de- scribed in several species and are usually sensory 6 ~ FIG. 107. The tela choroidea consists of the meninx primitiva (M) and the ependymal cells (E). It covers the third ventricle (V) of the diencephalon. The tela choroidea is very similar to the thin roof of the ventriculus communis of the telenecephalon except for a slight increase in vascularity. 0, olfactory lobe; Bouin's; H & E; X 320. V.! I *-;CL~ ~"--q ~ r, r ?e~ - ~5- A cells, supporting cells, and ganglion cells (Fen- wick, 1970a). It has been reported that the pineal of Clarias lazera has only glandular epithelial cells with sensory cells being absent (Rizkalla 1970). Another member of the Siluriformes, Corydoras aneus, has few sensory cell outer segments, and the pineal organ seems specialized for a secretory function (Hafeez, 1971). The precise function of the pineal is not known. Some hypotheses regarding its function are that it is a photosensory structure serving as a dosimeter of incident light, a detector of pressure or chemi- cal composition of the cerebrospinal fluid, or a gland which is either endocrine or related to the composition of the cerebrospinal fluid (Fenwick, 1970a). These hypotheses are not exclusive and it is likely that some or all of these functions are involved. The pineal organ of the goldfish serves as an endocrine organ, producing melatonin which seems to inhibit gonadal formation by inhibiting ,~ ' 4g* Am, f- .. 10b. l he pineal organ P') is holiow and flattened. Col- umnar cells surround the lumen which contains an eosinophilic material. The pineal organ is located directly beneath the dermis (D) and dorsal to the telencephalon (T) in this 30 mm TL specimen. A very thin roof composed of meninx primitiva and ependymal cells covers the ventricle (V) of the telencepha- Ion. E, epidermis. Bouin's; H & E; X 350. FIG. 109. The pineal stalk is hollow with ciliated pseudo- stratified columnar epithelium (E) lining the lumen. A layer of nerve fibers (N) surround the epithelial cells, and several capillaries are usually found beneath the simple squamous epithelium covering the organ. The tela choroidea of the dien- cephalon (T) is closely associated with the base of the stalk. Bouin's; H & E; X 350. the release of hormones from goinadotrophic cells of the pitituitary (Fenwick, 1970b). In the same species, both eyes and the pineal organ are neces- sary for normal phototactic response (Fenwick, 1970c). The function of the pineal organ may vary in different species of fish. Hafeez (1971) found pronounced variation in cell types of the pineal organ. Some species seemed specialized for a sensory function while others were specialized for secretion. A secretory function may be predom- inant in Siluriformes since both Cor,,doras aneus (Hafeez, 1971) and Clarias lazera (Rizkalla, 1970) have pineal organs that are specialized for secre- tion. Saccus vasculosus. This organ lies between the in- ferior lobes (Fig. 102 and 106) -with the anterior end dorsal to the pituitary. It can usually be seen grossly as a vascular area between the inferior lobes. The lumen is continuous with the third ventricle with the opening located in the anterior portion of the saccus vasculosus. The folded wall (Fig. 110) has large blood sinuses located in the folds and two epithelial cell types (Fig. 111). Coronet (crown) cells are large, with basally located nuclei and a knobbed process which extends into the lumen. Ciliary processes with globular expansions at the tips extend from the apical portion of each crown cell. Supporting cells located between crown cells have nuclei located in the middle or apical portion of the cell. Apically located nuclei are often triangular in shape. The function of the saccus vasculosus in fish is uncertain. The sensing of changes in water or ventricular pressure (Dammermann, 1910; Kuro- taki, 1961) and secretion of acid mucopolysac- charides (Khanna and Singh, 1967) have been suggested. MESENCEPHALON This region is composed of the optic tectum which forms the superior border of the third ventricle (mesocoel) and the tegmentum which forms the inferior border (Fig. 106). The optic tecta are the optic lobes (Fig. 100 and 101) which are partially covered dorsally by the cerebellum. The wall of the optic tecta have several layers (Fig. 112) which vary in the type of fibers present and density of cell nuclei. The layers of teleost optic tecta have been described by Ariens Kappers et al. (1936), and Schwassimann and Kruger (1968). The function of the mesencephalon involves the reception and integration of visual stimuli re- ceived from the eyes. The optic nerves of channel catfish are completely decussated so that each optic tectum receives stimuli only from the retina on the opposite side of the body. ~~ ~: "~"% L ~:5 ~r~l~(Clk ~ae~d ~ ";; 4_ o IL a 4.. :~ 41 i ~. FIG. 110. The saccus Nasculosus has a folded wall with large blood sinuses (B). Inferior lobes (I) of the brain are on either side of this transverse section. Bouin's; H & E; X 175. FIG. 111. The wall of the saccus vasculosus has two cell types. The coronet cells have basal nuclei and ciliary struc- tures located on knobbed processes (K) extending into the lumen. Supporting cells have apically located nuclei. Bouin's; H & E; X 800. ;~~ ~I~~ P A% a~i4Dl t!: i , iA 4:,' 7 similar graniular aiindl imolecular laxers. llic ainterior medullary velum continues rostrally from the valvula. The dorsocaudal margin of the corpus cerebelli forms the interauricular granular band (Fig. 113) with a large number of small nuclei interspersed with fibers. A tela choroidea (Fig. 113) consisting of a layer of cuboidal ependymal cells covered by the meninx primintiva extends from the interauricular granular hand to the facial lobe posterior to the corpus cerebelli. The cerebellum seems to function in mainte- nance of muscle tone, postural reflexes, and inte- gration of stimuli from the eyes and acoustico- lateralis organs (Bernstein, 1970). Direct stiniu- lation of the cerebellum through implanted elec- trodes has been used in determination of function in Ictalurus (Clark et al., 1960). Stimulation usu- ally resulted in flexion of the body or tail and M FIG. 112. The optic tectum has several layers which have been divided and named in xarious wass by different authors. Using the terminology of Schwassmann and Kruger (1968), five principle layers are present. Starting at the outer surface, these are the stratum fibrosum marginate (1), stratum plexiform ct fibrosum externum (E) stratum griscum centrate (C), stratum fibrosum profundum (F), and stratum grisum periventriculare (P). Bouin's; H & E; X 253. CEREBELLUM The cerebellum develops from the embryonic metencephalon and is composed of the corpus cerebelli and the valvula. The corpus cerebelli arises caudal to the optic lobes and proceeds ros- trally forming a prominent lobe on the dorsal surface of the brain (Fig. 100 and 101). The valvula cerebelli projects rostrally from the base of the corpus cerebelli into the mesencephalic ventricle (Fig. 106). The corpus cerebelli (Fig. 106, 113, and 114) has a very small ventricle which is lined by ependymal cells surrounded by a granular layer composed of small dark staining nuclei. The outer portion of the corpus cerebelli is composed of the molecular layer consisting of fibers and few nuclei. Purkinje cells (Fig. 114) are located between these layers. The valvula has FIG. 11:3. The corpus cerebelli of the cerebellum has distinct granular (G) and moleiilar (NI) Ilavers. These layers continue into the alkulla cerebeclli (V). 'The interauricular granular hand (I) is locatedl on the posterior edge of the cerchellum. The facial lobe (1F) is posterior to the cerebellum. T, tela choroidea; midsagittal section. Formalin; 11 & E; x 35. S3 P. 'M I I" r . -+ * FIG. 114. Purkinje cells (P) are located between the granular (C) and molecular (I) layers of the cerebellum. Bouin's; H & E; X 320. retraction of maxillary barbels. "Stimulus-re- bound", consisting of movement during the stimu- lation followed by movement in the opposite di- rection after cessation of stimulation, occiriired under some circumstances. MEDULLA OBLONGATA This region is formed from the myvelenchepha- lon. The paired facial and vagal lobes (Fig. 100 and 101) are dorsal enlargements, and the acousti- colateralis lobes are lateral enlargements of the medulla. The facial lobes (Fig. 115) are separated by the fourth ventricle lined by ciliated ependymal cells. The ventricle has a thin dorsal covering and flexes to the side as it proceeds ventrally. The vagal lobes are also separated by the fourth ven- tricle, but the ventricle in this region is straight rather than curved (Fig. 116). The medulla A A FIG. 115. The facial lobes (F) are dorsal enlargements and the acousticolateralis lobes (A) are lateral enlargements of the medulla oblongata (MN). The ventricle (V) between the facial lobes has a distinctive shape. 8, eighth cranial (auditory) nerve. Bouin's; H & E; X 12. oblongata extends caudally from beneath the vagal lobes and blends into the spinal cord. Several cranial nerves emerge from the madulla oblongata. Columns of nerve fibers connect these cranial nerves and the spinal cords to other regions of the brain. The medulla oblongata is especially important in the functioning of the reticulomotor system, taste, and audition (Bernstein, 1970). SPINAL CORI) The spinal cord (Fig. 117) has a small central canal surrounded by ependymal cells. Gray mat- ter of non-myelinated fibers is concentrated around the central canal with a single dorsal horn and paired ventral horns of gray matter extending toward the periphery. White matter of nmyelinated fibers is located between the horns. The spinal cord is protected by neural arches of the vertebrae and extends to the caudal pe- duncle. A filum terminale is formed from the posterior end of the spinal cord. It extends dorso- posteriorly parallel to the uroneural and tapers to a point. Melanophores are located in the areolar connective tissue surrounding the meninx primi- tiva. Spinal nerves branch from the spinal cord. Cranial Nerves Ten cranial nerves (Fig. 100, 101, and 102) were found in channel catfish. These nerves are similar in origin and appearance to cranial nerves found in other fish (Lagler et al., 1962; Romer, 1955; Hyman, 1942). Cranial nerves have been described in other ictalurids by Wright (1884), Workman (1900) and Herrick (1901), and these seemed identical to those of channel catfish. Func- hf - A w ,, f~ 5 9..kPC . k s, N FIG. 116. The vagal lobes (V) are located posterior to the facial lobes and are dorsal enlargements of the medulla oblon- gata (NI). X, tenth cranial (vagus) nerve; IV, fourth ventricle. Bouin's; II & E; X 20. FIG. 117. The spinal cord has a central canal (C) and horns of gray matter (D, dorsal horn V, ventral horn) located be- tween white matter. Areolar connective tissue (A) with num- erous melanophores fills the space between the spinal cord and neural arch (N) of the vertebrae. Bouin's; H & E; X 60. tions attributed to the cranial nerves in this chap- ter are those suggested by the above authors. The terminal cranial nerve (CR.N.0) was not found in dissections or histological sections of the region between the olfactory lobes and the olfac- tory bulb. If present, it is fused into the olfactory tract and is not distinguishable from it. The ter- minal nerve of carp is within the olfactory tract but can be distinguished from it in sections (Ariens Kappers et al., 1936). OLFACTORY (I) This short nerve connects the olfactory sac to the olfactory bulb (Fig. 100, 123) and should not be confused with the longer and more prominent olfactory tracts. The olfactory nerves are too short to be easily located. It is a special sensory nerve and is unusual since the nerve fibers are formed from the sensory epithelium in the olfac- tory sac instead of from separate neurons with cell bodies forming ganglia. OPTIC (II) These nerves connect each retina to the optic tectum on the opposite side of the brain. The optic chiasma (Fig. 105) is formed where the optic nerves cross ventral to the olfactory lobes. They enter the ventral side of the brain at the hypothalamus and continue directly to the optic tecta. The optic nerves are special sensory nerves and are similar to a brain tract which results because of the formation of the retina from the brain tube. The fibers originate in the ganglion cell layer of the retina. OCULOMOTOR (III) The oculomotor nerve leaves the brain between the inferior lobes and medulla oblongata dorsal to the saccus vasculosus. The nerve is both somatic motor and automatic in function. It innervates four of the eye muscles which rotate the eye (Chap. 8). The muscles innervated are the super- ior rectus, inferior rectus, anterior rectus, and in- ferior oblique. The autonomic function involves pupillary dilation in certain teleosts (Young, 1931), although in most teleosts the pupil is im- mobile (Munz, 1971). TROCHLEAR (IV) This nerve is small and is often difficult to locate grossly. In sections it was found to leave the medulla just ventroposteriorly to the optic lobe. This location is dorsal and slightly posterior to the origin of the oculomoter nerve. The trochlear is in close contact with the ganglionic complex of the fifth and seventh cranial nerves after leaving the brain. It then follows the superficial ophthal- mic branch of the fifth nerve until it reaches the superior oblique eye muscle which it innervates. TRIGEMINAL (V) The fifth and seventh cranial nerves are united as they leave the brain. This complex originates from the anterior lateral portion of the medulla and just posterior to the level of the optic lobe. These nerves proceed anteriorly briefly after leav- ing the brain and then branch. These branches have been described in detail in I. melas (Herrick, 1901). The trigeminal nerve is a branchial nerve with both somatic sensory and visceral motor functions, and innervates the anterior portion of the head, especially the upper and lower jaws. Taste buds and lateral-line elements are not innervated by the trigeminal. ABDUCENS (VI) The roots of this nerve are located on the ventral surface of the medulla oblongata posterior to the inferior lobe. This small somatic motor nerve in- nervates one eye muscle, the posterior rectus. FACIAL (VII) The facial is closely associated with the tri- geminal nerve. The branches of this nerve in I. melas have been described by Herrick (1901). Visceral motor, visceral sensory, and lateral-line elements are contained in this nerve which serves muscles of the hyoid arch, lateral-line components of the head, and taste buds including those in the outer skin. Taste buds of the skin posterior to the head are innervated by the lateral accessory branch (Fig. 128) which proceeds dorsally from the trigeminofacial complex to the dorsum of the brain. It continues posteriorly from the cranium and through the epaxial muscles. ACOUSTIC (VIII) This special sensory nerve is fan-shaped as it leaves the lateral surface of the medulla (Fig. 115) immediately posterior to the trigeminofacial complex and proceeds directly to the ear. The anterior portion of the nerve goes to the pars superior of the ear. The posterior portion of the nerve, separated from the anterior portion and directed ventrally, innervates the pars inferior of the ear. 58 GLOSSOPHARYNGEAL (IX) This nerve leaves the lateral surface of the medulla just posterior to the acoustic nerve. The glossopharyngeal has visceral motor, visceral sen- sory, and lateral-line components. It innervates muscles surrounding the first gill slit, taste buds in the pharynx, and lateral-line organs on the posterior head. VAGUS (X) The vagus nerve originates from the lateral sur- face of the vagal lobe (Fig. 116). Visceral and somatic sensory, lateral-line, and visceral motor components are present. Muscles of the posterior gill slits and anterior visceral organs of the body cavity are innervated by the vagus. Lateral-line organs of the posterior head and the body, tast(, buds of the pharynx, and other sense receptors of the posterior head are connected to the brain through the vagus. A visceral branch with motor and sensory function innervates the heart and organs of the anterior body cavity. The vagus nerve is important in the para- sympathetic automatic nervous system. Increase in branchial vascular resistance, reduction in heart rate, contraction of the stomach, and possibly con- trol of swim bladder inflation are attributed to parasympathetic stimulation (Cambell, 1970). Sense Organs EYE The general organization of the channel catfish eye is similar to that of other teleosts (Fig 118). Six oculomotor muscles are inserted on the periph- cry of the cve (Chap. 8). The choroid gland found in inany teleosts is absent. Except for the lateral surface, the eye is covered by a partially cartilaginous sclera and a heavily pigmented choroid ( Fig. 119). The spherical lens (Fig. 118 and 120), which is held in place by a suspensory ligament and retractor lentis muscle, is covered by the cornea (Fig. 120). The iris (Fig. 119) is a continuation of the choroid. The optic nerve connects the retina to the mesencephalon. Retinal structure of the channel catfish has been described by Arott et al. (1974) and Naka and Carraway (1975). Rods and cones are present in about equal numbers, and txwin cones are absent. These photoreceptor cells are located in an outer layer of the retina (Fig. 121 and 122). The outer FIG. 119. The iris (I) is a continuation of the choroid (C) and is heavily pigmented. The cartilaginous sclera (S) covers the choroid. The retina (R) contains the receptor cells which sense light focused by the lens (L). Bouin's; H & E; X 160. FIG. 118. This portion of a transverse section of the head of a 30 mm TL specimen has the olfactory lobe of the brain (0), optic nerve (N), and eye. The eye is slightly compressed dorso- ventrally and the lens (L) is not sectioned well. P, optic papilla; R, retina; I, iris; C, cornea. Bouin's; 11 & E; X 35. FIG. 120. The cornea covers the outer surface of the eye. The outer layer of the cornea is composed of stratified squamous corneal epithelium (E) which is continuous with the epidermis of the surrounding skin. The other layer is the stroma or sub- stantia propria (S) which is composed of collagenous connective tissue. The outer portion of the stroma is continuous with the dermis of the skin and the inner part is continuous with the sclera. The lens has an outer noncellular capsule (C) covering the lens epithelium (E) of cuboidal cells. The bulk of the lens is composed of lens fibers (F). Bouin's; H & E; X 320. '4t ils F IG. 121. The retina is composed of sev eral layers. The l argest laxyer contains the ouiter se gmnentsx of rods and cones (R) as welil ax pigriieiit (P). I Xx aNV - ofx aliiili comiipose the outer nuclear lay er (0). 'Ilic ouiter sx ialit ii i'ci (S) is Nery thin and not reatljix dixtiiiguixslicd. T he innier iilear lax' Ner( is comlpo)sedl prim an lx a v o hor izoint al cull fiberx and widely Spaced cell nuclei. Inneri xx iaptic laser (IS) is I )t ated onl the side of the retina closest to the lensx. (..igioii cells are dlis- persed and do not form a dixtiiict laxyer. Tlie leica jl Iigmnenited choroid (C) is located ouitsidec the retina. Bounji; If & E; X< 240. 44 FIG. 122. Bleaching of the retina (1:1000 Chlorox solution) remox cx the mielanin and tapeturn lucidum so that rods (R) and cones (C) are clearly x isible. This retina was light adapted so that the rods are located deeper in the retina than the cones. Nuclei oif pigment cells (P') are also x isible after bleac hing. 0, Outer nuclear layeCr; S, outer sx naptic lav er; I, inner nuclear l axer; IS, inner sx'natic laxver. Bauin's; H & E; X :350. seginl-its of these CellIs areC mobile wvithi their posi- tion determined by light intensity. The migration of pigment from the pigment epithieliuni aCcom- paicis the movement of the outer segments of the photoreceptor cells resuiltin g int adaption for various light intensities. The pig~ment layser has a tapetal pigment, which forms a tapetuim lucidumi, andl melanin. B~oth ty pes of pigment imist be re- moved for clear e'xamilnation of the rods and1 cones (Fig. 122). The nuiclei of the rodls andl cones arc station arv andI are located in the oulter nuclear layer. The photoreceptor cells syniapse with bipolar and1 horizontal cells in the very thin outer synaptic (plexiform ) layer. Cell bodlies of the bipolIar and lIoritotital cells Lis xx lI as anfacrine (ells andI dis- placed ganglion cells are located in the inner nuclear lay er ( Naka and Carraway, 1975). Most of' this layer is composed of horizontal cell fibers with cell bodies of the vsarious cell types wxidely (dispersed. The inner synaptic (plexiform) layer contains synapses between cells of the inner nuLclear layer and ganglion cells. Numerous myelinated fibers are present. Can glion cells are scattered and (10 not form the (distinct lav er found in most vertebrate retinas. Fibers of the gan glioni cells form bundles which proceedl along the inner surface of the retina to optic papillae ( Fig. 118) . Nine to twelv e optic papillae are present ( Naka and Carrawxay, 1973) an(1d sex eral bundles of nerv e fibers exit through each papillae. These nerv e bundles join to form the optic nerve. OLFACTORY ORGAN Chemnoreception in fish is by olfactory organs, taste buds andl perhaps free nervse endings. In an aqulatic environminen t, the distinction betwseen FIG. 123. The olfactory epithelium (E) is connected to the olfactorv bulb (B) by the first cranial (olfactory) nerv'e (1). Sagittal section of 65S min TI, specimen. Bouin's; 11 & E; XK 60. FIG. 124. The olfactory sac (0) has lamellae of epithelium. The epidermis dorsal to the olfactorv organs has several small pit organs (P). Two lateral-line canals (L) are present beneath the epidermis. The break in the dorsal wall of the oltactory sac is an artifact. Bouin's; II & E :32. "smell" and "taste" is unclear since both are medi- ated by dilute aqueous solutions ( Hara, 1971) Behavioral experiments with I. natalis and I. nlcbu- losus illndicate that inll these species the taste buds are iused to locate food, and olfactorx or rgais are used to detect chemical signals (pheromones) as a tx pe of intraspecific communnication (Bardach et al., 1967; Todd et al., 1967). The olfactory organs ( Fig. 100) are located ill olfactory sacs which have anterior and posterior nares. The receptor cells uare located in sensorx epithelium which forms lamellac (Fig. 12:3 and 124). Nerve .fibers from the receptor cells form the first cranial nerve which (liters the olfactorx bulb (Fig. 123). The epithelium cokverinig the olfactory folds (Fig. 125) has four cell types, receptor cells, sup- porting (sustentacular) cells, basal cells, and nlon- sensory ciliated cells. Epithelium covering the dorsal and lateral sides of the olfactory sac has the saimi lour cill tpes anid also has Illlnerouls goblet cells. The receptor cells have elongated nuclei and an cosinophilic process reaching to the surface of the epithelium. Two types of receptorl- cells are found in Phoxinus differing in the struc- ture of their distal tips (Bannister, 1965). The non-sensory ciliated cells have oval nuclei closer to the surface than nuclei of other cells. Support- ing cells have oval nuclei which are less basophilic than the nuclei of receptor cells. Basal cell nuclei lie beneath those of the other cell types. Caprio and Raderman-Little (1978) examined channel catfish olfactory lamellac with a scanning electron microscope. TASTE BUI)S Tlhese giistatory organs are found over the en- tire externial surface of channel catfish as \\el as inside the mouth, phariinx (Fig. 30), and anterior esophagiuis. The gill arches and harbels (Fig. 126) have especially numerous taste buds. Tlihe taste buds have essentiall- the same structure regard- less of location and are i nnerxated by c-ran ial nerves VII, IX, and X (1Herrick, 1901). Taste buds are located iii the epidermis except for those located inll the esophagus xNhere they are in the mucosa (Chap. 4). In regions where the epidermis is thick, the apical portion of the taste hitd is flush with the surface and the dermis forms a pa)illa which reaches to the base of the organ. In thin epidermis the base rests on the dlermis and the taste bud projects above the sur- face of the epithelial cells. Taste luds have a characteristic flask shape (Fig. 127) with centrally located nuclei near the base. Three cell types are present: receptor cells, supporting cells, and hasal cells. Various types of receptor cells have been described from electronll microscope studies (Desgranges, 1965; Storch and iX ta~ ~ Sa e . s " ~ FICG. 125. The olfactory epithelium is primarily composed of nonsensory ciliated columnar cells with superficially located nuclei (N). Other t pes of cells dliscussed in the text are not seen clearly in this figure. The center of each lamellae has numerous capillaries (C). Bouin's; II & E; X 800. FIG. 12(i. The barbels are composed of a central core of pseudocartilage (P) and nerves (N). Skin with a thin dermis (D) forms the outer surface. Numerous taste buds (B) are lo- cated in the epidermis. The epidermis does not have the alarm substance cells found in the epidermis covering most of the body (E). Bouin's; II & E; X 120. been used to demnonstrate the effectiveness of this system (Poggendorf, 1952: Kleerekoper and Rog- genkamp, 1959). FIG. 127. Taste buds are located in the epidermis and have a characteristic shape. Nuclei are located basally with cell pro- cesses extending to the surface. Cell types are discussed in the text. The epidermis of the barbel is stratified with surface cells cuboidal or slightly flattened. Dermis (D), containing nerve fibers, forms a papilla reaching the base of the taste bud. Bouin's; II & E; X 600. Welsch, 1970). The elongated sensory cells are located in the center of the organ and have long processes which form the apical portion of the taste bud. Supporting cells are located peripher- ally between the sensory cells and the sulrround- ing epithelial cells. Oval basal cells are located at the base of the taste bud. The ultrastnicture of the channel catfish taste bud has been described by Grover-Johnson and Farbman (1976). EAR The ears consist of membranous labyrinths em- bedded in the otic region of the brain case lateral to the medulla. The labN rinths are part of the acousticolateralis system which has several types of sense organs with structurally similar sense cells. Each labyrinth (Fig. 128) has a pars superior consisting of the utriculus and three semi-circular canals and a pars inferior consisting of the sacculus and lagena. The sacculuis and lagena of I. ncbr- losus have been described (Jenkins, 1977). The utrictilus, sacculus, and lagena are collectivelxy re- ferred to as otolith organs. The pars inferior is ventral and posterior to the pars superior. All por- tions of the labvrinth are connected and contain endolymph. The pars superior is innervated by the anterior portion of the eighth cranial nerve and the pars inferior by the posterior portion. The par inferior and the swim bladder are con- nected by the Weberian ossicles (Chap. 12) and the perilymph of the sinus impar (Fig. 129). The sinus impar is a fluid-filled sac contacting the sinus endolymphaticus (Fig. 128) which is continuous with the cavity of the labyrinth. This connection increases the sensitivity to sound and raises the upper frequency threshold. Interrupting this con- nection and destruction of the swim bladder have The functions of the lavrinth include mainte- nance and regulation of muscle tone, receptor for angular acceleration, gravity receptor, and sound receptor (Lowenstein, 1971). The semicircular canals and their ampullae are involved with de- tection of angular acceleration and the otolith organs detect gravity and sound. Sem icircular canals and ampuilae. Three senicir- cular canals are present at right angles to each other. Two are vertical and one is horizontal. These canals are surrounded by ])one and cartilage and are composed of dense collagenous connective tissue lined by simple squamous epithelium. Near the utriculus, each semicircular canal has an en- 55- .9 / 2t a E FIG. 128. Transverse section of a 50 mm TL juvenile through the posterior ear region. The pars inferior of the labyrinth is composed of the lagena (I.) and the sacculus (S). The cavity of the labyrinth is continuous with the sinus endolymphaticus (SE) %which is surrounded by the sinus impar (SI). A, asteriscus (otolith) N, medulla oblongata; C, semicircular canals; N, lateral accessorv branch of Cr.N. VII; C, ganglia of Cr.N. X; E, esophagus; H, head kidney. Bouin's; H & E; X 15. 7 R FIG. 129. The functional connection between tilhe swim blad- der and ear consists of the Weherian apparatus and the peri- l'mph of the sinus impar (SI). This transverse section through the posterior head shows the scaphium (S) of the Weberian chain bordering the sinus impar. The scaphium is connected to the intercalarium (I) by the ligamentum scaphium (LS). The ligamentum tripus (LT) connects the intercalarium to the tripus (T) which is connected to the swim bladder. The other Weberian ossicle, the claustrum, forms a portion of the wall of the sinus impar and is not driectly involved in the connec- tion between the swim bladder and ear. The meninx primitiva (P) is thickened ventrally, and slightly posterior to the level of this section it extends to the vertebrae ventral to it forming separate atria sinus impar. M, NMauthner cells of spinal cord; F, myelinated fibers of spinal cord white matter. Bouin's; II & E; X 120. largement called an ampulla. A crista (Fig. 130), which is the sense organ of the semicircular canal, is located on an elevated stalk of connective tissue within the ampulla. The epithelium of the cristae is composed of sensory hair cells and supporting cells. The sen- sorv cells are tall columnar wvith an oval nucleus in the midportion of the cell. Electron microscopy studies indicate that the sensory hair cells of cristae and other acousticolateralis system sense organs are homologous (Lowenstein, 1971). All have several stereocilia and a single kinocilium ar- ranged in a characteristic pattern. Stereocilia are hair-like processes with a uniformly dispersed longitudinal fibrillae, while kinocilia are true cilia with the typical tubule arrangement of cilia. The sensory hairs are embedded in a cupula composed of a jelly-like substance which in life reaches to the opposite side of the ampulla (Low- enstein, 1971). The cupula shrinks during fixation but is usually not lost during specimen prepara- tion as it is from neuromasts of the lateral line. Deflections of the cupula due to angular accelera- tion bend the sensory hairs resulting in stimulation of the sensory cells. Otolith organs. Three sacs are present in the labyrinth. Each contains an area of sensory epithe- lium, a macula (Fig. 131), which is associated with an otolith. An additional area oC sensory epithelium, the mactila neglecta, is located near the junction of the pars superior and pars inferior. The wall of these organs is composed of dense collagenous connective tissue lined by simple squanmous epithelium. The utriculus is the most anterior sac and is part of the pars superior. This organ seems most important in gravity responses in most species (Lowenstein, 1971). A large horizontal macula covers the ventral surface of much of the utriculus and an otolith lies above the macula. The medially located sacculus and lateral lagena compose the pars inferior (Fig. 128). Each chainm- ber contains a macula and otolith and is continu- ous with the sinus endol phaticus. These organs of the pars inferior function in sound detection and possibly detection of positional changes ( Low- enstein, 1971). The otoliths are calcareous deposits associated mil F1.. 10o. The cristac are located on a stalk of connective tissue xwithin the ampullae. The sensory cells (S) of the cristae are tall columnar with apical sensory hairs embedded in a cupula (C). Supportinig cells (B) have basally located nuclei. Bouin's; II & E; * 250. B"Al F1I. 1:31. The maculae of the various otolith origins are his- tologically similar. The macula of the sacculus is composed of sensory hair cells (II) and supporting cells (S). The sagitta (0) is the otolith of this chamber. Bouin's; H & E; X 240. witlih ach macula. 11'Tese solid deposits ar non-( cclliiular and functionally replace the cupulae of cristae and neuromasts. Each otolith is named ac- cordling to the chamber in \vwhich it is located. The utriculus contains the lapillus, the sacculus con- tains the sagitta, and the lagena contains the asteriscus. The sensory epithelium of the maculae is very similar to that of the cristae except that the macu- lae are much larger in surface area. The sensory epithelium is located on the wall of each chamber replacing the simple sjquamous epithelium lining other areas. LATERAL-LINE SYSTEM Three typos of latera-liiie sense organis arc pres- ent in the skin of channel catfish. Canal neuro- masts are found in lateral-line canals located in the dermis, superficial (free) neuromasts in the epidermis (large pit organs of Herrick, 1901), and small pit organs in the epidlermis. Lateral line. The lateralis (Fig. 80 and 81) ex- tends dlown the side of the body to the base of the caudal fin, and cephalic canals extend over the hcad. Nomenclature of the lateral-line canals is based on the termiiiology of Branson and Moore (1962). The supraorbital canal begins just anteriorly and mnedially to an anterior nare and proceedls pos- teriorly passing dlorsal to the eye. The infraorbital canal begins posteriorly and laterally to the an- terior nare andi proceedls beneath the eye. Just posterior to the eye, the infraorbital canal turns dorsally until it reaches the level of the supra- orbital canal. The infraorbital and supraorbital canals join to form the postocular commissure which proceeds posteriorly. The preoperculomandibular canal starts on the lower jaw just anteriorly and laterally to the man- dibulary barbel and proceeds posteriorly on the lower jaw and then dorsoposteriorly in the pre- opercular bone and over the posterior edge of the hyomandibular bone until it joins the postocular commissure to form the cephalic lateralis which continues posteriorly. The lateralis proper begins immediately posterior to the posttemporal bone. The cephalic lateral lines of channel catfish were partially described by IHerrick (1901) and are similar to those of other silurids. The lateral-line canal opens to the surface by pores which are regularly spaced. Accessory os- sidcles (Fig. 132) surround the lateralis in the re- gion of each neuromast. On the head, these ossicles are often fused in other bones but are separate in the lateral lxdy. Each ossicle is cylin- I (.. 132. IThis longitudinal section of the lateial line of an atult has an accessorN ossicle (0) surrounding the canal. The neuiiromnast has (lark staining, pear-shaped sensory cells (S) and supporting cells with hasalls located nuclei (B). D. ldermis; E, strat lied s uanmous epitheliiumn linin canal N. nerve. Bouin's; II & I- :320. drical \vith an opening for the nerve wxhich con- nects the neuromast to the lateral line nrve. Ac- cessory ossicles beginl developing in the anterior portion of the fish first andl are not found in jruve- iles less than 60 mm TL. The sense organs of the lateral line are neuro- masts (Fig. 132 and 81) and are generally dis- tribuited so that one neiuromast is found bet\veen adljacent lateral-line pores. The sensory cells are pear-shaped and located in the upper portion of the neuromasts. Nuclei of the supporting (sus- tentacular) cells are located basally xxith the cell extending betn c s(nsory cells. Cupuilae were usuallY not present, buit these xwere proably lost (luring fixation or sectioning. Dijkgraaf (1962) indicates that the loss of cupulae from neuromasts during preparation is common and that many re- ports of the absence of cupulae are in error. The ultrastructure of lateral-line sense organism is similar to the sense organs of the ear (Lowen- stein, 1971). The lateral-line canal (Fig. 80, 81, and 132) is located in the dermis, and where accessory ossicles are present, bone siurroiundl s the canal. A layer of loose areolar connective tissue separates these sur- rounding tissues from the very thin stratified squamous epithelium xxhich lines the canal. Neuro- masts are elongated and replace the stratified sqiuamous epithelium lining other parts of the canal. The lateral-line neuromasts are stimulated when water movement bends the cupulac causing a stimulation of the sense hairs. Possible water movements involxved include currents, sonnd waves, and water disturbance caused by moving n objects. Dijkgraaf (1962) concludes that detec- tion of the later type of water movement is the most important function of the lateral-line organs which serve as distant touch receptors. Other authors have concluded that the lateral-line is also important as a near-field acoustic detector (I larris and van Bergeijk, 1962; Tavolga, 1971). Superficial neuromnasts. These differ fromn th, Ineuroinasts of the lateral-line canals primarily 1i) being located singly in the epidermis. The struc- ture and function of these organs in most species seem to be similar to the neuronmasts of the lateral- line canals (Herrick, 1901; 1)ijkgraaf, 1962; Flock, 1971 ). These organs can be seen grossly as a small depression often surrounded by a small unpig- mented area. They occur in distinct rows which sometimes continue the path of lateral-line canals. While superficial neuromasts were often grossly observed, their locations were highly variable. The most frequent locations were on the head but no attempt was made to determine their precise loca- tion due to the variability between specimens. Histology of superficial neuromasts has been de- scribed in I. mnelas (Herrick, 1901) and in I. nebu- losus (Bailey, 1937). These authors refer to these structures as large pit organs and describe them as extending from the dermis to the surface of the epithelium. The organ is composed of sensory and supporting cells which are sometimes sepa- rated from the epidermis by a groove and are wider at the apex than taste buds. Small pit organs (ampullary organs). These or- gans, described in I. melas by Hlerrick (1901), are found on all external surfaces of the body of channel catfish but are most abundant on the head ( Fig. 124. The structure of the sense organs is similar to that of both canal and superficial neuromasts, but they are located in a depression of the epidermis (Fig. 133 and 134). The cupulae and sensory hairs of receptor cells of neuromasts are absent. The ultrastructure of small pit organs has been described by Mullinger (1964). The relationship of these organs to other lateral- line organs is seen in the similarity in structure and by the connection to the central nervous sys- tem. Small pit organs are inner vated by the same cranial nerve branches as other lateral-line organs (Ierrick, 1901). Ilowever, the function of these organs is probably different than other lateral-line organs. l)ijkgraaf ( 1962) concludes that small pit *~Br a FIG. 133. Small pit organs are located at the bottom of de- pressions of the epidenrmis. In regions of thick epidermis, a pore (P) leads to the surtace. T, tangential section of taste hud G, goblet cells; A alarm substance cells; D. dlermnis C, Inmel- anophores; S, stratum germiinati um. Celloidin section: Kol- mer's; II & E; X 175. 44 ": , E FIG. 1:34. A small pit organ has (lark staining sensory cells (S) and supporting cells with basally located nuclei (B). Sen- sory hairs and cupula are absent. 1), dermis; E, epidermis. Bouin's; 11 & E; X 600. organs, as well as ampullary lateral-line organs of other species, are electroreceptors which sense weak potentials or potential changes. we i .-~1;-.I-~ i~~alu~~l i~Ti~"" A)~irB" CHAPTER TEN REPRODUCTIVE SYSTEM The gonads are located in the posterior body cavity immediately ventral to the trunk kidney and swim bladder (Fig. 29) and are attached by mesenteries to the parietal peritoneum covering the kidney and swim bladder. Short ducts extend from the posterior end of the gonads to the genital pore. In addition to the production of gametes, the gonads also produce hormones from endocrine tissue. Spawning behavior has been described by Clemens and Sneed (1957). The sexing of chan- nel catfish based on secondary sex characteristics is discussed in Chapter 2. Morphology of channel catfish spermatozoa was described by Jaspers et al. (1976). Male Reproductive System Thi testes are lolbate, consisting of nminerous finger-like projections. There are anterior and pos- terior regions which can be distinguished grossly (See Fig. 1 of Sneed and Clemens, 1963) or his- tologically. In fresh specimens, the anterior re- gion, composed of paired masses of loblules, ap- pears white compared to the single fused mass of pink lobules of the posterior region. The anterior region, comprising at least three-fourths of the entire testes, has longer, thicker lobules than the posterior region. These distinctions are more pro- notuneed in sexually mature specimens than in juveniles. ANTERIOR REGION OF THE TESTES The anterior portion of the testes is composed of coiled, branched seminiferous tubules with sper- matogenesis occurring along the length of all tubules (Fig. 135). Each lobule is surrounded by a thin tunica albuginea composed of fibrous con- nective tissue which is continuous with the septa which separate the seminiferous tubules. Forma- tion of spermatozoa from the germinal epitheliumn appears similar to that in other vertebrates (Patt and Patt, 1969). Spermatocytes and spermatotids are clamped in small cysts of equal maturity (Fig. 135 and 136). Sertoli cells (follicle or companion cells) with flattened, irregularly shaped nuclei and slightly eosinophilic cytoplasm can often be seen enveloping the cysts of spermatogenic cells. Apparently mature spermatozoa and abundant ' .. ,, * c- ~1 . \. ".~- ~-N FIG. 135. The anterior portion of the testes is composed of seminiferous tubules with spermatozoa (S) filling the lumen of each tubule. The tunica albuginea (T) surrounds each lobule. Numerous mitotic figures are found in the epithelium of the tubules of this testis which was collected in November. Bouin's; I & E: X 1:30. F * 4 FIG. 136. The seminiferous tubule is lined with epithelium (E) composed of spermatogenic cells and Sertoli cells. Sperm- atogenic cells of equal maturity are often grouped together. Fil)rous connective tissue (F) surrounds the tubule, Sperma- tozoa (S) are found in the lumen during all seasons. Testis collected in November. Bouin's; II & E; X 600. mitotic figures are present in the seminiferous tubules of adults during all seasons. As spawning nears, the size of the seminiferous tubules and the quantity of spermatozoa increases greatly (Fig. 137) resulting in an increase in the overall size of the organ. An increase in mitosis is noticeable during winter and spring before spawning. A de- crease in the thickness of the wall can be seen immediately after spawning, and a considerable --~t :-""K~- .r '-r: .;~I~"-i i rj~~ ? ~-1-- :: VC : ~ - .*- N% i A FIG. 137. The seminiferous tubules of this testis collected during April, approximately I month before spawning, are swollen Nwith sperimatozoa (S) (colmpare to Fig. 135). Bouin's; 11 & E: > 60. number of spermatozoa remain in the tubules. Sertoli cells become more prominent after spawu - ing, perhaps because of increased phagocytosis of unused sperm. POSTERIOR REGION OF THE TESTES The posterior region of the testes is composed of branched, coiled tubes, but the cells of the tubule wall are very different from those of the anterior region (Fig. 1.38 and 139). Spernmatozoa are usu- ally not present in the posterior region, although they were found in some specimens after spawn- ing. Seasonal changes are minimal, although Sneed and Clemens (1963) report that the epithelial cells increase in size as spawning season approaches. The function of the posterior region is unknowin. A similar region is associated with the testes of Gillichthys and has been referred to as a seminal .i- --- -9 s~ -i ," a~FI~ sl / , FIG. 138. The posterior lobe of the testis is composed of coiled tubules lined with simple columnar epithelium with very light staining cytoplasm. Spermatogenic cells and Sertoli cells are absent. The tubules are more highly branched than in the anterior region. Bouin's: I & E; X 60. FIG. 139. The simple colunmnar epithelium lining the tubules of the posterior region of the testes has apically located nuclei and very light staining cytoplasn. The tunica albuginea (T) and septa between tubules are composed of fibrous connective tissue. Bouin's; HI & E: :' 240. vesicle (\Veisel, 1949). Sneed and Clemens (1963) found that fertilization and hatching were success- ful without the addition of any substance from the posterior region. ENDOCRINE FUNCTION OF THE TESTES The testes of teleosts are thought to be the source of androgens important in regulation of reproduc- tion, secondary sex characteristics, and reproduc- tive behavior (Hoar, 1969; Liley, 1969). Testicular hormones are thought to originate in interstitial cells (Leydig cells) found ietween seminiferous tubules (G(ottfried and van Mullem, 1967) or in boundarv cells located in the wall of the tubules (Marshall and Lofts, 1956). Neither of these cell types were found in the channel catfish; however, more extensive histochemical tests might demon- strate the presence of these cells. Alternative sources of androgen within the testes are the Ser- toli cells (Hoar, 1969) and possibly the posterior region of the testes which at present has no known function. Female Reproductive System The paired ovaries are tubular in shape and en- closed in a tunica albuginea of fibrous connective tissue covered by mesothelium. Large amounts of smooth muscle are found in the wall of mature ovaries (Fig. 140). The tunica albuginea of juve- niles is poorly developed (Fig. 141). Ovigerous lamellae composed of two layers of oocytes sup- ported by fibrous connective tissue and covered by simple squamous epithelium project toward the center from the tunica albuginea. This lamel- lar structure is seen in longitudinal sections of *~~o," r q z I t P, d I I. a ~_ r 4I T / FIG. 140. The outer ~sall of the ov ary is the tunica albuginea (T) and cont amn snoinmuscle iii adults. Meol elui o rs the outer surf acc. 0. oocs te. Boomns; 11 & F; Y 120. juvenile oxvaries ( Fig. 142). A space remnains in the center of the oxarv xwich is continuious wxith the short ox idluct leadingt to the genital pore. OOGENESIS GDogenesis involves the proliferation of oog-onia by mitosis and the (lexelopmecnt of oocx tes wxhich develop fromt the oogonia. Oogonia ( Fig. 143 ) are found in groups or ])lests" in) the ox igerolls lamlellae andl are most altundlant (luring the summeinr and fall. Oogonia appear simnilar- to uindiffterceitiate(l germ cells of emnbrx os (I lamim, 1927). Oogonia become oocvtes xxci hn meinsis begins. Specialized cells suirrounid the lex elopimig oocx te forming a follicle. Considecrable chan ges it) struce- ture as xxell as an increase in size occiur inl thle follicles as spawvnin g approaches. These changes FIG. 141. This transv erse section of a jux enile ovary shows the mesentery (,\I) attaching it to the peritoneum covering the swim bladder (S). The oXvary is filled wsith primary follicles (F) containing oocvtes which hav e a large, light staining nucleus and strongly basophilic cytoplasm. The tunica albuginea sur- roundling the ov ary is very thin. The visceral peritoneumn covers the external surface and is continuous with the inesenterX'. Bouin's; 11 & E, X 70. I. 142 Th igi inns lamnellac are seen in this longitudinal section of a juv enile us an. Numenrious primary follicles (F) supjported by fibrous connective tissue compiIose the laniellac. A lumen (L) remains in the center of the ov ary and is lined by sim ple squamious epithliium. I he tuniica albuginca (T) sur- round~s the os arN. Hells s; 11 & E; X 120. have b~een described in many species and are often (described in terms of artitrary stages (James, 1946; Cooper, 1952; Brackevelt and NieNlillan, 1967; Combs, 1969; Moser, 1967; Shelton, 1964; See Hobar, 1955, 1957, 1965 for fuirther references). Trhe termninologyN of the structures of the follicle has xvaried among authors. Most confusion has inxvolx ed the nioncellular, striated layer termed zioma radiata inl this chapter. This descriptive term has been used by mnmerous auithors studving 1both hlistology and uiltrastrutcture of species in xvhich this laser- is striated. H urley and Fischer ( 1966), uisin g electron mnicroscopy, found the striations of the zona radliata (of brook trotit to be pores pene- trated by Inicrox illi formed bxy the underlying plasma nmembrmane which they termed vitelline memb~rane. The term zona 1 )ellucida has been usedi for this lay er ( Hoar, 1969 ) but seems less dlescriptixve than zona radiata and can be confuis- ing since somec species hax'e 1)oth a zona radiata and1 a zona pellucidla ( Hurley and Fisher, 1966). This laver has also b~een termed the chorion ( Mlat- texxs, 1938) wxhich seems undesirable because of the use of this term for an embryonic membrane of aminiotes. The term x itelline membrane has also lbeen used for the zona radiata ( Moser, 1967; Braekevelt and McMillan, 1967; Jollie and jollie, 1967), although the use of this term by other authors for the plasma membrane or a b~asophilic layer beneath the zona radiata is confusing. The transformation from oogonia -to oocyte in- xolv es anl increase in the size of the cell and nucleus. The chromatin of the nucleus forms a reticulum, and the nucleolus moxves to one side of the nucleus after wyhich multiple nucleoli are seen. Soon after the oocyte begins to differentiate, a layer of squamous cells can be seen surrounding it. The cytoplasm of these oocytes becomes strongly basophilic and the nucleus stains lightly. Growth and differentiation of the primary follicles often stops at this stage when the diameter is 50 to 80 p. Only primary follicles are found in ovaries of juveniles (Fig. 141 and 142), and they are found in adult ovaries during all seasons. Maturation of the oocyte in preparation for spawning involves the nucleus, cytoplasm, and sur- rounding tissues (Fig. 143, 144, and 145). The nucleus enlarges and the nuclear membrane be- comes irregular. The cytoplasm becomes vacuo- lated, especially near the plasma membrane, and yolk is deposited. The cytoplasm becomes less basophilic than in primary oocytes and becomes eosinophilic as yolk is deposited. An eosinophilic zona radiata develops around the oocyte and a basophilic layer, possibly the plasma membrane, can be seen beneath it in more mature oocvtes. Distinct striations are present in the zona radiata during the late development. A layer of follicular cells (granulosa) develops from the squamous cells surrounding the primary oocytes. These cells become cuboidal and later columnar. A thin theca of vascular connective tissue forms the outer laver of the follicle. The epithelium lining the ovary covers part of the follicle. The oocytes reach a t G diameter of 3 to 4 1n11 before spawning. The fol- licular cells become granular and separate from the zona radiata as spawning approaches. N FIG. 144. This oocyte is slightly more mature than the pri- mary oocvtes seen in figures 141 and 142. The cytoplasm (C) and nucleus (N) are enlarging, and vacuoles (V) are seen in the periphery of the cytoplasm. The follicular cells (F) sur- round the oovte. Bouin's; IH & E; X 800. 4 FIG. 143. Oogonia are found in groups (G) associated with the epithelial lining (germinal epithelium) of the-ovary. The group of oognia results from repeated mitotic division. The oogonia have 4 to 5 a diameter nuclei with a centrally located nucleolus and eosinophilic cytoplasm. Cell margins are indistinct and no follicular cells are present. A maturing oocyte has clear vacuoles (V) in the cytoplasm, an irregular nuclear membrance and several nucleoli. This oocyte is surrounded by a dark staining zona radiata which is not yet striated, a layer of cu- bodial follicular cells, and a thin theca. Bouin's; Masson's; X 240. FIG. 145. The zona radiata (Z), a single layer of columnar follicular cells (F), and theca (T) surround the oocyte. Vacuoles (V) of yolk are located in the periphery of the cytoplasm. A thin basophilic layer occurs between the zona radiata and cytoplasm. Faint, radial striations are present in the zona radiata. Bouin's; II & E; X 1200. SPELNT OVAIES Atretic follicles wecre not found b)efore spawning lbut wxere c ommnon in some specimens for a few weeks after spawning (Fig. 146 and 147). The follicular cells enlarge and phagocvtize the oocytes, which wvere not spawxned. The resulting structi it (luring phagocy tosis resemlIes the corpora atreti(t or preox ulatory corpora lutea reported in oil or teleosts ( Lambiert and \-on Oiordt, 1965; Brct- schneider and1 Duvvene dc Wit, 1947) The follicutlar cells of empty follicles in spent ovaries often enlarge, and the connectiv e tissue surrounding the follicle thickens and becomnes more vascular (Fig. 146 and 148). Although the follicuilar cells become x acuiolaled, the changes are not as 1 ronouinced as in post ovulatory corpora lutea reported in other teleosts (Samutel, 1943) and elasmobranchs ( Hisaxv and Albert, 1947). The use of the term corpora lutea is queistionable but has been defended by I bar ( 19.57, 1965, 1969). ENDOCRINE FUNCTION OF THE OVARY Estrogens aud progesterone hav e been found ini the oxvaries of many teleosts and may be produced by the ovarian b licles and corpora littea as they -. '-~w ~. -1 4v ' ' t 7 '44 Fl G. 1 47. Atrctkc Inlieics \%ci c only found in spent ov aries. 1Ii follici uar cells (F) become tall columinar cells with apical nuclei and( Lix C x actinlated vs tn'lasm. Remain s of tile oocyte 0) are present in thle follicle. liouin's; 11 & E, X 240. are in higher ecrtebrates ( hoar, 1969 ). These hormones are important in the control of repro- ductix e cycles, secondary sexual characteristics, and behav ior (11oar, 1969; Lilev, 1969). The follicular cells of follicles and corpora lutea-like structures are present in channel catfish and seem to be likely sources of hormones from the ovaries. a;, ~HQ~ - w ~, ~ ~ ~ ~:A 1-IG. 146. An os ars 2 das after spawning contains .itretic follicles (A), empty follicle, (E), and young follicles. Primary follicles (F-) appear idIentical to those in juvecniles. Bouin's; 11 & F X 25. FIG. 148. The eitN folliclcs of spent ov aries arc collapsed with a space (S) remaining in the location once occupied by the oocyte. The s'actiolatcd follicular cells (F,) are tall columnar wuith basal nuclei, and the theca (T) is thickened and highly vascularize(I. Bouin's; HI & E; X 240. CHAPTER ELEVEN RESPIRATORY SYSTEM The gills are used for gas exchange between the blood and water. Accessory respiratory organs and pseudobranchs are absent in the channel catfish. The gills are important in osmoregulation because water can easily enter the blood at the gills and because of chloride cells located on the gills which may transport monovalent ions into the blood (Philpott and Copeland, 1963). The gills are also important in the excretion of nitrogenous wastes in the form of ammonia (Smith, 1929; For- ster and Goldstein, 1969). Pharynx Four pairs of gills are present in the pharynx (Fig. 29). The gills are covered by the operculum so that only one external opening is present on each side. The opercular covering forms a cavity in which the respiratory surfaces of the gills are located. Water flows through the gill slits, which are guarded by rakers, and then over the gills. Unidirectional water flow is maintained by the oral valve (Fig. 149) and branchiostegal mem- brane. The oral valve consists of flaps of skin just posterior to the upper and lower jaws which pre- vents water from exiting through the mouth. The opercular membrane is supported by branchio- stegal rays (Chapter 12) and prevents water from entering through the opercular opening. Gills Each gill consists of a gill arch, gill filaments, and gill lamellae (Fig. 150). The gill arch is sup- ported by the branchial arches of the branchio- cranium (Chapter 12). In juveniles, varving amounts of cartilage are present supporting the arch because these bones are preformed in carti- lage. Two rows of gill rakers and filaments are present on each arch, and the lamellae (secondary lamellae) branch from the filaments. The lamellae are the actual respiratory surfaces. Electron micro- scopy has been useful in understanding the struc- ture of lamellac ( Hughes and Grimstone, 1965; Newxstead, 1967). The gill filaments (Fig. 151, 152, and 153) are supported by cartilage which is unlike the hyaline cartilage of other parts of the body (Chap. 12; Fig. 169). The filaments are flattened in cross sec- tion with the cartilage located near one side. The afferent arteriole is located near the cartilage and the efferent arteriole is located on the opposite side of the filament. Stratified squamous epithe- lium covers the filament. Goblet cells are most abundant on the margins near the arterioles, and alarm substance cells are absent. The gill lamellae project from the sides of the filaments. The gill lamellae (Fig. 154 and 155) are com- R 4 F ~V 4 V FIG. 149. The oral valve consists of folds of skin (V) immedi- ately posterior to the oral teeth (T). Sagittal section of finger- ling. Bouin's; H & E; X 60. FIG. 150. Each gill arch has two rows of filaments (F) which project into the opercular cavity. Two rows of gill rakers (R) project from the inner surface of each arch. Lamellae, the actual site of gas exchange with the water, project from both sides of each filament. Formalin; H & E; X 25. FIG. 151. Lamellae (L) project from both sides of the gill filament sectioned longitudinally. Gill-filament cartilage (C) supporting the filament is seen in this section. Formlin; H & E; X 240. FIG. 152. This longitudinal section of gill filament is near the center of the filament where cartilage is absent and lamellae are their maximum length. The epithelial cells appear different than those in Fig. 151 because of the difference in fixation. Bouin's; H & E; X 240. GIC. 154. Chloride cells (C) are more cosinophilic than other cells of the gill epithelium and are abundant between lamellae. The lamellae have pillar cells (P) which separate the walls of squamous epithelium. Bouin's; H & E; X 600. E If 44 4. 4 w4&Z F I a -9 is- 4, C *4~A .~' #4 44 444 FIG. 153. Transverse section of a gill filament. The support- ing cartilage is located on the side of the filament just internal to the afferent arteriole (A). Blood flows from the lamellae through the efferent arteriole (E). Goblet cells (G) are most abundant toward the margins of the filaments. Bouin's; H & E; XK 240. FIG. 155. An electron micrograph of a gill lamella. Pillar cells (P) support the lamellac and flanges of these cells (F) surround the blood sinusoids (S). A basement membrane under- lies the epithelium (E) which is usually two cells thick. R, erythrocyte. Glutaraldehyde; uranyl acetate and lead citrate; X 8,000. posed of a thin epithelium covering pillar cells. The pillar cells support the lamellae and have flanges which surround the blood sinusoids. The lamellae are open except for the pillar cells which connect the sides. Blood enters the lamellae fromn the afferent arterioles of the filaments and exits into the efferent atreriole. Chloride cells (acido- philic cells) (Fig. 156) are located near the base of the lamellae and in the trough between lamellae. The effectiveness of the gill lamellae for gas exchange is increased because of counter current exchange (Lagler et al., 1962). The blood flows through the lamellae in the direction opposite of that in which water flows over the lamellae, and exchange may be efficient enough so that only passive diffusion is necessary to supply oxygen to the blood (HIughes, 1966). j.4, i :9 i " ;<">"'* FIG. 156. Electron micrograph of a chloride cell near the base of a lamella. Mitochondria (Mi) and endoplasmic reticulum are the most abundant elements of the cytoplasm. The nucleus of the chloride cell is not present in this section. E, epithelial cell. Glutaraldehyde; uranyl acetate and lead citrate; X 14,600. 0~a-3 ":~ b : : e _ R^ "i3'2 k ,: II (~ Y ; ; .IZ u 4 i 4, CHAPTER TWELVE SKELETAL SYSTEM The skeletal system (Fig. 157) consists primarily of bone and hyaline cartilage. Larval specimens have a predominantly cartilaginous skeleton with bone becoming more prominent with increasing age until the skeleton is almost entirely bone in the adult. Several of the bones become tightly fused so that distinction between them is difficult or impossible. The bony elements of the skeletal system were examined grossly in cleared and stained (using the techniques of Taylor, 1967) specimens rang- ing from 40 to 100 mm TL and in larger specimens from 20 to 60 cm TL which were cleaned of flesh by boiling. Some parts of the skeleton of smaller fish were also cleaned by boiling. Histological sections were sometimes useful to clerify the rela- tionship between certain structures. The osteology of I. nebulosus has been described by McMurrich (1884b). This reference is useful in the study of the skeleton of I. punctatus, but more recent studies and changes in terminology have outdated this reference. Most of the termi- nology in this chapter follows that found in recent references such as Lagler et al. (1962). The terminology of the skull and caudal fin is dis- cussed with those portions of the skeleton. Skull The reduction or absence of several bones indi- cates the specialization of the skull. Bones which are absent include the parietals, opisthotic, subo- percular, and symplectic. The maxillae, which support the maxillary barbels, are greatly reduced. Several bones are fused or tightly joined together so that nearly intact specimens are easily prepared. A drawing of the lateral view of the skull of I. punctatus has been published by Gregory (1933) and the similar skull of I. nebulosus has been described by McMurrich (1884b) and Kin- dred (1919). The description by Kindred is de- tailed and includes developmental information, but does not include the branchial region. The separation of the skull into various regions and other terminology is based on Gregory (1933). NEUROCRANIUM The bones of the neurocranium surround the brain and the sense organs of the head including Caudal Vertebrae Uroneural al Spines Epural Ii -1 Hypurals FIG. 157. Lateral view of the channel catfish skeleton. 74 much of the cephalic lateral-line canals. The an- terior portion of the neurocranium is the olfactory region which is associated with the olfactory organ. The orbital region surrounds the eye, but several of these bones also encase the lateral-line canal. The otic region forms the posterior part of the brain case, the otic capsule, and articulates with the pectoral girdle. The basicranial region forms the base of the neurocranium and points of articu- lation for the vertebral column and pectoral girdle. Olfactory region. This region forms around the ethmoid cartilage of the larval fish. The meseth- moid (supraethmoid) (Fig. 159) is the most an- terior bone of the skull and is unpaired. The shape of the mesethmoid can be used to identify the species of Ictalurus and Pylodictis (Paloumpis, 1964; Calovich and Branson, 1964). The pareth- moids (ectethmoid) (Fig. 159) are lateral to the mesethmoid and form the anterior margin of the orbit. According to Gregory (1933) this bone in- cludes the prefrontal. The vomer (Fig. 160) is unpaired and lies on the ventral side of the neurocranium forming part of the roof of the mouth. The nasals (Fig. 159) are long thin bones which are loosely attached to the skull. These enclose part of the supraorbital lateral-line canal. Orbital region. The frontals (Fig. 159) form the dorsal portion of the orbit and the largest part of the roof of the cranium. Two longitudinal fontanelles lie between the frontals. The or- bitosphenoid and alisphenoid (Fig. 158) lie medial to the orbit. The remaining bones of the orbitual region constitute the suborbital (infraorbital) series (Fig. 158) and enclose the infraorbital lateral-line canal. The most anterior member of this series is the lacrymal which lies dorsal to the olfactory organ. The second suborbital (jugal) lies anterior to the parethmoid. The remaining four suborbitals lie ventral and posterior to the eye with the most dorsal of these being very small and occasionally absent. The entire suborbital series is loosely at- tached to the skull. The suborbital series of I. nebulosus as described by Kindred (1919) is slightly different than above and is composed of a total of seven bones including the lacrymal in- stead of six as in I. punctatus. Otic region. The sphenotic and pterotic (Fig. 159) form part of the dorsum of the skull and part of the side of the neurocranium. The pterotic is one of two points of attachment of the post- temporal of the pectoral girdle. The remainder of the dorsum of the skull is composed of the un- paired supraoccipital (Fig. 159) which extends posteriorly to attach to the dorsal fin. The prootic (Fig. 160) forms a large portion of the side of the neurocranium. The epiotic and exoccipital (Fig. 160) lie on the lateroposterior corner of the neuro- cranium and the exoccipital forms the lateral mar- gins of the foramen magnum. The posttemporal (Fig. 158, 159, and 160) and supratemporal (scale bone) (Fig. 158 and 159) are involved in support of the pectoral girdle and are firmly attached to the skull. The posttemporal is attached to the skull dorsally at the pterotic and epiotic and ventrally at the basioccipital. The supratemporal covers the dorsal portion of the posttemporal and is tightly joined to the posterior margin of the pterotic and lateral margin of the supraoccipital. The sutures between the supra- temporal and surrounding bones are easily seen on well cleaned specimens, and these bones can be separated after prolonged boiling. The supra- temporal is not shown on the drawing of I. punc- tatus in Gregory (1933) and is not mentioned by McMurrich (1884b) or Kindred (1919). The subtemporal (Fig. 158 and 159) is a small, loosely attached bone lying between the dorsal end of the preopercular and the pterotic. The subtemporal surrounds part of the preoperculo- mandibular lateral-line canal. This bone is not mentioned by Gregory (1933) but is described by Kindred (1919). Basicranial region. The parasphenoid (Fig. 160) is a very long bone extending from the meseth- moid to the basioccipital. A portion of its ventral surface is covered anteriorly by the vomer. The basioccipital (Fig. 160) forms the ventral por- tion of the foramen magnum, and a posterioventral disc serves as the attachment for the vertebral column. BRANCHIOCRANIUM (VISCERAL SKELETON) This portion of the skeleton includes the bran- chial arches which support the gills and the mandibular and hyoid arches which have evolved from the anterior two visceral arches (Goodrich, 1930). The oromandibular region includes the bones which are formed from the palatoquadrate cartilage, bones of the secondary upper jaw, and bones of the mandible. The hyoid region in- cludes bones developing from the cartilage of the hyoid arch plus several other bones located in this region of the skull. The branchial region includes bones forming the gill arches and supporting the pharyngeal teeth. 75 ~~1 - 'Modified 'Spt e r yg90p ores L acry ma Maxilla Ptrgopoe Palatine Rb FIG. 158. Lateral view of the skull, anterior vertebrae, pectoral girdle, and dorsal fin. '\I ;X I1,1 Nasal Lacrymal 1 st suborbital K~ ~ r ~ ~ 2d Suborbital Articula~r 4th r V !I Ai5th I. - Frontal Quad rate Id/i A erygoicl 4- Hyomandibular -Pr eoper Cuar Oper Lular -Sphenotic S upra temporal Posttemporal Sripr aoccipital Comrplex vertebra Pectoral spine 5 th Vertebra Modified pterygiophores Locking ray Dorsal spine FIG. 159. Dorsal view of the skull, anterior vertebrae, pectoral girdle, and dorsal fin. 77 PremaxdIaM sethmad Palatine - Parasphenoid Par et h mid Sphenot ic 8 a siQclri nt a Posttem pora I Supraoccipital . - Yeter f. Ciarrintou FIG. 160. V.eotral view of the ocurocranium w ith several additional hooes included. Oromandibular region. The p~alatines F'ig. 160) are rod shaped l)otts wxhich form part of the palate and1 aid inl suipport of the maxi llae. The funlctiotl of the pilati ict inl the ab~ductionl of' the maxil lary bad )e has beeti (lcscribe b( Fl) aton K 1948). The pterv goid (mietaptery goid ) and (quadrate ( Fig. 1.58, 159, and 160) are plate shaped and firix fused to the I l o.nandil I lar] an d pt-c- opercular to form at large lateral plate. Ilte j tiad- rate articulates wxith the lower jaw. The ectoptel x - gToici present ilt I. 1tC1)tlo.siv ( Kindred, 1919) is al)seflt inl L. /)lintati.S. The premaxillae ( Fig. 160) lbear all of the teeth of the upper Jaxxt\\ andl are attached to the v entral surface of the anterior por tion of the niesethnmid. The maxillae Figr. 1538 and 1.59) are redutced1 and atre mnerely rods supportinig the b~ase of the maxillary barbels. The lowerci jaw consists of two blles wxhich forml around \ tckel's cartilage. The anterior bone is th decclntary ( F~ig. 1.58 ) ) and lbears all the teeth of the lower jaw and surrounds at port ion of the preoercilotnndibtlarlateral-line canal. Ti gri tly fused to the dentary is the atrticutlar (Fig. 1.58) which articulates with thec ojuadrat'. IIHioid )cgiont The lmix onciibutlar (i.1.58 at 1( 160o) is a larg('C flat bOt t( prex iousIlx tuettiot ted ats fortin ilg part of' a 1large' lateral plate,. It is attaiched~( to the lateral edge of the neurocranitim, anld at seisof hol ies dex eloping from the remfaindclr )f' the hx oidl arch is attached( to the loxxer surf ace of the plate formted fron the lix omiadibular and adjacent bones. The re mainling bonecs of the hx oid arch are the ittethx al, epihx al, cer-atohx al, dorsal lix pohvyal. and xventral hx pohx al (Fig. 162). These lotri atl arch to w hich the anltetmot bianlchial arch is attached. Eight branchiostegal rays ( Fig. 161 ) are at- tached to the epihx al and ceratohx al. The most Mesethmoid dorsal ray is flattened and is closely attached to the lower side of the opercular and interopercular. The three medial rays are considerably shorter than the other rays. The urohyal (Fig. 161) is an unpaired bone attached to the posterior edge of the hypohyals and extending posteriorly beneath the anterior branchial arches. The urohyals of 713 fish species are described by Kusaka (1974) including those of several Siluriformes. The opercular series (Fig. 158) has only three bones, the opercular, interopercular, and pre- opercular. The opercular is flat and triangular, and it articulates with the hyomandibular. The interopercular is much smaller and is located be- tween the hyomandibular, epihyal, and opercular. The preopercular has been previously mentioned as part of a lateral plate containing the hypomandi- bular and adjacent bones. The preopercular sur- rounds part of the preoperculomandibular lateral- line canal. Branchial region. Portions of five branchial arches are present but only the anterior four bear gills. The various bones present in these arches are the basibranchials, hypobranchials, cerato- branchials, epibranchials, and pharyngobranchials (Fig. 162), but not all arches contain all of these. The bones present in each arch are indicated in Table 4. The basibranchials are unpaired and are associated with the arch with which their anterior end articulates. The pharyngobranchials are also a member of the arch with which their anterior ends articulate. Considerable cartilage is present around the bones forming the floor of the pharynx. The pharyngeal teeth (Fig. 162) are located in the posterior pharynx and are associated with the posterior branchial arches. The lower teeth are present on the lower pharyngeal (hypopharyn- geal) which is completely fused to the fifth ceratobranchial. The upper teeth are located on a disc-shaped upper pharyngeal (epipharyngeal) which is attached to the pharyngobranchial and epibranchial of the third arch and the epibranchial of the fourth arch. The gill filaments (Chapter 11) are located on the ceratobranchials and epibranchials of the four anterior arches. Bony gill rakers are also present on the ceratobranchials and epibranchials. Vertebral Column and Ribs Most of the vertebrae are similar to those found in most teleosts. However, the five anterior verte- brae are highly modified to form the Weberian apparatus which is the characteristic common to all ostariophysian fishes. The unmodified verte- brae vary structurally in different parts of the verte- bral column. Although the vertebrae can be classi- fied as caudal or trunk, each vertebra is different. Particularly distinctive vertebrae are found near the Weberian apparatus, in the transitional zone between the caudal and trunk region, and near the caudal fin. CAUDAL VERTEBRAE Each of these vertebrae has an amphicoelous centrum surrounding the notochord. Pre- and post-zygopophyses on the centrum increase the area of contact between adjacent vertebrae. A neural arch which continues dorsally as the neural spine (Fig. 157) is firmly attached to the dorsal surface of the centrum. The spinal cord lies with- in the neural arches. Hemal arches extend from the ventral surface enclosing the caudal artery and continues ventrally as the hemal spine (Fig. 157). TRUNK VERTEBRAE AND RIBS These vertebrae have centra similar to caudal vertebrae but do not have hemal spines. Neural arches and spines are present, but the neural spines ventral to the dorsal fins are bifid for articulation with the pterygiophores supporting the fin. Hemal arches are absent except for the transitional pos- terior trunk vertebrae. Transverse processes (parapophyses) extend laterally from most trunk vertebrae. Nine to 11 of the vertebrae bear pleural ribs (Fig. 157). Epipleural ribs and intermuscular bones are ab- sent. The upper surface of the proximal portion of the rib articulates with the lower surface of the transverse process. The sixth vertebra is the most anterior one with ribs since the five anterior verte- TABLE 4. BONES PRESENT IN THE BRANCHIAL ARCHES OF CHANNEL CATFISH , nha rhBones of the branchial arches Branchial arch - Basibranchial Hypobranchial Ceratobranchial Epibranchial Pharyngobranchial first present present present present second present present present present present third present present present fourth present present fifth present 79 Premaxilla Max illa Branchiostegal rays yer4' Cr wlhator FIG. 161. Ventral view of the skull, anterior vertebrae, and pectoral girdle. s0 A Epihyal Interhyal Interopercular Dentary Joint Pterygoid Quadrate Hyomandibular Preopercular Pharyngobranchials Upper pharyngeal Opercular Lower pharyngeal B Branchial region Epibranchials FIG. 162. (A) Dorsal view of the branchial arches, hyoid arch, and lower jaw. Most gill rakers were omitted from the second, third, and fourth arches; (B) Dorsolateral view of the skull with mouth open to expose the branchial arches; (C) Posterior view of the right upper pharyngeal bone; (D) Ventral view of the right upper pharyngeal bone. 81 brae are modified in conjunction with the Weber- ian apparatus. The absence of ribs from the anterior vertebrae results in an area of the body cavity which is not enclosed by ribs. The lateral cutaneous area is formed in the dorsal portion of this region where muscle is also absent. The anterior chamber of the swim bladder is in direct contact with the skin in this location. WEBERIAN APPARATUS The development and anatomy of the Weberian apparatus of the channel catfish was described by Al-Rawi (1967). This modification of the anterior vertebrae connects the swim bladder to the ear to increase the sensitivity to sound. Additional discussion of the Weberian apparatus is in Chap. 9. The anterior vertebrae are fused to form the pars sustentaculum which supports the pars auditum consisting of small ossicles which de- velop from the vertebrae. Pars sustentaculumn. The second, third, and fourth vertebrae are fused into a complex vertebrae (Fig. 161) in which no clear demarcation between verte- brae can be found. The first vertebrae and fifth vertebrae are firmly united to the complex verte- bra. A deep groove present on the ventral surface of the complex, first, and fifth vertebrae contains the dorsal aorta. A broad plate extends laterally from the complex vertebrae covering the dorsal surface of the swim bladder. A dorsoposteriorly projecting process from the complex vertebrae (Fig. 158) aids in the support of the dorsal fin and a dorsoanteriorly projecting process is at- tached to the skull. Pars auditum. A chain of ossicles is present on each side of the pars sustentaculum. Each set of ossicles is composed of a tripus, intercalarium, scaphium, and claustrum (Fig. 129). The tripus, largest of the ossicles, connects firmly to the swim bladder near the middle of the complex vertebra and extends anteriorly to the first vertebra (Fig. 161). The interossicular ligaments connect the tripus to the intercalarium and the intercalarium to the scaphium. The scaphium contacts the sinus impar of the ear enabling sound received by the swim bladder to be conducted to the ear. The claustrum is also in direct contact with the sinus impar but is not directly involved in the conduc- tion of sound. Fins All of the fins are supported by skeletal elements except for the adipose fin. The histological struc- ture of fins is discussed in Chap. 7. ANAL FIN This fin (Fig. 157) is similar to the medial fins of most teleosts. The fin contains 24 to 30 lepi- dotrichia (soft rays) which articulate at the base of the fin with pterygiophores projecting between the hemal spines to which they are loosely con- nected. The, two anterior lepidotrichia articulate with one pterygiophore, and the two posterior lepidotrichia articulate with one pterygiophore so that there are two more lepidotrichia than ptery- giophores. Each lepidotrichia is composed of bilateral elements which separate basally to articu- late with the lateral surfaces of the pterygiophore. DORSAL FIN The anterior lepidotrichia and pterygiophores are highly modified to form a defensive spine and locking mechanism (Fig. 158 and 159). This fin is also firmly attached to the skull through a con- nection to the supraoccipital and the complex vertebrae. Six unmodified rays are posterior to the spine. The pterygiophores of these rays have anteriorly and posteriorly projecting bony plates which interconnect the pterygiophores. Except for the posterior pterygiophore which supports the posterior two rays, these supporting elements reach to the short bifid neural spines to which they are attached. The spine is supported by a nuchal shield formed by the posterior projection of the supra- occipital and the first three pterygiophores (Greg- ory, 1933). The two pterygiophores which extend ventrally from the spine are greatly enlarged and firmly united to the posterior neural spine of the complex vertebra. The defensive spine seems to be the highly modified second lepidotrichia with the first lepidotrichia reduced to a small locking device lying on the anterior surface of the base of the spine (Bertin, 1958b). McMurrich (1884b) presented developmental evidence that the spine represented the third ray, the locking device the second, and the anterior portion of the horizontal plate represented the first ray. The spine of the dorsal fin can be locked into an erect position by the U-shaped locking ray at its base (Fig. 159). Locking occurs when the locking ossicle slides anteriorly and ventrally over the dorsal extremity of the underlying pterygio- phore so that it is held in the erect position by the surrounding bone. The locking ossicle is firmly connected to the anterior surface of the spine by 82 a strong ligamnt so that the lockin g of the sinai I ossicle also) loceks the Spille ill ain crcct 1 )osi tio ii CAUDAL FIN The terminology used to describ~e the ecinits of the candal fill is that used( byi Lii udi ici and Baskin ( 1969 ). The lepidotrichia articuilate wxith ])oil\ plates and spines .vhich develop f romt the postel 101 caudlal v erteb~rae ( Fig. 157). The last caii dal verteb~rae is higly mnodified anid dcx (101) h(11 the first preut al and first uiral centi a (Ltn(11 or and Baskin, 1969). The hetnal spine of' the cm pound x'etrebra is modified to formn a park ~pi ral which is ventral to six hy 1)111als. D~orsal to t lie hypurals is a nriotteutal. Onc cpu ral is pre-(senIt atid lies ahove the ieuiral arch of t lie colt pomiid x (Ftc bra. The pat h\pural, the twxo x entral hI )iii-Ils and the uroneural are fused to the coinpoI ild vertebra. lin addition to the suipports associatedl with the compound verteb~ra, sev eral x ertch)1ae anterior to it haxve lengthened neural andl hetnal spines which support the dlorsal and ventral por- tions of the finl. PECTORAL FIN The pectoral girdIle supporting this fill is ms sixve and firmly attached to the skill byv the p)ost- temporal bone ( Fig. 1.58). The cleithrum and coracoid are firmnly joined to 'gether, and the stittit between these b)ones canl he scen only onl x(,Irx wvell cleanedi specimecns. The cleithera andi cora I coids of each sidle join mnidx ettrally an(1 cover the heart regJion. The coracoids haxve anl elaborate dovetailed su~ture where they join lbut thle Cleithr-a do nut (Fig. 161). The supracleithi um, scapula, and postcleithrumn are ab~sent. The fin is composed of nine unmodified lepi- dotrichia and a bony spine similar to the spine in the dorsal finl. Two radials are present b~etxxeen the pectoral girdle and the unmodified rays. The spine articulates in a deep socket of the girdle and can be locked iii anl extended position by a slight rotation. PELVIC FIN The pelvic girdle is composed of two basip- terygia which are not attached to any other ele- ment of the skeletal system (Fig. 157). The hasipterygia tend to fuse at the mnidline in adults. Eight lepidotrichia articulate with each basiptery- gium. A horse-shoe shaped cartilage projects pos teriorly from the pelvic girdle so that a cartilagin- ous process lies onl each side of the anus. Tissues of the Skeletal Sx steinl BONE I istogeneisis of bone occurs inl txxo wvaxs, and this differenlce is oltet i apparenit ill sectiot 5 of smnall fitigerlitigs. D~irect bonle flrIllationl res'lts in dermal (memnbranec) botie fl nd inl associattoi xvith the derinis. I ndit et ]l)Ot f ortnatiotn is the peticholmtdtal ossificatiotn of' lixalitie cartilage. Thec skeletal elettieitt is ptefortiid iti catrtilage, at (I this core of cartilage slirroi cld b\x 1])oil is (1is- tinctix c ( Fig. 16:3) . Pt odlitioti of botie h\i osteo- blasts atl 1( dstriactiotl 1Ix osteoclasts restIdt in g inl recntod(clitg of, botie stilictili ill somie telcosts .seems simtilar to that of, Inlatitlials (Lope/. 9-M). Bone is laintated ( Fig. 16 1 aiid 1(55) x\ itli soite b)ones Lax itig a s~oig(\ appearaticc (lue to timitlr oils spaces. The spaces xx itililtile bonec cotitattis blood x essels and1 arecola cotitiectix tissuec. Henopoictic tissuec is n ot ptr(sent x\ itliit atix. honies. NOTOCIIORI) This uiqii ue tissue is located ili the cen ter of' the centra of' the x crtebrae ( Fig'(. 166) and is imitch more prominent in jux cii les that i in ad ults. The notochord is compressed b\ each x etrcbrac atnd expandls near the junctiotn of adjacent x cit (lrac. The strttitre of notochord is unlike thiat of' bonle or cartilage because the Ii tati ix is in trace 1 i lar. Onlly thet Ccll inetlrat t atnd liitei of, the t toto- chordal cells ar-c x isilc itl histological sc-t 1011 (Fig. 16.5 ). The notochiord is siarrot tided b\ sheaths ( Patt and Patt, 1969 ) xwhich are sutr- rounded by the xvertelbral cetitra. ILYALINE CARTIILAGE This tissue forms a large p~ortion of the skeletn - - FIG. 16:3. Perichondral bone formiation is characterized by the formation of bone (B) around a cartilaginous template (C). In fingerlings, bones which are formed by this indirect process have a central core of hs aline cartilage. The bone in this figure is a rib fromi a 65 mmn TL fingerling. Bouin's; 11 & E; X 120. FIG. 164. Bone fromt the skull of at juenile has osteocvtes (0) in lacuinae antd c.alcified matrix (NI) arranged in lanmellae. L acuntae ate jprobabls connec ted b% canals loc ated betwe en hotis lameic itc. M ost hot te hac nuemtnerou s spaces (S ) contain - ng loose conti l se tissue and blood( v essels, but bone marrow is tnot present. Bounts; If & E; X 160. N BI FIG( . 165. Bone comnposinug tlhe cent t li of a N cr1 eb ra (B) is similar to that in other regions of the body . It sutiroundtis the niotochiord(lN). Boomns; 11 & 1': :320. in small fin gcrlin gs, and se\ eral par ts of the adunlt skeleton remain cartilacrinious. The chondrocytes are separated 1)\ variable amounts of clear matrix (Fig 6. 167 ). This tissue is x, crv similar to the hiva- line cartilag(' of other x ertclbrates. PSEUI)OC ARTILAGE Pseudocartilage is found ondy in the baroels (Fig. 168 and 126) and in strips attached to) the fnterlnandlilularis posterior muiscles ( Fig. 96). These strips of pseudocartilagre are attached to the mental and mandlibnlary barbels. The term pseudocartilage itatts,]by Bertin (98)t describe this tissue. GILL-FILANMENT CARTILAGE This tissue type is found only in the filaments o~f the gills and is prob~aly the same as the cartilage with Capsular strorna which Bertin ( 1958c) men- IG. 166i. Sagittal section of notochord (N). ' ertebrac WV), dforsalI aorta ( A) and~ spinal cord (S) from a juvetnile. N oto- chord is comp)osed of large turgesent cells in which a s aculole has displaed~ the contents of the cell. IThe s ertehrae coin- press the notochord givinog it an lour-glass shape. Boomns; I I & E; X 32. -, -. 4 4 4 4 I IC. 167. 1Ilvaline cartilage from the skull of a fingerling has liondfroes tes (C) which are located in lacunae sWtuoutided bv a s ri able amnount of interstitial matrix. Perichondriumn (I~ surrounds tltis cartiag wh t iche is re pla.ced by bone in the adult. Boitin's: \fasson's; x 160. cI 1 1, ,, f 1* I- 4, F IG. 168. Pseudocartilage of the barbel is composed of large os al cells Is ing close together ss ith a homogenous interstitial m atrix. Nutclei are ov al. small, and usually located near the pertiphtery of the cell. Boomns: 11 & E; X 240. tioiis being found in gill filaments. There is less matrix between cells than in hyaline cartilage, and the matrix tends to be acidophilic (Fig 169, 151, and 153). CHONDROID Tissue resembling this type of cartilage is found covering the opercular bone, hypurals of the caudal fin and perhaps other locations. This tissue is composed of closely spaced, rounded cells and scattered fibers which stain green with Masson's trichrome stain (Fig. 171 and 172). This tissue is a primitive type of cartilage (Patt and Patt, 1969). * i ~ ,"", )-d /a ~~fr 1 ~ C1,-~~ F - :k i :i;B- . b a~~~ ~B i"a"' ,~ "a~~C ~: 4 '' FIG. 171. Chondroid of the operculum. Higher magnifica- tion of area in Fig. 170. Bouin's; Masson's; X 240. FIG. 169. Cartilage of a gill filament has chondrocytes (C) which are uniformly spaced and tend to have a rectangular shape. The matrix is more acidophilic than that of hyaline cartilage. Ossification of this cartilage may occur on the mar- gins near the base of the lamellae. Bouin's; H & E; X 800. C FIG. 170. Chondroid (C) lies between the opercular bone and the skin covering the inner surface of the operculum. Chond- roid is composed of closely spaced cells with dispersed col- lagenous fibers. The skin (S) covering the inner surface of the operculum is similar to that covering the body except that alarm substance cells are absent. G, portion of gill filament. Bouin's; H & E; X 120. F; 5'"~~~"~ c I~ ~ LITERATURE CITED AL-HUSSAINI, A. H. 1947. The Anatomy and Histology of the Alimentary Tract of the Plankton-Feeder, Atherina forskali Rupp. J. Morph. 80:251-286. ALLIS, E. P. 1908. Pseudobranch and Carotid Arteries in Amneiurus. Anat. Anz. 33:256-270. AL-RAWI, A. H. A. 1967. The Development of the Web- erian Apparatus and the Swim Bladder in the Channel Catfish, Ictalurus punctatus (Rafinesque). Ph.D. Dis- sertation. Univ. Oklahoma, Norman, Oklahoma. 119 p. ANDERSON, B. G. AND D. L. MITCHUM. 1974. Atlas of Trout Histology. Wyoming Game and Fish Depart- ment, Cheyenne, Wyoming. 110 p. ANDREW, W. 1959. Textbook of Comparative Histology. Oxford Univ. Press, New York. 652 p. 1965. Comparative Hematology. Grune and Stratton, New York. 188 p. ARIENS, KAPPERS, C. U. 1906. The Structure of the Tele- ostean and Selachian Brain. J. Comp. Neurol. Psychol. 16:1-109. ----------------------- G. C. HUBER, AND E. C. CROSBY. 1936. The Comparative Anatomy of the Nervous System of Vertebrates, Including Man. The MacMillan Co., New York. 1845 p. ARNOTT, H. J., A. G. G. BEST, S. ITO, AND J. A. C. NICOL. 1974. Studies on the Eyes of Catfish with Special Ref- erence to the Tapetum Lucidum. Roy. Soc. London, Proc., B.186:13-36. ASHLEY, L. M. AND C. E. SMITH. 1963. Advantages of Tissue Imprints over Tissue Sections in Studies of Blood Cell Formation. Prog. Fish-Cult. 25:93-96. BAECHER, R. 1928. Uber die Nebennieren der Teleostier. Z. Mikrosk.-Anat. Forsch. 15:204-273. BAILEY, S. E. 1937. An Experimental Study of the Origin of Lateral-Line Structures in Embryonic and Adult Teleosts. J. Exp. Zool. 76:187-233. BAKER-COHEN, K. F. 1959. Renal and Other Heterotopic Thyroid Tissue in Fishes, p. 283-301. In A. Gorbman (ed.) Comparative Endocrinology. John Wiley and Sons, New York. BALL, J. N. 1969. Fish Prolactin and Growth Hormone, p. 207-240. In W. S. Hoar and D. J. Randall (ed.) Fish Physiology, Vol. II. Academic Press, New York. AND B. I. BAKER. 1969. The Pituitary Gland: Anatomy and Histophysiology, p. 1-111. In W. S. Hoar and D. J. Randall (ed.) Fish Physiology, Vol. II. Academic Press, New York. BANNISTER, L. H. 1965. The Fine Structure of the Ol- factory Surface of Teleostean Fishes. Quart. J. Micro- scop. Sci. 106:333-342. BARDACH, J. E., J. H. TODD, AND R. CRICKMER. 1967. Orientation by Taste in Fish of the Genus Ictalurus. Science 155:1276-1278. BENCOSME, S. A., J. MEYER, B. J. BERGMAN, AND A. MARTINEZ-PALMO. 1965. The Principal Islet of Bull- head Fish (Ictalurus nebulosus). Rev. Can. Biol. 24: 141-154. BERLIND, A. 1972. Teleost Caudal Neurosecretory Sys- tem: Sperm Duct Contraction Induced by Urophysial Material. J. Endocrinol. 52:567-574. . 1973. Caudal Neurosecretory System: A Physiologist's View. Amer. Zool. 13:759-770. BERN, H. A. 1969. Urophysis and Caudal Neurosecretory System, p. 399-418. In W. S. Hoar and D. J. Randall (ed.) Fish Physiology, Vol. II. Academic Press, New York. BERNSTEIN, J. J. 1970. Anatomy and Physiology of the Central Nervous System, p. 1-90. In W. S. Hoar and D. J. Randall (ed.) Fish Physiology, Vol. IV. Aca- demic Press, New York. BERTIN, LEON. 1958a. Appareil Circulatorie, p. 1399- 1458. In P.-P. Grass6 (ed.) Trait6 de Zoologie, Vol. 13, Part 1. Mason, Paris. . 1958b. Modifications des Nageoires, p. 748-782. In. P.-P. Grass (ed.) Trait6 de Zoologie, Vol. 13, Part 1. Mason, Paris. .. 1958c. Tissus Squelettiques, p. 532-550. In P.-P. Grass6 (ed.) Trait6 de Zoologie, Vol. 13, Part 1. Masson, Paris. BIRKHEAD, W. S. 1967. The Comparative Toxicity of Stings of the Ictalurid Catfish Genera Ictalurus and Schilbeodes. Comp. Biochem. Physiol. 22:101-111. BLOOMI, W. AND D. W. FAWCETT. 1975. A Textbook of Histology. 10th ed. W. B. Saunders Co., Philadelphia. 1033 p. BRAEKEVELT, C. R. AND D. B. MMILLAN. 1967. Cyclic Changes in the Ovary of the Brook Stickleback, Eucalia inconstans (Kirkland). J. Morph. 123:373-396. BRANSON, B. A. 1966. Guide to the Muscles of Bony Fishes, Excluding Some Special Fibers in Siluroids and a Few Others. Turtox News 44:98-102. AND G. A. MOORE. 1962. The Lateralis Components of the Acoustico-Lateralis System in the Sunfish Family Centrarchidae. Copeia 1962:1-108. BRETSCHNEIDER, L. H. AND J. J. DUYVENE DE WIT. 1947. Sexual Endocrinology of Non-Mammalian Vertebrates. Elsevier, New York. 146 p. BRINN, J. E. JR. 1971. The Pancreatic Islet Cells of the Channel Catfish, Ictalurus punctatus. Anat. Rec. 169: 284. .1973. The Pancreatic Islets of Bony Fishes. Amer. Zool. 13:653-665. BULGER, R. E. AND B. F. TRUMP. 1968. Renal Morphol- ogy of the English Sole (Parophrys vetulus). Amer. J. Anat. 123:195-226. CALOVICH, F. E. AND B. A. BRANSON. 1964. The Su- praethmoid-ethmoid Complex in the American Cat- fishes, Ictalurus and Pylodictis. Amer. Midl. Nat. 71: 335-343. CAMACHO, A. S. 1974. Characterization of Thiamine De- ficiency in Channel Catfish (Ictalurus punctatus, Ra- finesque) Fed Heated and Non-Heated Catfish Proces- sing Waste. Ph.D. Dissertation. Auburn University, Auburn, Alabama. 75 p. CAMPBELL, G. 1970. Autonomic Nervous System, p. 109- 132. In W. S. Hoar and D. J. Randall (ed.) Fish Physiology, Vol. IV. Academic Press,. New York. CAPRIO, J. AND R. RADERMAN-LITTLE. 1978. Scanning Electron Microscopy of the Channel Catfish Olfactory Lamellae. Tissue Cell 10:1-9. CATTON, W. T. 1951. Blood Cell Formation in Certain Teleost Fishes. Blood 6:39-60. 86 CHAKRABARTE, J., R. SAHARYA, AND D. K. BELSARE. 1973. Structure of the Gall Bladder in Some Freshwater Teleosts. Z. Mikrosk.-Anat. Forsch. 87:23-32. CHESTER JONES, I., D. K. O. CHAN, I. W. HENDERSON, AND J. N. BALL. 1969. The Adrenocortical Steroids, Adren- ocorticotropin and the Corpuscles of Stannius, p. 321- 376. In W. S. Hoar and D. J. Randall (ed.) Fish Physi- ology, Vol. II. Academic Press, New York. CLARK, S. L., M. Y. CHUNG, L. SHINE, AND M. R. CLARK. 1960. Responses in Free Swimming Fishes to Electri- cal Stimulation of the Cerebellum. Amer. J. Anat. 106:121-132. CLEMENS, H. P. AND K. E. SNE. 1957. The Spawning Behavior of the Channel Catfish Ictalurus punctatus. U.S. Fish and Wildl. Serv., Spec. Sci. Rep. Fish. No. 219. 11 p. COMBS, R. M. 1969. Embryogenesis, Histology and Or- ganology of the Ovary of Brevoortia patronus. Gulf Res. Rep. 2:333-434. COOPER, L. J. 1952. A Histological Study of the Repro- ductive Organs of Crappies (Pomoxis nigromaculatus and Pomoxis annularis). Amer. Microscop. Soc., Trans. 71:393-404. COPP, D. H. 1969. The Ultimobranchial Glands and Cal- cium Regulation, p. 377-398. In W. S. Hoar and D. J. Randall (ed.) Fish Physiology, Vol. II, Academic Press, New York. CROss, F. B. 1967. Handbook of the Fishes of Kansas. Univ. Kan. Mus. Nat. Hist., Misc. Publ. 21. 156 p. CuccHI, C. 1969. Il Sistema Neurosecernente Caudale del l'Ictalurus sp. (Teleosteo Ictaluride): Sviluppo e Variazioni Stagionali. Acad. Nat. dei Lincei, Rendi- conti. 47:365-370. CURRY, E. 1939. The Histology of the Digestive Tube of the Carp (Cyprinuts carpio communis). J. Morph. 65: 53-78. DAMMERMANN, K. W. 1910. Der Saccus Vasculosus der Fische ein Tieforgan. Z. Wiss. Zool. 96:654-726. DESGRANGES, J. L. 1965. Sur l'existence de Plusieurs Types de Cellules Sensorielles danses Bourgeons du DIJKGRAAF, S. 1962. The Functioning and Significance of the Lateral-line Organs. Biol. Rev. 38:51-105. DIXIT, V. P. 1970. Histophysical Studies of the Interrenal Gland in Clarias batrachus (Linn.). Acta Anat. 77: 310-318. .....------ . 1971. The Karyometric Response of the Caudal Neurosecretory Cells in Clarias batrachus to Sex Steroids. Gen. Comp. Endocrinol. 17:561-563. DODGEN, C. L. AND S. SULLIVAN. 1969. Hematological Effects of Apholate on Channel Catfish (Ictalurus punctatus). Soc. Exp. Biol. Med., Proc. 181:124-126. EASTMAN, J. T. 1971. The Pharyngeal Bone Musculature of the Carp, Cyprinus carpio. J. Morph. 184:131-140. EATON, T. H. 1948. Form and Function in the Head of Channel Catfish, Ictalurus lacustris punctatus. J. Morph. 88:181-194. EDGEWORTH, F. H. 1935. The Cranial Muscles of Verte- brates. Cambridge Univ. Press, London. 498 p. EDWARDS, J. G. AND C. SCHNITTER. 1933. The Renal Unit in the Kidney of Vertebrates. Amer. J. Anat. 53:55-87. EPPLE, A. 1967. A Staining Sequence for A, B, and D Cells of Pancreatic Islets. Stain Technol. 42:58-61. -----.. 1969. The Endocrine Pancreas, p. 275-319. In W. S. Hoar and D. J. Randall (ed.) Fish Physiology, Vol. II. Academic Press, New York. AND T. L. LEWIS. 1973. Comparative Histo- physiology of the Pancreatic Islets. Amer. Zool. 13: 567-590. EULER, U. S. VON. 1963. Chromaffin Cell Hormones, p. 258-290. In U. S. von Euler and H. Heller (ed.) Com- parative Endocrinology, Vol. I. Academic Press, New York. FENWICK, J. C. 1970a. The Pineal Organ, p. 91-108. In W. S. Hoar and D. J. Randall (ed.) Fish Physiology, Vol. IV. Academic Press, New York. S- . 1970b. Demonstration and Effect of Mel- atonin in Fish. Gen. Comp. Endocrinol. 14:86-97. -.. 1970c. Effects of Pinealectomy and Bi- lateral Enucleation on the Phototactic Response and on the Conditioned Response to Light of the Goldfish, Carassius auratus. Can. J. Zool. 48:175-182. FLOCK, A. 1971. The Lateral Line Organ Mechanorecp- tors, p. 241-263. In W. S. Hoar and D. J. Randall (ed.) Fish Physiology, Vol. V. Academic Press, New York. FONTAINE, M. 1967. Intervention des Corpuscles de Stan- nius dans l'Equilibre Phosphocalcique du Milieu In- terieur d'un Poisson Teleosteen, l'Anguille. Compt. Rend. Acad. Sci. Paris. 264:736-737. FORSTER, R. P. AND L. GOLDSTEIN. 1969. Formation of Excretory Products, p. 313-350. In W. S. Hoar and D. J. Randall (ed.) Fish Physiology, Vol. I. Academic Press, New York. GAMMON, R. L. 1970. The Gross and Microanatomy of the Digestive Tract and the Pancreas of the Channel Catfish, Ictalurus punctatus. M.S. Thesis. Kansas State Univ., Manhattan, Kansas. 52 p. GOODRICH, E. S. 1930. Studies on the Structure and De- velopment of Vertebrates. Reprint by Dover Publ. Inc., New York, 1958. 2 Vol. GORBMAN, A. 1969. Thyroid Function and its Control in Fishes, p. 241-274. In W. S. Hoar and D. J. Randall (ed.) Fish Physiology, Vol. II. Academic Press, New York. - - AND H. A. BERN. 1966. A Textbook of Com- parative Endocrinology. John Wiley and Sons Inc., New York. 468 p. GOTTFRIED, H. AND P. J. VAN MULLEM. 1967. On the Histology of the Interstitium and the Occurrence of Steroids in the Stickleback (Gasterosteus aculeatus L.) Testis. Acta Endocrinol. 56:1-15. GREENE, C. W. 1913. An Undescribed Longitudinal Dif- ferentiation of the Great Lateral Muscle of the King Salmon. Anat. Rec. 7:99-101. .. .- AND C. H. GREENE. 1913. The Skeletal Musculature of the King Salmon. Bull. Bur. Fisheries. 33:25-59. GREGORY, W. K. 1933. Fish Skulls. A Study of the Evo- lution of Natural Mechanisms. Amer. Phil. Soc., Trans. 23:75-481. GROVER-JOHNSON, N. AND A. I. FARBMAN. 1976. Fine Structure of Taste Buds in the Barbel of the Catfish, Ictalurus punctatus. Cell Tissue Res. 169:395-404. HAFEEZ, M. A. 1971. Light Microscope Studies on the Pineal Organ in Teleost Fishes with Special Regard to its Function. J. Morph. 134:281-814. 87 HAIDER, G. 1968. Vergleichende Untersuchungen zur Blutmorphologie und Hamatopoese Einiger Teleostier. III Beobachtungen an Leukozyten und Plasmazellen. Zool. Anz. 180:110-180. HANN, H. W. 1927. The History of the Germ Cells of Cottus bairdii Girard. J. Morph. 43:427-497. HARA, T. J. 1971. Chemoreception, p. 79-120. In W. S. Hoar and D. J. Randall (ed.) Fish Physiology, Vol. V. Academic Press, New York. HARRIS, G. G. AND W. A. VAN BERGEIJK. 1962. Evidence that the Lateral Line Organ Responds to the Nearfield Displacements of Sound Sources in Water. J. Acoust. Soc. Amer. 34:1831-1841. HAws, T. G. AND C. J. GOODNIGHT. 1962. Some Aspects of the Hematology of Two Species of Catfish in Rela- tion to Their Habitats. Physiol. Zool. 35:8-17. HERRICK, C. J. 1901. The Cranial Nerves and Cutaneous Sense Organs of the North American Siluroid Fishes. J. Comp. Neurol. 11:177-249. .-........ 1905. The Central Gustatory Paths in the Brains of Bony Fishes. J. Comp. Neurol. 15:375-456. HICKMAN, C. P. JR. AND B. F. TRUMP. 1969. The Kidney, p. 91-240. In W. S. Hoar and D. J. Randall (ed.) Fish Physiology, Vol. I. Academic Press, New York. HINTON, D. E. AND C. R. POOL. 1976. Ultrastructure of the Liver in Channel Catfish Ictalurus punctatus (Ra- finesque). J. Fish Biol. 8:209-219. HISAw, F. L. AND A. ALBERT. 1947. Observations on the Reproduction of the Spiny Dogfish, Squalus acanthias. Biol. Bull. 92:187-199. HOAR, W. S. 1955. Reproduction in Teleost Fishes. Mem. Soc. Endocrinol. 4:5-24. - 1957. Endocrine Organs, p. 245-286. In M. E. Brown (ed.) The Physiology of Fishes, Vol. I. Academic Press, New York. .-----------------. 1965. Comparative Physiology: Hormones and Reproduction in Fishes. Ann. Rev. Physiol. 27: 51-70. _. 1969. Reproduction, p. 1-72. In W. S. Hoar and D. J. Randall (ed.) Fish Physiology, Vol. III. Aca- demic Press, New York. HUGHES, G. M. 1966. The Dimensions of Fish Gills in Relation to Their Function. J. Exp. Biol. 45:177-195. -- AND A. V. GRIMSTONE. 1965. The Fine Structure of the Secondary Lamellae of the Gills of Gadus pollachius. Quart. J. Microscop. Sci. 106:343- 353. HUMASON, G. L. 1967. Animal Tissue Techniques. 2nd ed. W. H. Freeman and Co., San Francisco. 569 p. HURLEY, D. A. AND K. C. FISHER. 1966. The Structure and Development of the External Membrane in Young Eggs of the Brook Trout, Salvelinus fontinalis (Mit- chill). Can. J. Zool. 44:173-190. HYMAN, L. H. 1942. Compartive Vertebrate Anatomy. 2nd ed. Univ. of Chicago Press, Chicago. 544 p. JAKOWSKA, SOPHIE. 1956. Morphologie et Nomenclature des Cellules du Sang des Teleosteens. Rev. Hematol. 11:519-539. JAMES, M. F. 1946. Histology of Gonadal Changes in the Bluegill, Lepomis macrochirus, Rafinesque, and the Largemouth Bass, Huro salmoides (Lac~pbde). J. Morph. 79:63-91. JASPERS, E. J., J. W. AVAULT, JR., AND J. D. ROUSSEL. 1976. Spermatozoal Morphology and Ultrastructure of Chan- nel Catfish, Ictalurus punctatus. Trans. Amer. Fish. Soc. 105:475-480. JEARLD, A. JR. 1970. Fecundity, Food Habits, Age and Growth, Length-weight Relationships and Condition of Channel Catfish, Ictalurus punctatus (Rafinesque), in a 3300 Acre Turbid Oklahoma Reservoir. M.S. Thesis, Oklahoma State Univ., Stillwater, Oklahoma. 78 p. JENKINS, D. B. 1977. A Light Microscopic Study of the Saccule and Lagena in Certain Catfish. Amer. J. Anat. 150:605-630. JOHNSON, D. E., J. L. TORRENCE, R. P. ELDE, G. E. BAUER, B. D. NOE, AND D. J. FLETCHER. 1976. Immunohisto- chemical Localization of Somatostatin, Insulin and Glucagon in the Principal Islets of the Anglerfish (Lo- phius americanus) and the Channel Catfish (Ictalurus punctata). Amer. J. Anat. 147:119-124. JOLLIE, W. P. AND L. G. JOLLIE. 1964. The Fine Structure of the Ovarian Follicle of the Ovoviviparous Poeciliid Fish, Lebistes reticulatus I. Maturation of Follicular Epithelium. J. Morph. 114:479-502. JONES, F. R. H. AND N. B. MARSHALL. 1953. The Structure and Function of the Teleostean Swimbladder. Biol. Rev. Cambridge Phil. Soc. 28:16-83. JORDAN, D. S., B. W. EVERMANN, AND H. W. CLARK. 1930. Check List of the Fishes and Fishlike Vertebrates of of North and Middle America North of the Northern Boundary of Venezuela and Colombia. Appendix X to the Report of the U.S. Commissioner of Fisheries for 1928. USDI. Fish and Wildlife Service, Washing- ton, D.C. JORDAN, H. E. AND C. C. SPEIDEL. 1924. Studies on Lym- phocytes. II. The Origin and Fate of Lymphocytes in Fishes. J. Morph. 38:529-546. KENDALL, M. W. AND W. E. HAWKINS. 1975. Hepatic Morphology and Acid Phosphatase Localization in the Channel Catfish (Ictalurus punctatus). J. Fish. Res. Board Can. 32:1459-1464. .................... AND D. E. HINTON. 1974. Renal Tubu- lar Morphology in the Channel Catfish (Ictalurus punctatus) Kidney. J. Fish. Res. Board Can. 31:346- 347. KHANNA, S. S. AND H. R. SINGH. 1967. Histology and Histochemistry of the Saccus Vasculosus in Some Tele- osts (Pisces). Acta Anat. 67:304-311. KINDRED, J. E. 1919. The Skull of Amniurus. Illinois Biol. Monogr. 5:1-122. Reprint by Johnson Reprint Corp., New York, 1967. KLEEREKOPER, H. AND P. A. ROGGENKAMP. 1959. An Ex- perimental Study on the Effect of the Swimbladder on Hearing Sensitivity in Ameiurus nebulosus nebulosus (Leiueur). Can. J. Zool. 37:1-8. KREMENTZ, A. B. AND G. B. CHAPMAN. 1975. Ultrastruc- ture of the Posterior Half of the Intestine of the Chan- nel Catfish, Ictalurus punctatus. J. Morph. 145:441- KRISHNAMURTHY, V. G. 1968. Histochemical and Bio- chemical Studies of the Corpuscles of Stannius of the Teleost Fish Colisa lalia. Gen. Comp. Endocrinol. 11: 92-103. KUBOTAKI, M. 1961. The Microscopic Studies of the Epithelium of Saccus Vasculosus in Teleosts. Acta Anat. Nippon. 36:277-288. 88 KUSAKA, TAKAYA. 1974. The Urohyal of Fishes. Univ. of Tokyo Press, Tokyo. 319 p. LAGLER, K. F., J. E. BARDACH AND R. R. MILLER. 1962. Ichthyology. John Wiley and Sons, Inc., New York. 545 p. LAMBERT, J. G. D. AND P. G. W. J. VAN OORDT. 1965. Preovulatory Corpora Lutea or Corpora Atretia in the Guppy, Poecilia reticulata. A Histological and Histo- chemical Study. Gen. Comp. Endocrinol. 5:693-694. LANE, W. L. 1973. Investigations on the Proteolytic Di- gestive Enzymes of the Channel Catfish, Ictalurus punctatus (Rafinesque) and White Amur, Ctenopharyn- godon idella (Valenciennes). M.S. Thesis. Auburn Univ., Auburn, Ala. 38 p. LE DANOIS, Y. 1958. Systeme Musculaire, p. 783-817. In P.-P. Grass6 (ed.) Traite de Zoologie, Vol. 13, Part 1. Masson, Paris. LICHT, J. H. AND W. S. HARRIS. 1973. The Structure, Composition and Elastic Properties of the Teleost Bul- bus Arteriosus in the Carp, Cyprinus corpio. Comp. Biochem. Physiol., B. 46:699-708. LIEM, K.-F. 1967. Functional Morphology of the In- tegumentary, Respiratory, and Digestive Systems of the Synbranchoid Fish Monopterus albus. Copeia 1967:375-388. LILEY, N. R. 1969. Hormones and Reproductive Behavior in Fishes, p. 73-116. In W. S. Hoar and D. J. Randall (ed.) Fish Physiology, Vol. I. Academic Press, New York. LOPEZ, E. 1970. L'os Cellulaire d'un Poisson Teleosteen "Anguilla anguilla L." II. Action de L'ablation des Corpuscules de Stannius. Z. Zellforsch 109:566-572. LOWENSTEIN, 0. 1971. The Labyrinth, p. 207-240. In W. S. Hoar and D. J. Randall (ed.) Fish Physiology, Vol. V. Academic Press, New York. LUNDBERG, J. G. AND J. N. BASKIN. 1969. The Caudal Skeleton of the Catfishes, Order Siluriformes. Amer. Mus. Novitates 2398:1-49. MACALLUM, B. A. 1884. Alimentary Canal, Liver, Pan- creas, and Air-bladder of Amiurus catus. Proc. Can. Inst. n.s.2:387-417. MANSUETI, A. J. AND J. D. HARDY JR. 1967. Development of Fishes of the Chesapeake Bay Region, Part I. Univ. of Maryland Natural Resources Institute, College Park, Maryland. 202 p. MARSHALL, A. J. AND B. LOFT. 1956. The Leydig-cell Homologue in Certain Teleost Fishes. Nature 177: 704-705. MATTHEWS, S. A. 1938. The Seasonal Cycle in the Gonads of Fundulus. Biol. Bull. 75:66-74. MCKENZIE, T. 1884. The Blood Vascular System, Duct- less Glands, and Uro-genital System of Amiurus catus. Proc. Can. Inst. n.s. 2:418-443. McMURRICH, J. P. 1884a. The Myology of Amiurus catus (L.) Gill. Proc. Can. Inst., n.s. 2:311-351. .. . . . 1884b. The Osteology of Amiurus catus (L). Gill. Proc. Can. Inst. n.s. 2:270-310. MCVAY, J. A. AND H. W. KAAN. 1940. The Digestive Tract of Carassius auratus. Biol. Bull. 78:53-67. MEHROTRA, B. K. AND S. S. KHANN. 1969. Histomorphol- ogy of the Oesophagus and the Stomach in Some Indian Teleosts with Inference on their Adaptive Fea- tures. Zool. Beitr. 15:375-391. MOEN, T. 1959. Sexing of Channel Catfish. Amer. Fish. Soc., Trans. 88:149. MOLLENHAUER. H. H. 1963. Plastic Embedding Mixtures for use in Electron Microscopy. J. Stain Tech. 39:111- 114. MOSER, H. G. 1967. Seasonal Histological Changes in the Gonads of Sebastodes paucispinis Ayres, an Ovovivi- parous Teleost (Family Scorpaenidae). J. Morph. 123:329-353. MULLINGER, A. M. 1964. The Fine Structure of Ampul- lary Electric Receptors for Amiurus. Roy. Soc. London, Proc., B. 160:345-359. MUNZ, F. W. 1971. Vision: Visual Pigments, p. 1-32. In W. S. Hoar and D. J. Randall (ed.) Fish Physiology, Vol. V. Academic Press, New York. NAKA, K. AND N. R. G. CARRAAY. 1975. Morphological and Functional Identifications of Catfish Retinal Neu- rons I. Classical Morphology. J. Neurophysiol. 38: 53-71. NANDI, J. 1962. The Structure of the Interrenal Gland in Teleost Fishes. Univ. Calif. Pub. Zool. 65:129-212. NEWSTEAD, J. D. 1967. Fine Structure of the Respiratory Lamellae of Teleostean Gills. Z. Zellforsch. Mikroskop. Anat. 79:396-428. NORTON, V. M., H. NISHIMURA, AND K. B. DAvIs. 1976. A Technique for Sexing Channel Catfish. Trans. Amer. Fish. Soc. 105:460-462. NURSALL, J. R. 1963. The Caudal Musculature of Hoplo- pagrus guntheri Gill (Perciformes; Lutjanidae). Can. J. Zool. 41:865-880. OGAWA, M. 1961. Comparative Study on the External Shape of the Teleostean Kidney with Relation to Phy- logeny. Sci. Rep. Tokyo Kyoiku Daigaku, B. 10:61-88. PALOUMPIS, A. A. 1964. A Key to the Illinois Species of Ictalurus (Class Pisces) Based on the Supraethmoid Bone. Illinois State Acad. Sci., Trans. 57:253-256. PANG, P. K. T. 1971. Calcitonin and Ultimobranchial Glands in Fishes. J. Exp. Zool. 178:89-100. ------------------. 1973. Endocrine Control of Calcium Metabolism in Teleosts. Amer. Zool. 13:775-792. PATT, D. I. AND G. R. PATT. 1969. Comparative Verte- brate Histology. Harper & Row, New York. 438 p. PERKS, A. M. 1969. The Neurohypophysis, p. 111-205. In W. S. Hoar and D. J. Randall (ed.) Fish Physiology, Vol. II. Academic Press, New York. PFEIFFER, W. 1960. Uber die Verbreitung der Schreck- reaktion bei Fischen. Natruwissenschaften 47:23. ................. 1962. The Fright Reaction of Fish. Biol. Rev. Cambridge Phil. Soc. 37:495-511. - . 1963. The Fright Reaction in North American Fish. Can. J. Zool. 41:69-77. . 1977. The Distribution of Fright Reaction and Alarm Substance Cells in Fishes. Copeia 1977: 653-665. PHILLIPS, J. G. AND D. BELLAMY. 1963. Adrenocortical Hormones, p. 208-257. In U. S. von Euler and H. Heller (ed.) Comparative Endocrinology. Academic Press, New York. PHILPOTT, H. C. W. AND D. E. COPELAND. 1963. Fine Structure of Chloride Cells from Three Species of Fundulus. J. Cell Biol. 18:389-401. PICKFORD, G. E. AND J. W. ATz. 1957. The Physiology of the Pituitary Gland of Fishes. New York Zool. Soc., New York. 613 p. 89 POGGENDORF, D. 1952. Die Absoluten Horschwellen des Zwergwelses (Ameiurus nebulosus) und Beitrage zur Physik des Weberschen Apparatus der Ostariophysen. Z. Vergleich. Physiol. 34:222-257. REED, H. D. 1907. The Poison Glands of Noturus and Schilbeodes. Amer. Natur. 41:553-566. . 1924a. The Morphology and Growth of the Spines of Siluroid Fishes. J. Morp. 88:431-451. . 1924b. The Morphology of the Dermal Glands in Nematognathous Fishes. Z. Morph. Anthro- pol. 24:227-264. REIFEL, C. W. AND A. A. TRAVILL. 1977. Structure and Carbohydrate Histochemistry of the Esophagus in Ten Teleostean Species. J. Morph. 152:303-314. REYNOLDS, E. S. 1963. The Use of Lead Citrate at High pH as an Electron Opaque Stain in Electron Micro- scopy. J. Cell Biol. 17:208. RIZKALLA, W. 1970. The Morphology of the Pineal Organ in the Teleost, Clarias lazera, C. V. Acta Biol. Acad. Sci. Hung. 21:25-33. ROMER, A. S. 1955. The Vertebrate Body. 2nd ed. Saun- ders, Philadelphia. 644 p. SAGE, M. 1973. The Evolution of Thyroid Function in Fishes. Amer. Zool. 13:899-905. SAMUEL, M. 1943. Studies on the Corpus Luteum in Rhinobatus granulatus Cuv. Indian Acad. Sci., Proc., B. 18:133-157. SAUNDERS, D. C. 1967. Neutrophils and Arneth Counts from Some Red Sea Fishes. Copeia 1967:681-683. SCHREIBMAN, M. P., J. F. LEATHERLAND, AND B. A. Mc- KEOWN. 1973. Functional Morphology of the Teleost Pituitary Gland. Amer. Zool. 13:719-742. SCHWASSMANN, H. O. AND L. KRUGER. 1968. Anatomy of Visual Centers in Teleosts, p. 1-16. In D. Ingle (ed.) The Central Nervous System and Fish Behavior. Univ. Chicago Press, Chicago. SHELDEN, F. F. 1937. Osteology, Myology and Probable Evolution of the Nematognath Pelvic Girdle. Ann. N.Y. Acad. Sci. 37:1-96. SHELTON, W. L. 1964. The Threadfin Shad, Dorosoma petenense (Giinther): Oogenesis, Seasonal Ovarian Changes and Observations on Life History. M.S. Thesis. Oklahoma State Univ., Stillwater, Oklahoma. 48 p. SINGH, B. R. AND J. S. D. MUNSHI. 1968. The Jaw Muscles and Their Mode of Working in Two Indian Siluroid Fishes. Zool. Anz. 181:356-370. SMITH, H. W. 1929. The Excretion of Ammonia and Urea by the Gills of Fish. J. Biol. Chem. 81:727-742. SNEED, K. E. AND H. P. CLEMENS. 1963. The Morphology of the Testes and Accessory Reproductive Glands of the Catfishes (Ictaluridae). Copeia 1963:606-611. SRIVASTAVA, A. K. 1969. Studies on the Hematology of Certain Freshwater Teleosts. V. Thrombocytes and Clotting of Blood. Anat. Anz. 124:368-374. STORCH, V. N. AND U. N. WELSCH. 1970. Electron Micro- scope Observations on the Taste-buds of Some Bony Fishes. Arch. Histol. Jap. 32:145-153. TAVOLGA, W. N. 1971. Sound Production and Detection, p. 185-205. In W. S. Hoar and D. J. Randall (ed.) Fish Physiology, Vol. V. Academic Press, New York. TAYLOR, W. R. 1967. An Enzyme Method of Clearing and Staining Small Vertebrates. Proc. United States Nat. Mus. 122:1-17. TODD, J. H., J. ATEMA, AND J. E. BARDACH. 1967. Chem- ical Communication in Social Behavior of a Fish, the Yellow Bullhead (Ictalurus natalis). Science 158:672- 673. WARGO, A. A. 1978. Light and Electron Microscope Studies of Changes in Gastric Tissues of the Channel Catfish, Ictalurus punctatus (Rafinesque), as Related to Feeding Times. Ph.D. Dissertation. Georgetown University, Washington, D.C. 258 p. WATSON, L. J., I. L. SHECHMEISTER, AND L. L. JACKSON. 1963. The Hematology of Goldfish, Carassius auratus. Cytologia 28:118-180. WATSON, M. L. 1958. Staining of Tissue Sections for Electron Microscopy with Heavy Metals. II. Applica- tion of Solutions Containing Lead and Barium. J. Biophys. Biochem. Cytol. 4:475-479. WEINBERG, S. R., C. D. SIEGAL, R. F. NIGRELLI, AND A. S. GORDON. 1972. The Hematological Parameters and Blood Cell Morphology of the Brown Bullhead Catfish, Ictalurus nebulosus (Lesueur). Zoologica 57:71-78. WEINREB, E. L. 1963. Studies on the Fine Structure of Teleost Blood Cells. I. Peripheral Blood. Anat. Rec. 147:219-238. WEINREB, E. L. AND N. M. BILSTAD. 1955. Histology of the Digestive Tract and Adjacent Structures of the Rainbow Trout, Salmo gairdneri irideus. Copeia 1955: 194-204. WEISEL, G. F. 1949. The Seminal Vesicles and Testes of Gillichthys, a Marine Teleost. Copeia 1949:101-110. WILLIAMS, R. W. AND M. C. WARNER. 1976. Some Ob- servations on the Stained Blood Cellular Elements of Channel Catfish, Ictalurus punctatus. J. Fish Biol. 9:491-497. WILLIAMS, W. L. 1960. Hepatic Liposis and Myocardial Damage in Mice Fed Choline-deficient or Choline- supplemented Diets. Yale J. Biol. Med. 33:1-4. WINGSTRAND, K. G. 1951. The Structure and Develop- ment of the Avian Pituitary from a Comparative and Functional View Point. C. W. K. Gleerup, Lund, Sweden. 816 p. .----.------------ ------ -. 1966. Comparative Anatomy and Evolution of the Hypophysis, p. 58-126. In G. W. Harris and B. T. Donovan (ed.) The Pituitary Gland, Vol. I. Butterworth, Washington, D.C. WORKMAN, I. S. 1900. The Ophthalmic and Eye Muscle Nerves of the Catfish (Ameiurus). Comp. Neurol. 10: 403-410. WRIGHT, R. R. 1884a. On the Skin and Cutaneous Sense Organs of Amiurus. Proc. Can. Inst. n.s. 2:251-269. -.---------...... 1884b. On the Nervous System and Sense Organs of Amiurus. Proc. Can. Inst. n.s. 2:352-386. YOKOYAMA, H. 0. 1960. Studies on the Origin, Develop- ment, and Seasonal Variations in the Blood Cells of the Perch, Perca flavescens. Wildl. Dis. 6:1-102. YOUNc, J. Z. 1981. The Pupillary Mechanisms of the Teleostean Fish Uranoscopus scaber. Roy. Soc. Lon- don, Proc. B. 107:464-485. YUKI, R. 1960. Blood Cell Constituents in Fish. IV. On the "Nuclear Shadow" Found in Blood Smear Prepara- tions. Bull. Jap. Soc. Sci. Fish. 26:490-495. 90 INDEX Abducens nerve, 51, 58 Abductor superficialis of pectoral fin, 46 Abductor superficialis of pelvic fin, 46 Abductor profundus of pectoral fin, 46 Abductor profundus of pelvic fin, 46 Abductor tentaculi, see Adductor arcus palatini Accessory ossicles of lateral line, 64 A-cells of pancreas, 30, 31 Acidophilic cells of gills, see Chloride cells Acini of pancreas, 14, 24-26 Acoustic nerve, 51, 58 Acousticolateralis lobe, 51, 57 Adductor arcus palatini, 47 Adductor hyomandibularis, 46, 48 Adductor mandibulae, 47 Adductor operculi, 47 Adductor profundus of-pectoral fin, 46 Adductor profundus of pelvic fin, 46 Adductor superficialis of pectoral fin, 46 Adductor superficialis of pelvic fin, 46 Adenohypophysis, 31-33 Adipose fin, 3, 40-42 Adipose tissue, 41, 42 Adrenal cortical tissue, see Interrenal tissue Adrenal gland, see Head kidney Adrenalin, 30 Adrenocorticotropic cells, 32 Adventitia, 21 Afferent arteriole of gill filament, 71, 72 Afferent branchial arteries, histology, 5, 9, 10 Air bladder, see Swim bladder Alarm substance cells, 19, 20, 39-42, 65 Alimentary canal, 19-24 Alisphenoid, 75 Alpha cells, see A-cells of pancreas Amacrine cells of retina, 60 Amniurus catus, 1, 2 Ampullae of ear, 63 Ampullary organs, see Small pit organs Anal fin, 3, 41, 82 muscles, 45 Androgen, 67 Anterior cardinal vein, 6, 9 Anterior infracarinales, 46 Anterior rectus muscle, 47, 50, 58 Anus, 3 Aorta, see Dorsal aorta and Ventral aorta Archinephric duct, see Opisthonephric duct Arrector dorsalis, 46 Arrector ventralis, 46 Arteries, gross anatomy, 5-9 histology, 8-11 Arterioles, 5 structure, 10 Articular, 47, 76-78, 80, 81 Asteriscus, 64 Atretic follicles, 70 Atrium, 11, 12, 19 Attractor arcus branchialis, 48 Autonomic nervous system, 50, 59 Axillary gland, 42 Barbels, 3, 40, 47, 61, 62, 84 Basement membrane, 36, 72 Basibranchials, 79, 81 Basioccipital, 75, 78, 80 Basipterygium, 46, 74, 83 Basophils, 15 B-cells of pancreas, 30, 31 Beta cells, see B-cells of pancreas Bile, 26, 27 Bile canaliculi, 25-27 Bile ducts, 25-27, 30 Bipolar cells of retina, 60 Black bullhead, see Ictalurus melas Bladder, see Urinary bladder Blood, cells, 12, 15-18 cell counts, 15 hematocrit, 17, 18 methods, 15 Blood pressure, 5, 13 Blood vessels, 5-11 latex injection, 5 Bone histology, 83, 84 Boundary cells of testis, 67 Bowman's capsule, 35, 36 Brain, 50-57 blood supply, 8 Branchial arches, 48, 49, 75, 78, 79, 81 Branchial arteries, 5 Branchial muscles, 48 Branchiocranium, 75, 78, 79, 81 Branchiostegal membrane, 71 Branchiostegal rays, 48, 71, 76, 78, 80 Brockman bodies, see Pancreas Brown bullhead, see Ictalurus nebulosus Brush border, see Striated border Buccal cavity, see Oral cavity Bulbus arteriosus, 5, 11, 12, 19 Capillaries, 5, 10, 34, 36 Carassius auratus, 15, 16, 54 Cardiac muscle, 11, 12, 43 Carotid artery, 5-7 Carotid sinus, 7, 8 Cartilage, histology, 48, 83, 84 Caudal artery, 5, 6, 8, 79 Caudal fin, 4, 41, 83, 84 muscles, 46 Caudal neurosecretory system, 33, 34 Caudal pars distalis, 31-33 Caudal vein, 5, 6, 8, 9, 15 Cell membrane, 26, 38 Central veins, 9, 25, 26 Centrum, 79, 83, 84 Cephalic lateral line, 4, 64, 75 Cephalic veins, 9 Ceratobranchial, 48, 49, 79, 81 Ceratohyal, 47, 48, 78, 80, 81 Cerebellum, 50, 52, 53, 55, 56 Cerebrospinal fluid, 53, 54 Cerebrum, see Telencephalon Chemoreceptors, 60, 61 Chloride cells, 71-73 Chondrocytes, 84, 85 Chondroid, 84 Chorion, see Zona radiata Choroid, 59, 60 Choroid gland, 59 Chromaffin tissue, 29, 30 Chromatophore, see Melanophore Cilia, 36, 37, 52, 61-63 Circulatory system 5-18 Circulus cephalicus, 8 Clarias batrachus, 30, 34 Clarias lazera, 54 Claustrum, 63, 82 Cleithropharyngeus profundus, 49 Cleithropharyngeus superficialis, 49 Cleithrum, 46, 49, 76, 80, 83 Club cells, see Alarm substance cells Coeliac artery, see Mesenteric artery Coeliacomesenteric artery, 6-8 Collagenous fibers, 10, 28, 85 Collecting ducts, kidney, 36, 37 Common bile duct, 23, 25-27 Common cardinal vein, 6, 9, 11 Complex vertebrae, 76, 77, 80, 82 Cones of retina, 59, 60 Convoluted tubule, see Renal tubule Coraco-branchialis, see 91 Cleithropharyngeus Coracoid, 46, 80, 83 Corium, see Dermis Cornea, 59 Coronary artrey, 7 Coronet cells, 55 Corpora atretica, 70 Corpora lutea, 70 Corpus cerebelli, 51, 53, 56 Corpuscles of Stannius, 30, 35 Corydoras aneus, 54 Counter current exchange, 73 Cranial nerves, 46, 50, 57-59 Cristae, 63 Crown cell, see Coronet cell Cucullaris, 46 Cupula, 63, 64 Cyprinus carpio, 49 Cystic artery, 8 Cystic duct, 26 Dahlgren cells, see Caudal neurosecretory system D-cells of pancreas, 30, 31 Deep dorsal flexor, 46 Deep ventral flexor, 46 Dentary, 47, 76-78, 80, 81 teeth, 19 Depressor muscles of anal fin, 45 Depressor muscles of dorsal fin, 45 Dermal bone, 83 Dermis, 15, 40-42, 54, 61, 62, 64 Desmosome, 26 Diencephalon, 31, 52-54 Digestive system, 19-27 blood supply, 6 Dilator operculi, 47 Distal segment of renal tubule, 37 Dorsal aorta, 5-8, 82, 84 histology, 9, 10 Dorsal fin, 3, 41, 76, 77, 82 muscles, 45, 46 Dorsal spine, 3, 41, 42, 45, 74, 76, 77, 82 Duct of Cuvier, see Common cardinal vein Ear, 58, 62, 63, 82 Ectethmoid, see Parethmoid Ectopterygoid, 78 Efferent arteriole of gill filament, 71. 72 Efferent branchial arteries, 5, 7 Eggs, see Oocyte Elastic arteries, 9, 10 Elastic connective tissue, 9, 12 Elastic membranes, arteries, 10 Electron microscopy techniques, 2 Encephalic arteries, 8 Endocardium, 11, 12 Endocrine pancreas, see Pancreatic islets Endocrine system, 29-34, 67, 70 Endolymph of ear, 62 Endoplasmic reticulum, 73 Endothelium, 9-11, 13, 36 Eosinophils, 17 Epaxil muscles, 45 Ependymal cells, 52-54, 56, 57 Epibranchial, 48, 49, 79, 81 Epicardium, 11, 12 Epidermis, 20, 39-42, 54, 61, 62, 64, 65 Epihyal, 76, 78, 80, 81 Epiotic, 75, 78 Epiphysis, see Pineal organ Epipleural ribs, 79 Epithalamus, 52 Epithelium, lymphocytes, 17, 22, 23 pseudostratified columnar, 37-39, 54 simple columnar, 22-27, 36, 37, 39, 67 simple cuboidal, 26, 33, 36, 39 INDEX simple squamous, 9, 13, 20, 28, 33, 54, 64, 67, 68 stratified squamous, 21, 40, 41, 64, 71 Epural, 74, 83 Erector muscles of anal fin, 45 Erector muscles of dorsal fin, 45 Erythroblast, 15, 16 Erythrocyte, 13, 15, 16, 36, 72 destruction, 14 Esophagus, 19-21, 62 blood supply, 11 connection to swim bladder, 27 Estrogen, 70 Ethmoid cartilage, 75 Excretory system, 35-39 Exoccipital, 75, 78 External anatomy, 3, 4 External carotid artery, 7 Eye, 59, 60, 75 blood supply, 7 muscles, 47, 58 Facial lobe, 56, 57 Facial nerve, 47, 58 Filum terminale, 57 Fins, 3, 41, 45, 46, 82, 83 histology; 41 Fin rays, see Lepidotrichia Follicle, ovarian, 68-70 Follicular cells, 69, 70 Fontanelles, 75 Food habits, 19 Foramen magnum, 75 Frontal, 47, 75-77 Fundic stomach, 21-23 Gall bladder, 19, 25-27 blood supply, 8 Ganglion cells, retina, 58, 60 Gas bladder, see Swim bladder Gastric artery, 8 Gastric glands, 21-23 Gastric pits, 22, 23 Gastric veins, 9 Genital artery, 8 Genital pore, 66, 68 Genital veins, 9 Germinal center, splenic corpuscles, 14 Germinal epithelium, 69 Gill, 11, 15, 35, 71-73, 79 arch, 5, 19, 48, 49, 61, 71 filaments, 5, 71, 72, 79, 84 lamellae, 5, 10, 13, 71-73 rakers, 71, 79, 81 slits, 19, 71 Gill-filament cartilage, 71, 72, 84, 85 Gillichthys, 34, 67 Glomerulus, 35, 36 Glossopharyngeal nerve, 48, 51, 59 Goblet cell, 19-27, 39-41, 61, 65, 71, 72 Goldfish, see Carassius auratus Golgi complex, 26 Gonadotrops, 33 Gonads, 19, 29, 66-70 blood supply, 6 Granulocytes, 16, 17 Granulosa cells, see Follicular cells Gray matter, 57 Growth hormone cells, see Somatotrops Gustatory receptors, see Taste bud Gut, see Digestive system Hard ray, 3, 41, see also Dorsal spine and Pectoral spine Head kidney, 19, 29, 30, 35, 62 blood supply, 6, 8, 9 hemopoiesis, 13 Head kidney artery, 8 Heart, 10-13 Hemal arch, 8, 79 Hemal spine, 44, 74, 79, 82 Hematocrit, 17, 18 Hematopoietic tissue, see Hemopoietic tissue Hemoblasts, 13-16 Hemopoiesis, 13, 15 Hemopoietic tissue, 13, 16, 29, 30, 35, 36, 83 Hemosiderin, 14 Hepatic artery, 8, 26 Hepatic bile duct, 27 Hepatic portal system, 5, 9 Hepatic portal vein, 6, 9, 13, 14, 25, 26, 30 Hepatic sinusoids, 9 Hepatic vein, 5, 6, 9, 11, 26 Hepatocytes, 25 Heterophils, see Neutrophils Histological methods, 2 Horizontal cells, retina, 60 HIorizontal septum, 45 Hormones, 29 Hyaline cartilage, 74, 83, 84 Hyohyoideus, 48 Hyoid arch, 75 Hyoid muscles, 47, 48 Hyomandibular, 47, 48, 76-78, 81 Hyopectoralis, see Rectus cervicis Hypaxial muscle, 45 Hypobranchial bone, 79, 81 Hypobranchial muscles, 49 Hypochordal longitudinal muscle, 46 Hypodermis, 40, 41 Hypogastric artery, see Urinary artery Hypohyal, 48, 49, 78, 80, 81 Hypothalanms, 52, 58 Hypurals, 74, 83, 84 Ictalurus catus, 30, 31 Ictalurus melas, 58, 65 Ictalurus natalis, 38, 61 Ictalurus nebulosus, 2, 5, 15, 24, 30, 43, 46, 61, 65, 74, 75 Iliac artery, 8 Iliac vein, 9 Inclinator muscle of anal fin, 45 Inclinator muscle of dorsal fin, 45 Inferior jugular vein, 9 Inferior lobe, 51-53, 55 Inferior oblique muscle, 47, 58 Inferior rectus muscle, 47, 50, 58 Infracarinale muscle, 45, 46 Inner ear, see Ear Insulin, 31 Integumentary system, 40-42 Interauricular granular band, 56 Intercalarium, 63, 82 Intercostal veins, 9 Interhyal, 78, 81 Interhyoideus, 48, 49 Intermandibularis anterior muscle, 47 Intermandibularis posterior muscle, 47, 48, 84 Intermediate segment of renal tubule, 37 Intermuscular bones, 79 Internal carotid artery, 7 Interopercular, 76, 79, 81 Interossicular ligaments, Weberian apparatus, 63, 82 Interradial muscles, 46 Interrenal tissue, 29 Interstitial cells, testes, 67 Intestinal arteries, 8 Intestinal sphicter, 23-25 Intestinal veins, 9 Intestine, 19-26 92 blood supply, 8 Iris, 59 Islet of Langerhan, see Pancreatic islets Jugal, 75 Kidney, 35, see also Head kidney and Trunk kidney duct, see Opisthonephric duct Kinocilium, 63 Labyrinth, ear, 62, 63 Lacrymal, 75-77 Lagena, 62, 63 Lamellae, gill, see Gill lamellae Lamina propria, 19-24 Lapillus, 64 Large pit organs, see Superficial neuromast Lateral accessory nerve, 51, 62 Lateral cutaneous area, 28, 82 Lateral line, 4, 40, 41, 45, 58, 59, 64, 65 canal, 40, 61, 64 nerve, 45, 64 pores, 4, 64 sense organs, see Neuromasts Latex injection, 5 Lens, 59 Lepidotrichia, 3, 40, 41, 45, 74, 82, 83 Leukocytes, 15-17 Levator arcus palatini, 47 Levatores arcuum branchialia, 48 Levator operculi, 47 Leydig cells, see Interstitial cells Ligamentum scaphium, 63 Ligamentum tripus, 63 Lipid droplets, 38 Liver, 19, 25-27 blood supply, 6, 8, 9, 11, 25 distribution of pancreas, 9, 25, 26 sinusoids, 10 Locking ray, dorsal fin, 45, 76, 77, 82 Lower pharyngeal bone, 20, 49, 79, 81 Lymphatic system, 13 Lymph heart, 13 Lymphocytes, 14, 16, 17, 22, 23 Macrophages, 13, 14, 17 Maculae, 63, 64 Mandibular muscles, 47 Mandibulary barbel, 3, 7, 47 Mauthner cells of spinal cord, 63 Maxilla, 47, 74, 76-78, 80 Maxillary barbel, 3, 7, 47, 48, 74, 78 Meckel's cartilage, 78 Median dorsal septum, 44 Median hypobranchial artery, 7 Median infracarinales, 45, 46 Median ventral septum, 44 Medulla oblongata, 51, 57, 62 Melanin, 11, 12, 60 Melanophores, 30, 40, 41, 57, 65 Membranous labyrinth, see Labyrinth, ear Meninx primitiva, 52-54, 56, 57, 63 Mental barbels, 3, 7, 47 Mesencephalon, 53, 55, 59 Mesenteric artery, 8 Mesentery, 24, 30, 68 Mesethmoid, 75-78 Meso-adenohypophysis, see Caudal pars distalis Mesonephric duct, see Opisthonephric duct Mesothelium, 11, 13, 20-23, 27, 28, 39, 67, 68 Meta-adenohypophysis, see Pars intermedia INDEX Metapterygoid, see Pterygoid Metencephalon, 56 Microvilli, 24, 26 Microtubules, 38 Midbrain, see Mesencephalon Middle intestine, 19, 22, 23 blood supply, 8 Mitochondria, 26, 38, 73 Monocytes, 16 Mouth, 3 Mucosa, 20 common bile duct, 26 esophagus, 20, 21 gall bladder, 26 intestine, 21, 23, 24 pancreatic ducts, 25 pneumatic duct, 27, 28 stomach, 21-23 Mucous cells, see Goblet cells Muscle, dissection technique, 43, 44 Muscular artery, 10 Muscularis, 20, 21 esophagus, 20, 21 gall bladder, 26 intestine, 21, 23, 24 pneumatic duct, 27, 28 stomach, 21-23 Muscularis mucosae, 20-24 Muscular system, 43-49 Muscular tissue classification, 43 Musculus lateralis profundus, see White muscle Musculus lateralis superficialis, see Red muscle Myelencephalon, 57 Myocommata, 44, 45, 49 Myofibril, 43 Myomeres, 44, 45 blood supply, 9 Myosepta, see Myocommata Myotome, see Myomere Nares, 3, 61 Nasal barbels, 3 Nasal bone, 75-77 Neck segment of renal tubule, 36-38 Nephron, 35 Nervous system, 50-65 Neural arch, 57, 79 Neural spine, 44, 74, 79, 82 Neurocranium, 48, 74, 78 Neurohypophysis, 31, 33, 53 Neuromast, 40, 63, 64 Neutrophils, 16, 17 Notochord, 79, 83, 84 Nuchal shield, 82 Nuclear shadows, 15 Nuclei of brain, 50 Obliqui dorsales, 49 Obliqui ventrales, 49 Oculomotor nerve, 51, 58 Oesophagus, see Esophagus Olfactory bulb, 50, 52, 58, 60 Olfactory epithelium, 60, 61 Olfactory lobe, 50-54, 59 Olfactory nerve, 58, 60 Olfactory organ, 50, 60, 61, 75 Olfactory sac, 50, 52, 58, 61 Olfactory tract, 50-52, 57 Oocytes, 67-70 Oogenesis, 68, 69 Oogonia, 68, 69 Opercular bone, 47, 76, 77, 79, 81, 84 Opercular cavity, 19, 71 Operculum, 40, 71 Opisthonephric duct, 36-89 Opisthotic, 74 Optic chiasma, 51, 52, 58 Optic lobe, 50, 51, 53, 55 Optic nerve, 7, 50, 52, 55, 58, 59 Optic tectum, 52, 53, 55, 56, 58 Oral cavity, 19 Oral valve, 71 Orbitosphenoid, 48, 75, 76 Osmoregulation, 35, 71 Osteoblasts, 83 Osteoclast, 83 Osteocyte, 83, 84 Otolith, 62, 63 Otolith organs, 62-64 Ovary, 67-70 blood supply, 8 Oviduct, 68 Ovigerous lamellae, 68 Palatine, 48, 76, 78 Palatoquadrate cartilage, 75 Pancreas, 19, 24, 25, 30, 31 endocrine, see Pancreatic islets Pancreatic ducts, 23, 25 Pancreatic islets, 24, 25, 30, 31 Parasphenoid, 48, 75, 78 Parethmoid, 47, 75-78 Parhypural, 74, 83 Parietal bone, 74 Parietal peritoneum, 28, 29, 66, 68 Pars distalis, 31, 32 Pars inferior of ear, 58, 62, 63 Pars intermedia, 31, 33 Pars nervosa, 31 Pars superior of ear, 58, 62, 63 Pectoral fins, 3, 35, 41, 42, 83 blood supply, 8 muscles, 46 Pectoral girdle, 6, 8, 48, 75, 77, 80, 83 Pectoral spine, 3, 41, 42, 46, 74, 78, 80, 83 Pelvic fins, 3, 41, 83 blood supply, 8 muscles, 46 Pelvic girdle, 46 Pericardial sac, 11, 12, 34, 49 blood supply, 7 Perichondrium, 84 Perilymph, 62, 63 Peritoneum, see Parietal peritoneum and Visceral peritoneum Pharyngeal teeth, 19, 20, 48, 49, 75, 79 Pharyngobranchials, 48, 49, 79, 81 Pharyngo-clavicularis, see Cleithropharyngeus Pharynx, 5, 19, 20, 48, 49, 71 Phoxinus, 61 Physostomous, 27 Pigment cells of retina, 60 Pilaster cells, see Pillar cells Pillar cells, 72 Pineal organ, 29, 52-54 Pituitary, 31-33, 51-53 Plasma membrane of oocyte, 68, 69 Pleural ribs, 79 Pneumatic artery, 8 Pneumatic duct, 21, 27, 28 Pneumatic vein, 9 Poison gland, see Axillary gland Postcleithrum, 83 Posterior cardinal vein, 5, 6, 9, 29, 30, 35 Posterior infracarinales, 45 Posterior rectus muscle, 47, 50, 58 Posttemporal, 46, 75-78, 80, 83 Prefrontals, 75 Premaxilla, teeth, 19, 78, 80 Preopercular, 75-79, 81 Principal islets of pancreas, 30 Pro-adenohypophysis, see Rostral pars 93 distalis Prolactin cells, 31, 32 Prootic, 48, 75, 78 Protractor ischii, see Infracarinales Proximal pars distalis, see Caudal pars distalis Proximal segment of renal tubule, 36-38 Pseudobranch, 7, 71 Pseudocartilage, 47, 61, 84 Pseudostratified columnar epithelium, 37-39, 54 Pterotic, 46-48, 75-78 Pterygoid, 47, 48, 76-78, 81 Pterygiophore, 45, 74, 76, 79, 82 Pulp cavity, teeth, 20 Purkinje cells, 56 Pylodictis, 75 Pyloric ceca, 22 Pyloric intestine, 19, 22, 23, 25, 26 blood supply, 8 Pyloric stomach, 21-23 Pyloric sphincter, 21-23 Quadrate, 76-78, 81 Radials, 80, 83 Radix, dorsal aorta, 7, 8 Rectal intestine, 19, 23, 24 blood supply, 8, 23 Rectus cervicis, 49 Red blood cells, see Erythrocytes Red muscle, 45 Red pulp, spleen, 13, 14 Renal arteries, 6, 8 Renal capsule, see Bowman's capsule Renal corpuscle, 35, 36 Renal portal capillaries, 9 Renal portal system, 9 Renal portal veins, 9 Renal tubules, 29, 35-38 Reproductive system, 66-70 Respiratory system, 71-73 Rete mirabile, 10 Reticular fibers, 14, 26 Reticulocytes, 15 Retina, 58-60 Retractor ischii, see Infracarinale Retractor lentis, 59 Retractor tentaculi, 47 Ribs, 74, 76, 77, 79, 83 Rita rita, 47 Rods of retina, 59, 60 Rostral pars distalis, 31, 32 Sacculus, 62, 63 Saccus vasculosus, 31, 51-53, 55 Sagitta, 64 Scale bone, see Supratemporal Scales, 40 Scaphium, 63, 82 Scapula, 83 Schreckstoff cells, see Alarm substance cells Sclera, 59 Segmental arteries, 8 Segmental veins, 9 Semicircular canals, 62 Seminal vesicle, 67 Seminiferous tubules, 66, 67 Serosa, 20 common bile duct, 26 esophagus, 20, 21 intestine, 13, 23, 24 opisthonephric duct, 38 pancreatic ducts, 25 pneumatic duct, 28 stomach, 22, 23 urinary bladder, 39 INDEX Sertoli cells, 66, 67 Sexual differences, 4 Silurus, 13 Simple columnar epithelium, 22-27, 36, 37, 39, 67 Simple cuboidal epithelium, 26, 33, 36, 39 Simple squamous epithelium, 9, 13, 20, 28, 33, 54, 64, 67, 68 Sinus endolymphaticus, 62, 63 Sinus impar, 62, 63, 82 Sinusoid, 10, 14, 25, 26, 72 Sinus venosus, 9, 11, 12 Skeletal muscle, esophagus, 20, 21 gross anatomy, 44-49 histology, 43 pneumatic duct, 28 Skeletal system, 74-85 methods, 74 Skin, 40-42, 45, 61, 62, 65 Skull, 74-81 Small intestine, see Intestine Small pit organ, 47, 61, 64, 65 Smooth muscle, 9, 10, 12, 21-23, 26, 27, 37-39, 67, 68 histology, 43 Soft rays, see Lepidotrichia Somatotrops, 32 Spermatids, 66 Spermatocytes, 66 Spermatogenesis, 66 Spermatogonia, 66 Spermatozoa, 66 Sphenotic, 47, 48, 75-78 Spinal cord, 33, 50-52, 57, 63, 79, 84 Spinal nerves, 49, 50, 57 Spine, see Hard ray Spleen, 13, 14, 24, 25, 27 blood supply, 6 hemopoiesis, 13 sinusoids, 10 Splenic artery, 8 Splenic corpuscle, 13, 14 Splenic vein, 9 Stannius corpuscles, see Corpuscles of Stannius Stereocilia, 63 Stomach, 19-23, 27 blood supply, 8 Stratified squamous epithelium, 21, 40, 41, 64, 71 Stratum germinativum, 40, 41, 65 Striated border, 23, 36, 37 Striated muscles, see Skeletal muscles Subarcualis rectus communis, 48, 49 Subclavian artery, 6-8 Subcutis, see Hypodermis Submucosa, 20 esophagus, 20, 21 gall bladder, 26 intestine, 23, 24 oral cavity, 19 pharynx, 19, 20 pneumnatic duct, 27, 28 stomach, 22, 23 Submucosal muscle, 21 Subopercular, 74 Suborbitals, 75-77 Subtemporal, 75-77 Superficial flexor, 46. Superficial neuromasts, 64, 65 Superior oblique muscle, 47, 50, 58 Superior rectus muscle, 47, 50, 58 Supracarinales, 45 Supracleithrum, 83 Supraethmoid, see Mesethmoid Supraoccipital, 75-78, 82 Suprarenal tissue, see Chromaffin tissue Supratemporal, 75-77 Suspensory ligament, eye, 59 Swim bladder, 19, 27, 28, 35, 62, 63, 68, 82 blood supply, 8, 10, 11 Symplectic, 74 Tapetum lucidum, 60 Taste buds, 19, 20, 21, 40, 58-62, 65 Tectum, see Optic tectum Teeth, 19, 20, 71 Tegmentum, 55 Tela choroidea, 52-54, 56 Tela submucosa, see Submucosa Telencephalon, 52, 53 Terminal cranial nerve, 58 Testis, 66, 67 blood supply, 8 Thalamus, 52 Theca, 69 Thrombocyte, 14-17 Thymus, 14, 15, 29 hemopoiesis, 13' Thyroid, 9, 10, 15, 33 blood supply, 7 Thyrotrops, 32 Tight junction of epithelial cells, 26 Transverse processes of vertebrae, 79 Transverse septum, 9, 11, 26, 33, 34 Transversi dorsales muscles, 48, 49 Transversi ventrales muscles, 49 Trigeminal nerve, 47, 58 Trigeminofacial complex, 51, 58 Tripus, 27, 63, 76, 80, 82 Trochlear, 51, 58 Trout, 1 Trunk kidney, 5, 13, 19, 30, 35, 39 blood supply, 6, 8, 9 hemopoiesis, 13 Trunk musculature, see Myomeres Tunica adventitia, 9, 10 Tunica albuginea, 66-68 Tunica externa, swim bladder, 28 Tunica interna, swim bladder, 28 Tunica intima, 9, 10 Tunica media, 9, 10 Tunica mucosa, see Mucosa Tunica muscularis externa, see Muscularis Tunica propria, see Lamina propria Tunica serosa, see Serosa Ultimobranchial gland, 33, 34 Upper pharyngeal bone, 20, 48, 49, 79, 81 Urinary artery, 8 Urinary bladder, 19, 35, 38, 39, 43 blood supply, 8 Urogenital opening, 3, 4, 38 Urogenital papilla, 4 Urohyal, 49, 79, 80 Uroneural, 57, 74, 83 Urophysis, 34 Utriculus, 62, 63 Vacuoles, 42 Vagal lobe, 51, 57, 59 Vagus nerve, 48, 51, 59 Valves, heart, 12 Valvula cerebelli, 53, 56 Veins, gross anatomy, 5, 6, 9 histology, 8, 10, 11, 24 Ventral aorta, 5, 6, 10, 12 histology, 9 Ventricle, 11, 12, 19, 52, 54, 57 Ventriculus communis, 52-54 Venules, 9 Vertebrae, 7, 8, 10, 74, 76, 77, 79, 82-84 Visceral peritoneum, 20, 68 Vitelline membrane, 68 Vomer, 75, 78 Weberian apparatus, 63, 79, 82 Weberian ossicles, 62, 63, 82 connection to swim bladder, 28 White blood cells, see Leukocytes White catfish, see Ictalurus catus White matter, 57, 63 White muscle, 45 White pulp, spleen, 13, 14 Wolffian duct, see Opisthonephric duct Yolk, 69 Zona pellucida, see Zona radiata Zona radiata, 68, 69 Zygopophyses, 79 Zymogen, 24 94 a <~a a -s -~ a -~ -a -a-a K -A -a 5- A a ~K5 a -~ K --A. K- a-ag- K K a A -5 ~ -- a-- K #>~Kaa~ KK-- ~ 55K -' - K-K K- 4 5 5 -K ~-K~K-55-sK-- A. ASKKa-K -a A K~K- K- 5 K K- K K K ~ /a~4AA~AaW7 K->K-K,~-a~ -s~ 5 4 K, - ~ SK~K, K a ~ --K -- K- - K~ a-a-A~ss -- KK~a ~ ~-K, ~ --- K---- - - ~-~-a-~K- 5 KKKKKK- -sAK, -s-- K~K--~- K5K~K-KKKK 55 KsKK-A ~ -~ -~K5s-K. - a -s-K---KAaaAg. 55KK5<. ~K~KKK'KKK K K- a~K K, 5 ss~AK ~sK~ -a---K5K-<~~ ~ >~sAK5i~KsK j~sK> K- 77 77 a K- ,~K<K-KK-a~KKK-K ~ K-K 5 A~ AK.K~~K'5KK-K.K.(K- A ~ ~K-K~sA>~KAKKKK.~sK.A K 'K5 ~VKAK4~K-~K.K- KKSKK.A KAy-s- ~ - ( ~AKK.~K- 5KASk/SK.AA~K.KSK. Aa 2~AA~~AKK-KKK- ~K~K- a ~ K-- --AKS a-- KKK-KK~~~K-~ ~ K - a K-~KK- --A--- K- - -- ~K ~->~~~/$> K-K-K 4 K-K---K--1-~~SK-s:~; K-a K- K-KSsK-K--K-K- K-~-K-K-K- K-Pm SaAK-sA 4A-<~Ai K-AK-KK-K-KK- { aA~ K--~K~K AK 55 K.K- 5' - K-< >jK-SKK-K~> KaK----K- -~5-K-a-K~ K--A-s. - AK-/AK- ~s~KK-< sAK- '~ - - ~ K- ss(aK . K- K- ~ - - K,~ K. K K-K-AK-,- - -5 5 K- K-KAK- K-K- -a-- ~ -ssK-> K-K-K-KKK-KK- 5 A -- K-a- K- K KK. AK-AK, K-a K-KK.~AK-K- ---- %~/~AKsAK-K-K,>s55a ~/~KK-KK-KK- A-/--<- K- - AK- - K ~. -K-K-K- 55K-K-K-K- 5K-A/aK-K- KK-KK-a~- -aK/ 5 5~ K- A - K-K--K- >K, a-K-K.Ay~K,~p K--~K-K--~KaA~K------K-KK-~ KK- K- aK-a.A-'a~ 5K-K- aVK->K->-K-K-. K-K s~A ~ --- A-AK, K-K K-~ - ---- k--a- ~K-5'K-KAKK-aK- - --- K-- -A-s AK- a K-KKK-- - - K-K-KaK- K a -a K-~ K - - - - AK--AyK-K- ~K-~K-~K-f{ ~AK-KKK-K-a KA- - K--a K K-K AKK-KA -A K.K-4AAAaK-K-K-K-K- ~ K-K-K-A K-AK-AK- ~. A -- 7AK-K-77K.K-K-AKKAK5K. K-5S5KKAK-K-A{K-4KK- ~KKK-JK-4K-~~K-KKKK'aK K- a- K-K- K.-]YA~ <~y~K-~K-4777- -- KK-A