Research and Development Series No. 22
Project: AID/DSAN-G 0039
April 1979
WATER QUALITY
MANAGEMENT
IN POND FISH
CULTURE
International Center for Aquaculture
Agricultural Experiment Station
R. Dennis Rouse, Director
Auburn University
Auburn, Alabama
CO0N TE NT S
Page
RELATIONSHIPS BETWEEN WATER QUALITY AND FISH PRODUCTION--...3
Temperature -------------------------------------------------------------------- 3
Salinity --------------------------------------------------------------------------- 4
Turbidity and Color ---------------------------------------------------------- 4
Plankton-------------------------------------------------------------------------- 5
Dissolved Oxygen ------------------------------------------------------------- 7
pH -------------------------------------------------------------------------------- 9
Carbon Dioxide---------------------------------------------------------------- 10
Ammonia ------------------------------------------------------------------------ 10
Hydrogen Sulfide-------------------------------------------------------------- 11
Total Alkalinity and Total Hardness-------------------------------------- 11
Aquatic Weeds----------------------------------------------------------------- 11
Pollutants ------------------------------------------------------------------------ 11
WATER QUALITY MANAGEMENT-------------------------------------------------- 11
Inorganic Fertilizers---------------------------------------------------------- 11
Organic Fertilizers------------------------------------------------------------- 14
Liming----------------------------------- ---------------------------------------- 14
Removal of Clay Turbidity ------------------------------------------------- 16
Reduction of pH -------------------------------------------------------------- 16
Dissolved Oxygen------------------------------------------------------------- 17
Fish Feeding and Water Quality ------------------------------------------ 18
Aquatic Plant Control--------------------------------------------------------- 19
Calculations for Chemical Treatment----------------------...............19
WATER ANALYSIS --------------------------------------------------------------------- 20
Sampling Water---------------------------------------------------------------- 20
Water Analysis Kits------------------------------------........................21
Secchi Disk Visibility -------------------------------------------------------- 22
BIBLIOGRAPHY ------------------------------------------------------------------------ 25
GLOSSARY ----------------------------------------------------------------------------- 27
METRIC AND ENGLISH EQUIVALENTS-------------------------------------------- 30
CELSIUS To FARENHEIT DEGREES ----------------------------------------------- 30
CHEMICAL SYMBOLS OF SELECTED ELEMENTS-------------------------------- 30
PUBLISHED APRIL 1979-IM
SECOND PRINTING DECEMBER 1979-1IM
THIRD PRINTING AUGUST 1 980-2M
FOURTH PRINTING OCTOBER 1982-2M
Information contained herein is available to all without
regard to race, color, or national origin.
Water Quality Management in Pond Fish Culture
Claude E. Boyd and Frank Lichtkoppler*
WATER QUALITY includes all physical, chemical, and
biological factors that influence the beneficial use of water.
Where fish culture is concerned, any characteristic of water that
affects the survival, reproduction, growth, production, or man-
agement of fish in any way is a water quality variable.
Obviously, there are many water quality variables in pond fish
culture. Fortunately, only a few of these normally play an
important role. These are the variables that fish culturists should
concentrate on, and attempt to control to some extent by
management techniques.
All other things being equal, a pond with "good" water quality
will produce more and healthier fish than a pond with "poor"
water quality. In this report an attempt is made to define "good"
water quality for fish culture. Information is also presented
which will help in determining the potential of a body of water
for producing fish, improving water quality, avoiding stress-
related fish disease and parasite problems, maintaining fish for
research purposes, and ultimately producing more fish per unit
of surface area. The following discussion of water quality is
brief, but an attempt has been made to cover the most important
points. The first part is concerned with general aspects of water
quality which influence fish production. Next, several important
water quality management techniques are outlined in simple
form. Finally, some suggestions are made regarding water
analysis in fish culture. Also included is a glossary which contains
definitions of the technical terms. The information in this report
is essentially a summary of the book, Water Quality in
Warmwater Fish Ponds, by Boyd (17). This book may be
consulted for more details and for additional references to the
literature on water quality in ponds.
RELATIONSHIPS BETWEEN WATER QUALITY
AND FISH PRODUCTION
The material in this report explains the usual relationships
between water quality variables and fish production, setting
forth, where possible, ranges of desirable levels of the variables.
In addition, the management procedures recommended herein
will usually be effective in improving water quality. However,
because of unexplained reasons, effects of water quality on fish
and the effectiveness of management procedures may be quite
different from those reported here. Therefore, fish culturists
should not consider the information in this report as the final
answers to water quality problems, but merely as suggestions on
how to solve these problems. Coldwater fish will not be
considered, but coldwater fish generally demand water of much
better quality than do warmwater fish.
*Professor and Research Associate, respectively, Department of
Fisheries and Allied Aquacultures.
Temperature
Warmwater fish grow best at temperatures between 250 and
32
0
C (Celsius). Water temperatures are in this range the year
around at low altitudes in the tropics, but in temperate regions
water temperatures are too low in winter for rapid growth of fish
and fish food organisms. For this reason, management
procedures such as feeding and fertilizing are halted or reduced
in winter. Temperature has a pronounced effect on chemical
and biological processes. In general, rates of chemical and
biological reactions double for every 10
0
C increase in
temperature. This means that aquatic organisms will use twice as
much dissolved oxygen at 30
0
C as at 20
0
C, and chemical
reactions will progress twice as fast at 30
0
C as at 20
0
C.
Therefore, dissolved oxygen requirements of fish are more
critical in warm water than in cooler water. Chemical treatments
of ponds also are affected by temperature. In warm water,
fertilizers dissolve faster, herbicides act quicker, rotenone
degrades faster, and the rate of oxygen consumption by
decaying manure is greater.
In ponds, heat enters at the surface so surface waters heat
faster than lower waters. Since the density of water (weight per
unit volume) decreases with increasing temperature above 4'C,
the surface waters may become so warm and light that they do
not mix with the cooler, heavier waters in lower layers. The
separation of pond waters into distinct warm and cool layers is
called thermal stratification. The upper warm layer is called the
epilimnion and the lower, cooler layer is known as the
hypolimnion. The layer of rapidly changing temperature
between the epilimnion and the hypolimnion is termed the
thermocline. The temperature profile for a thermally stratified
pond is shown in figure 1. In temperate regions large ponds may
stratify in the spring and remain stratified until fall. In small,
shallow ponds in temperate regions and in tropical ponds,
stratification often exhibits a daily pattern. During the day, the
surface waters warm and form a distinct layer. At night the
surface waters cool to the same temperature as the lower waters
and the two layers mix. An extensive discussion on thermal
stratification may be found in any standard text on limnology.
In some ponds, the surface waters may reach temperatures of
35
0
C or more. This is above the optimum temperature for most
warmwater fish, but the fish may seek haven from the high
temperature in subsurface waters. Fish have poor tolerance to
sudden changes in temperature. Therefore, one should not
remove fish from water of one temperature and suddenly thrust
them into a water of appreciably higher or lower temperature.
Often, a sudden change in temperature of as little as 5
0
C will
stress or even kill fish. The effect is usually worse when moving
fish from cooler to warmer water. Since temperatures increase
with decreasing altitude, one must allow for temperature
Depth,
meters
0-
0.5 epilimnion
1.0-
1.5- thermocline
2.0-
20 22 24 26 28 30 
32
Temperature, 
0
C
FIG. 1. A well developed pattern of thermal stratification In a fish
pond. The epilimnion, thermocline, and hypolimnion are Indicated.
adjustment when moving fish from high altitude to low altitude
waters. Fish readily tolerate gradual changes in temperature.
For example, one could raise the temperature from 25
0
C to 32'C
over several hours without harming fish, but fish suddenly
removed from 25
0
C- water and placed in water of 32'C might
die.
Salinity
The term salinity ref ers to the total concentration of all
dissolved ions in a natural water expressed in milligrams per liter
or parts per million'. The osmotic pressure of water increases
with increasing salinity. Fish species diff er in their osmotic
pressure requirements, so the optimum salinity for fish culture
differs to some extent with species. Salinity information on some
cultured species of pond fish is presented in table 1.
Fish are highly sensitive to sudden changes in salinity. Fish
living in water at one concentration of salinity should 
not
suddenly be placed in water with a much higher or lower
salinity. Small fish and fry of most species are more susceptible
than adult fish to sudden changes in salinity. Sodium chloride
may be used to increase the salinity in fish holding facilities and
even in small experimental ponds. Conversely, salinity may be
lowered in small scale systems by the addition of water with low
salinity. Unfortunately, it is usually not practical to -adjust the
salinity of larger fish culture systems, except in brackishwater
'One part per million (p.p.m.) indicates that there is 1 part by weight
of a substance in 1 million parts of the solution. A water sample witthi
ppm. salinity would contain 1 milligram of ions and 999,999 milligrams
of water. For all practical purposes, 1 ppm. equals 1 milligram per liter.
TABLE 1. HIGHEST CONCENTRATIONS OF SALINITY WHICH PERMIT
NORMAL SURVIVAL AND GROWTH OF SOME CULTURED 
FOOD FISH
Species Salinity, Rernc
mg/liter eeec
Catla catla (catla) .............. slightly brackish water (37)
Labeo rohita (roha) ............. slightly brackish water (37)
Ctenopharyngodon idella
(grass carp).................... 12,00 (39)
Cyprinus carpio (common carp) 9)000 (21)
Hypophthalmichthys molitrix
(silver carp).................... 8,000 (39)
Ictalurus punctatus
(channel catfish)................ 11,000 (48)
Tilapia aurea...................... 18,900 (21)
T. nilotica........................ 24,000 (21)
T. mossambica.................... 30,000 (21)
Mugil cephalus (grey mullet) ... 14,5500 (21, 26)
Chanos chanos (milkfish) ..... 32,000 (6)
of a water is to measure the total dissolved solids concentration.
A sample is filtered through a fine paper, a known volume is
evaporated, and the residue remaining is weighed. The weight
of the residue in milligrams per liter is the total dissolved solids
concentration, and this closely approximates the salinity. In
brackishwater, salinity may be estimated from the chloride
concentration by the following equation from Swingle (65):
Salinity in mg/liter = 30 + (1.805) (chloride in mg/liter)
In practice, chloride concentration (chlorinity) can be mea-
sured by ref ractometers or temperature corrected h ydrometers.
The degree of salinity in water reflects geological and
hydrological conditions. Surface waters in areas of high rainfall
where soils are continually leached usually have low salinity (10
to 250 milligrams per liter). In arid regions, evaporation exceeds
precipitation and salinity increases as a result of evaporation.
Salinity values in ponds of arid regions often range between 500
and 2,500 milligrams per liter, and much higher values are often
encountered. Even in areas of high rainfall, ground water from
wells may sometimes have salinity values as high as those
encountered in surf ace waters of arid regions. Seawater has a
high salinity (35,000 milligrams per liter) , so the salinity of
brackishwater ponds reflects the degree of dilution of seawater
with freshwater. High rates of evaporation in brackishwater
ponds during periods of low rainfall may cause them to become
excessively saline. Salinities in excess of 45,000 milligrams per
liter are difficult for even marine species to tolerate.
Turbidity and Color
The term turbid indicates that a water contains suspended
material which interferes with the passage of light. In fish ponds,
turbidity which results from planktonic organisms is a desirable
trait, whereas that caused by suspended clay particles is
undesirable. Even with the latter condition, the clay particles are
seldom abundant enougah in water to directly harm fish. If the
humates are typically quite acid and have a low total alkalinity.
Phytoplankton
SkInsects Sunfish Bass
. Zooplonkton
oeaten by 
small fish
C Detritus
FIG. 2. A representative food web in a sunfish-bass pond.
Although color does not affect fish directly, it restricts light
penetration and reduces plant growth. Agricultural limestone
applications have been used to successfully remove humates
from natural waters (74).
Plankton
Plankton is comprised of all the microscopic organisms which
are suspended in water and includes small plants
(phytoplankton), small animals (zooplankton), and bacteria.
When there is enough plankton in the water to discolor it and
make it appear turbid, the water is said to contain a plankton
"bloom." The phytoplankton uses inorganic salts, carbon
dioxide, water, and sunlight to produce its own food. The
zooplankton feeds on living or dead plankton and other tiny
particles of organic matter in the water. Bacteria utilize any type
of dead organic matter in the water for food. In fish culture
systems where fish are not provided supplemental feed,
plankton forms the most abundant base of the food web.
Examples of food webs in fish culture systems are given in
figures 2 and 3. Both food webs begin with phytoplankton
growth. In figure 2 there are several steps before ending with
largemouth bass, while in figure 3 the food web is simpler
because the tilapia feed directly on plankton. Since each step in
the food web is rather inefficient, a fish culture system with a
more direct food web will produce a greater weight of fish per
unit area. For example, during a 6-month period, the sunfish-
bass culture might produce 200 kilograms of fish per hectare
while the tilapia culture could easily produce 1,000 kilograms.
Because plankton is at the base of the food web, there is a close
relationship between plankton abundance and fish production
(58, 66), figure 4. In addition to encouraging fish growth,
plankton makes water turbid and prevents the growth of
undesirable aquatic weeds through shading (59). Despite the
benefits of plankton blooms in fish ponds, more plankton can
sometimes be produced than can be utilized by the fish for
growth. Heavy plankton blooms usually contain large numbers
of blue-green algae which can form scums at the surface. These
scums absorb heat during the day and cause shallow thermal
stratification (8, 64). During the night, heavy plankton blooms
consume large amounts of dissolved oxygen and may cause
oxygen depletion before the next morning. Scums of plankton
may suddenly die, decompose, and cause oxygen depletion.
Relationships between plankton and dissolved oxygen will be
treated more thoroughly later. In addition to causing dissolved
oxygen problems, organisms in heavy plankton blooms often
produce substances which impart a strong off-flavor to fish flesh
(44).
There are many techniques for measuring plankton
abundance, but most are too tedious for use in practical fish
culture. The most practical technique for use in ponds which do
not contain appreciable clay turbidity is to measure the Secchi
disk visibility (2). Details for making Secchi disk measurements
will be given later, but for now it will suffice to state that the
Secchi disk visibility is the depth at which a disk 20 centimeters
in diameter with alternate black and white quadrants
disappears from view. There is a high correlation between
Secchi disk visibility and plankton abundance, as illustrated in
figure 5 with data from Almazan and Boyd (2). It is impossible to
establish an ideal plankton turbidity for fish culture. However, a
Secchi disk visibility in the 30- to 60-centimeter range is
generally adequate for good fish production and for shading
underwater weeds. As Secchi disk visibilities decrease below 30
centimeters, there is an increase in the frequency of dissolved
oxygen problems. At values above 60 centimeters, light
penetrates to greater depths encouraging underwater
macrophyte growth, and there is less plankton to serve as food
for fish or fish food organisms.
Plankton communities are constantly changing in species
composition and in total abundance. This results in
corresponding fluctuations in Secchi disk visibility and in the
appearance of pond water. These changes in plankton
communities may be disconcerting to the fish culturist.
However, unless plankton becomes so dense that dissolved
oxygen problems occur or so thin as to encourage underwater
weeds, the changes do not affect fish production appreciably.
FIG. 3. A representative food web in a pond used for tilapla culture.
Sunfish
production,
kg/ha
*
600 -
0
_ *
0
zoo- *0
0
0
0h
400 - o
o@
000
0-0
01- I I I I I I
0 5 10 15 20 25 30 35
Particulate organic matter, mg/liter
FIG. 4. Plankton production (particulate organic matter) and sunfish
production in ponds. Data from Smith and Swingle (58) and Swingle
and Smith (66).
By monitoring Secchi disk visibility on a regular schedule (once
or twice weekly) and observing the appearance of the water, the
fish culturist can obtain information on the continuing condition
of the plankton community in a pond and on the supply of fish
food organisms.
The ability of water to produce plankton depends on many
factors, but the most important is usually the availability of
inorganic nutrients for phytoplankton growth. Essential
elements for phytoplankton growth include carbon, oxygen,
hydrogen, phosphorus, nitrogen, sulfur, potassium, sodium,
calcium, magnesium, iron, manganese, copper, zinc, boron,
cobalt, chloride, and possibly others. Phosphorus is most often
the element regulating phytoplankton growth in ponds (36, 47).
The addition of phosphate fertilizer will cause an increase in
plankton production and an increase in fish production in most
ponds. Inadequate supplies of nitrogen, potassium, and carbon
also limit phytoplankton in some ponds.
In general, the level of plankton production in unmanaged
TABLE 2. WATER QUALITY IN 26 FERTILIZED PONDS, 34 UNFERTILIZED
PONDS ON WOODED WATERSHEDS, AND 53 UNFERTILIZED PONDS
IN PASTURES - DATA MODIFIED AFTER BOYD (13)
Unfertilized ponds
Fertilized
Measurement Wooded Pasture ponds
watershed watershed
Total hardness (mg/liter) ..... 18.9 29.0 20.0
Soluble inorganic phosphorus
(mg/liter) ................. .01 .02 .02
Nitrate (mg/liter).............. .33 .43 .32
Ammonia (mg/liter) .......... .. 06 .13 .12
Potassium (mg/liter) ......... 1.5 2.9 1.7
Secchi disk visibility (cm) ..... 124 66 76
Plankton (mg/liter) ........... . 5.3 11.9 12.1
Particulate
organic matter,
mg/liter
40-
30
20-
00
". "
*
_o- .*." .:?,"*..-
* @0..
0-
0 1:0 I I I I I I l I I
0 1.0 2.0 3.0
Secchi disk visibility, meters
FIG. 5. Relationship between plankton abundance (particulate
organic matter) and Secchi disk visibility in fish ponds. After
Almazan and Boyd (2).
ponds is related to the basic soil fertility of the surrounding
watersheds. Therefore, the basic levels of plankton and fish
production are greater in ponds located on watersheds with
fertile soils than in ponds located on watersheds with poor soils.
The management practices on watersheds also influence
plankton production in ponds. According to a study by Boyd
(13), unfertilized ponds in pastures had higher concentrations of
nutrients, harder water, higher plankton production, and less
transparent water than unfertilized ponds in woods, table 2. In
fact, the average plankton production in unfertilized pasture
ponds almost equalled plankton production in fertilized ponds,
table 2. Although little of the nitrogen and phosphorus applied to
pastures is lost in runoff, high concentrations of nutrients in
unfertilized pasture ponds were related to agricultural activities
on the watersheds. For example, cattle grazing on pastures
deposited considerable urine and manure in or near ponds,
which served as a source of nutrients.
Even though the basic fertility of ponds differs greatly
depending on the management and soils of their watersheds, the
level of plankton production in most ponds can be raised within
the range of plankton production needed for good fish
production. Inorganic fertilizers may be added to ponds with
low basic fertility to increase plankton production. In some
ponds, both lime and fertilizer application may be required to
increase plankton production. Manures also increase plankton
production.
,,
Dissolved Oxygen
Dissolved oxygen is probably the most critical water quality
variable in fish culture, so the fish culturist should be familar
with the dynamics of dissolved oxygen concentrations in ponds.
The atmosphere is a vast reservoir of oxygen, but atmospheric
oxygen is only slightly soluble in water. The solubility of oxygen
in water at different temperatures and at standard sea level
atmospheric pressure is given in table 3. From this table, it is
readily apparent that the solubility of oxygen in water decreases
as the temperature increases. When water contains a dissolved
oxygen concentration equal to the solubility of oxygen in water
at the existing temperature, the water is said to be saturated with
dissolved oxygen. If water contains more dissolved oxygen than
it should for the particular temperature, it is supersaturated.
Water may also contain less dissolved oxygen than the saturation
value. The solubility of dissolved oxygen decreases with
decreasing atmospheric pressure (barometric pressure). For
example, the solubility of oxygen in water at 25
0
C differs as
follows with altitude (given in milligrams per liter at specified
altitudes): 0 meters, 8.4 milligrams per liter; 500 meters, 7.9
milligrams per liter; 1,000 meters, 7.4 milligrams per liter; 1,500
meters, 7.0 milligrams per liter; 2,000 meters, 6.6 milligrams per
liter; 2,500 meters, 6.2 milligrams per liter; and 3,000 meters, 5.8
milligrams per liter. The solubility of oxygen in water also
decreases as salinity increases. At temperatures of 20 to 35
0
C, the
solubility of dissolved oxygen decreases by about 0.008
milligram per liter for each 210 milligrams per liter increase in
salinity (3).
TABLE 3. SOLUBILITY OF DISSOLVED OXYGEN IN PURE WATER AT
STANDARD SEA LEVEL ATMOSPHERIC PRESSURE
(1 ATMOSPHERE)
0
C mg/liter 
0
C mg/liter 
0
C mg/liter
0....... . 14.16 12....... . 10.43 24....... . 8.25
1....... . 13.77 13....... . 10.20 25....... . 8.11
2....... . 13.40 14....... . 9.98 26....... . 7.99
3 ....... 13.05 15....... 9.76 27....... 7.86
4 ....... 12.70 16....... 9.56 28....... 7.75
5 ....... 12.37 17....... 9.37 29 ........ 7.64
6 ....... 12.06 18 ....... . 9.18 30....... 7.53
7 ....... 11.76 19....... 9.01 31....... 7.42
8 ....... 11.47 20....... 8.84 32....... 7.32
9 ....... 11.19 21....... 8.68 33....... 7.22
10 ....... 10.92 22....... 8.53 34....... 7.13
11 ....... 10.67 23....... 8.38 35....... 7.04
Even though dissolved oxygen will diffuse into water, its rate
of diffusion is quite slow. Therefore, photosynthesis by
phytoplankton is the primary source of dissolved oxygen in a
fish culture system. Fish culturists are often concerned with the
rate at which dissolved oxygen is removed from the water. The
primary losses of dissolved oxygen from a pond include
respiration by the plankton (phytoplankton included),
respiration by fishes, respiration by benthic organisms
(organisms living in or attached to the mud), and diffusion of
oxygen into the air (20, 57). The gains and losses of dissolved
oxygen in a pond are summarized in table 4 along with some
values representing the usual magnitudes of daily gains and
losses. It is readily apparent that plankton and fish respiration
cause the major losses of dissolved oxygen and that
photosynthesis is the largest source. Diffusion of oxygen into
ponds only occurs when waters are below saturation and
diffusion of oxygen out of ponds only occurs when waters are
supersaturated. The larger the difference between the dissolved
oxygen concentration in the pond water and the concentration
of dissolved oxygen at saturation, the greater is the rate of
diffusion. Wind and wave action also favor diffusion.
TABLE 4. RANGES OF EXPECTED GAINS AND LOSSES OF DISSOLVED
OXYGEN CAUSED BY DIFFERENT PROCESSES IN FISH PONDS,
FOR PONDS OF 1.0 TO 1.5 METERS AVERAGE DEPTH
Process 
Range,
mg/liter
Gains
Photosynthesis by phytoplankton .................... 5 to 20
D iffusion ......................................... 1 to 5
Losses
Plankton respiration ................................ 5 to 15
Fish respiration .................................... 2 to 6
Respiration by organisms in mud .................... 1 to 3
Diffusion.................... .................... I1 to 5
In a fish culture system, more oxygen must enter or be
produced in the water by plankton than is used by the organisms
or dissolved oxygen depletion will occur. Since nutrients are
normally abundant in well-managed fish ponds, light is often the
primary factor regulating photosynthesis by phytoplankton.
Light rapidly decreases in intensity as it passes through water.
This is true even in pure water, but the decrease is even faster in
fish ponds because the planktonic organisms and other
suspended and dissolved substances reflect and absorb light.
Therefore, the rate of oxygen production by phytoplankton
decreases with depth, and below a certain depth, no more
oxygen is produced. Since oxygen is continually used by the
pond biota and only produced during daylight hours by the
phytoplankton, there is a depth at which dissolved oxygen
production by the phytoplankton and that entering by diffusion
just equal the combined utilization of dissolved oxygen by
pond life (32). Below this depth in stratified ponds the water will
contain no dissolved oxygen. The stratification of dissolved
oxygen in ponds usually corresponds closely to thermal
stratification (8). The epilimnion contains dissolved oxygen and
the hypolimnion is depleted of dissolved oxygen. As with
thermal stratification, daily dissolved oxygen stratification may
occur in small, shallow ponds.
Obviously, the depth to which light intensity is great enough
FIG. 6. Dissolved oxygen concentrations In the afternoon at different
depths in ponds with different densities of plankton.
so.m. Noon 6p.m. 12p.m. 6a.m.
Time of day
FIG. 7. Dally fluctuations in dissolved oxygen concentrations of
surface water in ponds with different densities of plankton.
for adequate photosynthesis to provide surplus dissolved
oxygen is related to plankton density. Photosynthesis decreases
with decreasing light intensity, and as plankton becomes more
abundant, the rate of oxygen consumption by the plankton
community increases. When plankton abundance is great,
dissolved oxygen production is extremely high near the surface.
Because of shading, the rate of oxygen production will decrease
rapidly with depth and only a thin layer of surface water, often
less than 1 meter, will contain appreciable dissolved oxygen
(32). In ponds where plankton is less abundant, rates of
dissolved oxygen production are not as high within the
illuminated layer of water, but there will be appreciable oxygen
production and surplus dissolved oxygen at greater depths than
in ponds with greater plankton turbidity. The influence of
plankton turbidity on the depth distribution of dissolved oxygen
Dissolved
oxygen,
mg/liter
Dissolved
oxygen,
mg/liter
20- r 
heavy plankton
FIG. 9. Decline in phytoplankton following a phytoplankton die-off
In a fish pond. The die-off began on April 29. After Boyd et al. (19).
in ponds is illustrated in figure 6. As a general rule, most ponds
will contain enough dissolved oxygen to support fish to a depth
of at least two or three times the Secchi disk visibility.
There is also a marked fluctuation in dissolved oxygen
concentration during a 24-hour period in ponds. Concentrations
of dissolved oxygen are lowest in the early morning just after
sunrise, increase during daylight hours to a maximum in late
afternoon, and decrease again during the night. The magnitude
of fluctuation is greatest in ponds with heavy plankton blooms
and least in ponds with low plankton abundance. Daily
fluctuations of dissolved oxygen concentrations in ponds with
different plankton densities are depicted in figure 7. In ponds
with extremely dense plankton blooms, dissolved oxygen
concentrations will often be below 2 milligrams per liter in early
morning. Concentrations are particularly low during periods of
cloudy weather (64). The production of oxygen on a cloudy day
is less than on a clear or partly cloudy day, so dissolved oxygen
concentrations do not increase to usual afternoon levels. This
results in lower than usual dissolved oxygen concentrations the
following morning. Extended periods of cloudy weather may
result in dangerously low dissolved oxygen concentrations even
in ponds with moderately heavy plankton blooms. The
influence of cloudy weather on dissolved oxygen concentrations
is illustrated in figure 8.
In ponds with heavy plankton blooms, scums of algae often
form at the surface. Occasionally, the algae in these scums will
suddenly die, and their decomposition will result in depletion of
dissolved oxygen (7,19, 64). For example, figure 9 illustrates the
Total
phytoplankton,
thousands/mi
6a.m. 6o.m. 6a.m. 6a.m
Time of day
FIG. 8. Influence of cloudy weather on dissolved oxygen
concentrations in fish ponds.
MayApril
II
FIG. 10. Concentrations of dissolved oxygen before and 
after a
phytoplankton die-off in a fish pond. The phytoplankton 
began
dying on April 29. After Boyd et al. (19).
sudden death of phytoplankton in a fish pond. 
The dissolved
oxygen concentration quickly dropped 
below a detectable
level, figure 10. Dissolved oxygen concentrations 
did not return
to normal levels until a new phytoplankton community 
was
established (examine figures 9 and 10). Phytoplankton 
die-offs
usually occur during calm, clear, warm weather. 
One can
recognize a die-off because the algal scum deteriorates 
and the
water takes on a brown or gray appearance.
Winds or heavy, cold rains may break up thermal stratification
in ponds (64), causing complete mixing ("overturn") 
of the
oxygenless waters of the hypolimnion and the 
oxygenated water
of the epilimnion. If the pond contains a large 
volume of
oxygenless water, oxygen depletion may result.
Fish require adequate concentrations of dissolved 
oxygen for
survival and growth. The minimum concentration 
for fish
survival varies with time of exposure. A fish 
may tolerate a
particularly low concentration of dissolved oxygen 
for a few
hours without ill effect, but will die if exposed 
to this same
TABLE 5. REPORTED LETHAL CONCENTRATIONS OF DISSOLVED 
OXYGEN
FOR SELECTED SPECIES OF POND FISH-DATA FROM
DOUDOROFF AND SHUMWAY (24)
Species 
Lethal level,
mg/liter
Carassius auratus (goldfish) ..... ................... 
0.1 to 2.0
Catla catla (catla).................................. 
0.7
Cirrhina mrigala (mrigal) .......................... 
0.7
Ctenopharyngodon idella (grass carp) ...............
0.2 to 0.6
Cyprinus carpio (common carp) .................... 0.2 
to 0.8
Hypophthalmichthys molitrix (silver carp) ............
0.3 to 1.1
Labeo rohita (rohu) ... ........................... 
0.7
Ictalurus punctatus (channel catfish) ................ 
0.8 to 2.0
Lepomis macrochirus (bluegill) ..................... 0.5 
to 3.1
Micropterus salmoides (largemouth bass) ............ 
0.9 to 3.1
Dissolved
oxygen,
mg/liter
12r-
The pH is a measure of the hydrogen ion concentration and
indicates whether the water is acidic or basic in reaction. The 
pH
0 small fish survive
short exposure
0.3 -
lethal if exposure
.0 prolonged
.0
5.2.0
E
S3.0 fish survive, but growth
0oslow 
for prolonged
Q) exposure
0
U)
o4.0-
5.0--
desirable range
FIG. 11. Effects of dissolved oxygen concentrations 
on pond fish.
concentration for several days. The concentration 
of dissolved
oxygen tolerated by pond fishes is illustrated in figure 11, 
with
additional data on oxygen requirements presented 
in table 5.
Low dissolved oxygen concentrations adversely affect fish 
even
at levels which do not cause mortality, making 
them more
susceptible to parasites and diseases (49). In addition, 
fish do not
feed or grow as well when dissolved oxygen concentrations
remain continuously below 4 or 5 milligrams 
per liter (4). Daily
fluctuations of dissolved oxygen in fish ponds 
apparently have
little effect on feeding and growth as long as 
the minimum
dissolved oxygen concentration for the day does 
not drop below
1 or 2 milligrams per liter in the early morning and 
then rises near
saturation within a few hours after sunrise. If dissolved 
oxygen
concentrations remain at less than 3 or 4 milligrams 
per liter for
prolonged periods, fish cease to feed or grow well.
pH
22
April
May
pH
IOr
pH
81-
I
1
I I I
6p.m.
Time of day
6a.m. Noon 12p.m. 6a.m.
FIG. 12. Daily fluctuations in pH in a fish culture pond.
scale ranges from 0 to 14, with pH 7 being the neutral point.
Thus, a water of pH 7 is neither acidic nor basic, while a water
with pH below 7 is acidic and one with a pH above 7 is basic. The
greater the departure from pH 7, the more acidic or basic a
water. The pH of natural waters is greatly influenced by the
concentration of carbon dioxide, an acidic substance.
Phytoplankton and other aquatic vegetation remove carbon
dioxide from the water during photosynthesis, so the pH of a
body of water rises during the day and decreases during the
night, figure 12. Waters with low total alkalinity often have pH
values of 6 to 7.5 before daybreak, but when phytoplankton
growth is heavy, afternoon pH values may rise to 10 or even
higher (63). Fluctuations in pH are not as great in water with
- acid death point
no reproduction
i
4-
5
6
7
8
9
slow growth
10 -
IIL
desirable range for fish
production
alkaline death point
FIG. 13. Effect of pH on pond fish.
higher total alkalinity where pH values normally range from 7.5
or 8 at daybreak or 9 or 10 during the afternoon. In some water
with extremely high total alkalinity, and particularly in waters
with high total alkalinity and low total hardness, pH values may
rise above 11 during periods of rapid photosynthesis (63).
Obviously, pH measurements should be made in the early
morning and again in the afternoon to assess the typical pH
pattern for a pond. Waters with pH values of about 6.5 to 9 at
daybreak are considered best for fish production. Some ponds
which receive drainage from acid soils or swamps may be too
acid for fish production. Waters with extremely high total
alkalinity may have pH values too high for fish culture. Methods
for increasing or decreasing the pH of pond water will be given
later.
The acid and alkaline death points for pond fish are
approximately pH 4 and pH 11, respectively (63). Even though
fish may survive, production will be poor in ponds with early
morning pH values between 4 and 6 and between 9 and 10,
figure 13. The afternoon pH in many fish culture systems rises to
9 or 10 for short periods without adverse effect on fish.
Carbon Dioxide
High concentrations of carbon dioxide can be tolerated by
fish, although fish avoid levels as low as 5 milligrams per liter.
Most species will survive in waters containing up to 60
milligrams per liter carbon dioxide, provided dissolved oxygen
concentrations are high (30). When dissolved oxygen
concentrations are low, the presence of appreciable carbon
dioxide hinders the uptake of oxygen by the fish. Unfortunately,
carbon dioxide concentrations are normally quite high when dis-
solved oxygen concentrations are low. This results because
carbon dioxide is released in respiration and utilized in
photosynthesis. When dissolved oxygen is low, photosynthesis is
not proceeding rapidly. Therefore, carbon dioxide
concentrations rise because carbon dioxide released by
respiration is not absorbed by phytoplankton for use in photo-
synthesis. Because of the relationship of carbon dioxide to
respiration and photosynthesis, carbon dioxide concentrations
usually increase during the night and decrease during the day.
Particularly high concentrations of carbon dioxide occur in
ponds after phytoplankton die-offs, after destruction of thermal
stratification, and during cloudy weather.
Ammonia
Ammonia reaches pond water as a product of fish metabolism
and decomposition of organic matter by bacteria. In water,
ammonia nitrogen occurs in two forms, un-ionized ammonia
and ammonium ion. Un-ionized ammonia is toxic to fish, but the
ammonium ion is harmless except at extremely high
concentrations. The toxic levels for un-ionized ammonia for
short-term exposure usually lie between 0.6 and 2.0 milligrams
per liter for pond fish, and sublethal effects may occur at 0.1 to
0.3 milligram per liter (25, 52). The pH and temperature of the
water regulate the proportion of total ammonia which occurs
in un-ionized form. A pH increase of 1 unit causes roughly a
tenfold increase in the proportion of un-ionized ammonia (71).
At 28
0
C, the percentages of total ammonia in un-ionized form
are: pH 7, 0.70; pH 8, 6.55; pH 9, 41.23; and pH 10, 87.52.
Fortunately, ammonia concentrations are seldom high enough in
fish ponds to affect fish growth. The greatest concentrations of
total ammonia nitrogen usually occur after phytoplankton die-
offs, at which time pH is low because of high concentrations of
carbon dioxide.
m
CI
10
SII I
Hydrogen Sulfide
Un-ionized hydrogen sulfide at concentrations less than 1
milligram per liter may be rapidly fatal to fish (61). Low pH
favors the presence of un-ionized hydrogen sulfide, and acid
bodies of water which contain high concentrations of hydrogen
sulfide may be improved for fish culture by liming (9).
Fortunately, hydrogen sulfide is seldom a factor in pond fish
culture.
Soils in some areas contain sulfide deposits. Such soils are
usually found where coal is mined or along coastal plains. When
exposed to the air, the sulfide is oxidized to sulfuric acid and
runoff from these soils may have an extremely low pH (27).
Construction of fish ponds should not be encouraged on
watersheds where sulfide bearing materials occur at or near the
surface unless adequate lime is applied to neutralize the acidity.
Total Alkalinity and Total Hardness
The term total alkalinity refers to the total concentration of
bases in water expressed as milligrams per liter of equivalent
calcium carbonate. In natural waters, these bases are primarily
carbonate and bicarbonate ions. Another way to think of
alkalinity is in terms of basicity and resistance to pH change. The
amount of acid required to cause a specified change in pH in a
given volume of water increases as a function of the total
alkalinity levels of the waters. In general, early morning pH is
greater in waters with moderate or high total alkalinity than in
waters with low total alkalinity. The availability of carbon
dioxide for phytoplankton growth is related to alkalinity. Waters
with total alkalinities less than 15 or 20 milligrams per liter
usually contain relatively little available carbon dioxide. Waters
with total alkalinities of 20 to 150 milligrams per liter contain
suitable quantities of carbon dioxide to permit plankton
production for fish culture. Carbon dioxide is often in low
supply in waters with more than 200 to 250 milligrams per liter of
total alkalinity. The afternoon pH in waters with low total
alkalinity may often be as great as in waters with moderate or
high total alkalinity. Waters of low alkalinity are poorly buffered
against pH change, and the removal of carbon dioxide results in
rapidly rising pH.
The total concentration of divalent metal ions (primarily
calcium and magnesium), expressed in milligrams per liter of
equivalent calcium carbonate, is termed the total hardness of
water. Total alkalinity and total hardness values are normally
similar in magnitude because calcium, magnesium, bicarbonate,
and carbonate ions in water are derived in equivalent quantities
from the solution of limestone in geological deposits. However,
in some waters total alkalinity may exceed total hardness and
vice versa. If total alkalinity is high and total hardness low, pH
may rise to extremely high levels during periods of rapid
photosynthesis.
Desirable levels of total hardness and total alkalinity for fish
culture generally fall within the range of 20 to 300 milligrams per
liter. If total alkalinity and total hardness are too low, they may
be raised by liming. However, there is generally no practical
way of decreasing total alkalinity and total hardness when they
are above the desirable level. As a general rule, the most
productive waters for fish culture have total hardness and total
alkalinity values of approximately the same magnitude. For
example, a water with a total alkalinity of 150 milligrams per liter
and a total hardness of 25 milligrams per liter is not as good for
fish culture as a water in which the total alkalinity is 150
milligrams per liter and the total hardness is 135 milligrams per
liter.
Large aquatic plants (aquatic macrophytes) which may grow
in fish ponds are usually undesirable. They interfere with fish
management operations such as seining, feeding, 'and fish
harvest, compete with phytoplankton for nutrients, provide
havens for prey fish to escape predatory fish and thus encourage
unbalanced fish populations, favor mosquito production, and
contribute to water loss through evapotranspiration. Aquatic
macrophytes include filamentous. algae and submersed,
floating-leafed, floating, and emergent macrophytes. Aquatic
macrophytes which begin their growth at the pond bottom are
limited to relatively transparent waters. Therefore,
management procedures which favor plankton turbidity will
often eliminate macrophytes (59). Obviously, floating or
floating-leafed macrophytes must be controlled by other
methods.
Pollutants
Fish ponds are usually constructed in areas where industrial
pollution is not a factor. However, agricultural pollutants, and
especially pesticides, may reach ponds in runoff or drift. Many
pesticides, insecticides in particular, are extremely toxic to fish.
Acute toxicity values for many commonly used insecticides
range from 5 to 10 micrograms per liter and much lower
concentrations may be toxic upon longer exposure. Even if adult
fish are not killed outright, long-term damage to fish populations
may occur in environments contaminated with pesticides. The
abundance of food organisms may decrease, fry and eggs may
suffer mortality, and growth rates of fish may decline.
Pesticides sprayed onto fields may drift over considerable
areas and reach ponds. Therefore, ponds in agricultural areas are
often contaminated to some degree with pesticides. Key factors
in protecting fish ponds from pesticide contamination are:
distance from pesticide treated fields, tree and other vegetative
cover between ponds and fields, topographic barriers to drift or
runoff from treated fields, and proper methods of application of
pesticides to fields. If watersheds receive heavy applications of
persistent pesticides, ponds are not suitable for fish production.
Cotton and other non-food crops are often treated with
especially toxic and persistent pesticides. In some regions,
pesticides which contain heavy metals, such as arsenic and lead,
are still used. Heavy metals may reach ponds and kill fish or
adversely affect production.
WATER QUALITY MANAGEMENT
Inorganic Fertilizers
Inorganic fertilizers used in ponds are the same ones used for
agricultural crops. Nitrogen, phosphorus, and potassium are
termed the primary nutrients in fertilizers. The grade of a
fertilizer refers to percentages by weight of nitrogen (as N),
phosphorus (as P
2
0
5
), and potassium (as K
2
0, also called
potash). For example, a 20-20-5 grade fertilizer contains 20
percent N, 20 percent P
2
05, and 5 percent K
2
0. This method of
expressing nitrogen, phosphorus, and potassium content is
traditional rather than descriptive. Fertilizer does not contain
elemental nitrogen (N), phosphorus pentoxide (P
2
0s), or potash
(K
2
0). The use of N, P
2
0
5
, and K
2
0 to indicate fertilizer grades
originated long ago and has been accepted for practical
purposes. Primary nutrients in fertilizers are usually present as
relatively simple compounds which dissolve to give nitrate,
ammonium, phosphate, or potassium ions. The compositions of
11
Aquatic Weeds
TABLE 6. COMPOSITION OF SOME COMMON INORGANIC
FERTILIZER MATERIALS
Material 
Content, percent
N P
2
0
5  
K
2
0
Ammonium nitrate ...................... 33-35 - -
Ammonium sulfate ....................... 20-21 -
Calcium metaphosphate .................. - 62-64 -
Calcium nitrate ......................... 15.5 -
Ammonium phosphate.................... 11-16 20-48 -
Muriate of potash........................ - - 50-62
Potassium nitrate........................ 13 - 44
Potassium sulfate........................ - - 50
Sodium nitrate.......................... 16 - -
Superphosphate (ordinary) ................ - 18-20 -
Superphosphate (double or triple) ......... - 32-54 -
some common fertilizer materials are given in table 6. Calcium,
magnesium, and sulfur, which occur incidentally or are
intentionally added, are called secondary nutrients in fertilizers.
Trace nutrients, copper, zinc, boron, manganese, iron, and
molybdenum, may also be present in minute amounts in some
fertilizers.
Fertilizers with specific grades are made by mixing
appropriate quantities of nitrogen, phosphorus, and potassium
fertilizers. If all the primary nutrients are included, the mixed
fertilizer is said to be a complete fertilizer. Ingredients needed to
supply the primary nutrients for 100 kilograms of a particular
grade seldom weigh 100 kilograms. A filler is added to make up
the difference in weight. The filler may be an inert material, or it
may be a neutralizing agent, such as limestone, to reduce acidity.
Preparation of 100 kilograms of 8-8-8 from ammonium nitrate
(33.5 percent N), triple superphosphate (46 percent P
2
0
5
s),
muriate of potash (60 percent K
2
0), and filler is illustrated
below:
(1) Calculate the amount of ammonium nitrate (35 percent
N) needed to give 8 kilograms of N
8 kg N + 0.335 = 23.9 kg ammonium nitrate
(2) Calculate the amount of triple superphosphate (46 per-
cent P
2
0
5
s) needed to give 8 kilograms of P
2
0
5
8 kg P
2
0
5 
+ 0.46 = 17.4 kg triple superphosphate
(3) Calculate the amount of muriate of potash (60 percent
K
2
0) needed to give 8 kilograms of K
2
0
8 kg K
2 
O + 0.60 = 13.3 kg muriate of potash
(4) Combined, the three fertilizer materials only weigh 54.6
kilograms, so 45.4 kilograms of filler must be added to give 100
kilograms.
The calculations for preparing mixed fertilizers from basic
source materials are slightly more difficult if one of the source
materials contains two primary nutrients. The appropriate
calculations for preparation of 100 kilograms of 20-20-5 fertilizer
from diammonium phosphate (21 percent N and 54 percent
P20)urea (45 percent N), and muriate of potash (60 percent
K
2
0) are given below:
(1) Calculate the amount of diammonium phosphate (54
percent P
2
0
5
) needed to give 20 kilograms of P
2
0
5
20 kg + 0.54 = 37.0 kg diammonium phosphate
(2) Calculate the amount of N contained in 37.0 kilograms of
diammonium phosphate (21 percent N)
37.0 kg X 0.21 - 7.8 kg N
(3) Since the diammonium phosphate supplies 7.8 kilograms
N, only 12.2 kilograms N are needed from urea. Calculate the
amount of urea (45 percent N)
12.2 kg -0.45 = 27.1 kg urea
(4) Calculate the amount of muriate of potash (60 percent
K
2
0) required for 5 kilograms of K
2
0
5 kg + 0.60 = 8.3 kg muriate of potash
(5) The three ingredients weigh a total of 72.5 kilograms, so
27.5 kilograms of filler must be added for 100 kilograms of 20-20-
5 fertilizer.
In fish culture, it is usually not necessary to mix ingredients
and add filler as illustrated above. The appropriate quantities of
fertilizer source materials may be calculated, weighed, and
applied to the pond. For example, suppose that a 1-hectare pond
must be treated with 20 kilograms per hectare of 10-20-0
fertilizer, and ammonium sulfate (20 percent N) and triple
superphosphate (46 percent P
2
0
5
) are available for use. First,
calculate the amounts of ammonium sulfate and triple
superphosphate as follows:
(1) Since a 10-20-0 fertilizer contains 10 percent N, 20 percent
P
2
0
5
, and 0 percent K
2
0, the amounts of N and P
2
0
5 
in 20
kilograms of 10-20-0 are
20 kg X 0.10 - 2 kg N
20 kg X 0.20 - 4 kg P
2
0
5
(2) Calculate the amount of ammonium sulfate (20 percent
N) which contains 2 kilograms N
2 kg + 0.20 - 10 kg ammonium sulfate
(3) Calculate the quantity of triple superphosphate (46
percent P
2
0
5
) needed to give 4 kilograms of P
2
0
5
4 kg -0.46 = 8.7 kg triple superphosphate
Next, weigh out 10 kilograms of ammonium sulfate and 8.7
kilograms of triple superphosphate and apply these quantities to
the pond.
Inorganic Fertilization and Fish Production
The use of fertilizers to increase fish yields has an agricultural
analogy in the use of fertilizers to favor greater growth of
pasture grasses which, in turn, allows increased production of
livestock. Therefore, the fish culturist should understand some
of the basic principles regulating the beneficial use of fertilizers
in agriculture (69). When a single growth factor is limiting the
growth of a plant, the increase in growth with each equal
successive addition of the growth factor is progressively smaller.
Although slightly more complex, this idea may be extended to
more than one growth factor. In crop production, the
fertilization rate which results in maximum yield is not
12
Fish
production,
kg/ha
I
200 400 800 1,600
Fertilizer, kg/ho per year
FIG. 14. An example of the increase in fish production with
increasing fertilizer application rates. The value in dollars per
hectare of the increase in fish production above the added cost of the
fertilizer is given above the bars representing fish production at
progressively increasing fertilizer rates. For calculations, fertilizer
was given a value of $0.20 per kilogram and fish a value of $1.00 per
kilogram.
necessarily the most economical. After the addition of a few
units of fertilizer, the economic value of the increase in crop
resulting from another unit of fertilizer may be less than the
value of a unit of fertilizer. These same principles apply to fish
production (35, 36). The relationships between fertilizer rate,
fish yield, and economic value of fish and fertilizer are
illustrated in figure 14.
Since plankton production is most often limited by
inadequate phosphorus, phosphate fertilizers are widely used in
fish culture (36, 47). In some ponds, it has been beneficial to
include nitrogen fertilizers along with phosphate fertilizers.
There has also been limited use of potassium fertilizers in fish
production. Increases in fish production resulting from
inorganic fertilization differ greatly, but fish production is
normally increased two to five times through proper use of
fertilizers (29, 36, 62). Some typical increases in fish production
through inorganic fertilization are summarized in table 7.
Experience with fertilization of tilapia ponds in Indonesia (36)
indicated that the most efficient fertilization program was the
application of 45 kilograms per hectare annually of P
2
0
5 
as
superphosphate. In Europe, the annual application of 25 to 30
kilograms per hectare of P
2
0
5
, usually as superphosphate, has
given adequate production of common carp (47). In Israel,
common carp and tilapia ponds are fertilized with 60 kilograms
per hectare of ammonium sulfate and 60 kilograms per hectare
TABLE 7. TYPICAL INCREASES IN FISH PRODUCTION FOLLOWING
FERTILIZATION, THE FACTOR OF INCREASE OBTAINED BY
DIVIDING PRODUCTION IN FERTILIZED PONDS BY
PRODUCTION IN UNFERTILIZED PONDS
Culture species Factor of increase Source
Culture species attributable to fertilizer
Tilapia sp ........................... 3.70 (36)
Tilapia sp., Puntius javanicus,
and Ctenopharyngodon idella ....... 4.38 (36)
Lepomis macrochirus ................ . 3.37 (17)
Cyprinus carpio ..................... 1.72 to 8.32 (33)
0
,600 - -$85
$ 70
$210
,200 -
$600
800 -
400 -
platform and water currents distribute nutrients as they dissolve.
13
I
of superphosphate at 2-week intervals (33, 34). In Alabama, the
most efficient fertilizer schedule for tilapia ponds consisted of
biweekly applications of 22.5 kilograms per hectare of 5-20-5
fertilizer (14). A popular fertilization schedule which is widely
used in the Southeastern United States is outlined below.
(1) In mid-February or early March apply 45 kilograms per
hectare of 20-20-5 fertilizer. Follow with two additional
applications at 2-week intervals.
(2) Make three more applications of 45 kilograms per hectare
of 20-20-5 at 3-week intervals.
(3) Continue applications of 45 kilograms per hectare of 20-
20-5 at monthly intervals or whenever the water clears so that the
Secchi disk visibility exceeds 45 to 60 centimeters.
(4) Discontinue applications by last week in October.
This fertilization program has been widely used and will
produce moderate to dense plankton blooms in most ponds.
However, recent research at Auburn University has
demonstrated that ponds in well-managed pastures often need
no fertilization, while woodland ponds almost invariably need
to be fertilized for good fish production (13); nitrogen and
potassium fertilization is not required in many ponds (18, 23);
and periodic applications of 4.5 kilograms per hectare of P
2
0
5
(10 to 12 applications per year) will give good plankton and fish
production in woodland ponds (23, 43).
It is unreasonable to assume that a single fertilizer application
rate would be the most effective one under all conditions. Ponds
vary greatly in morphometry, hydrology, bottom muds, water
quality, and type of fish culture, so their responses to a given
fertilization program vary greatly. To use an agricultural
analogy, it is common knowledge that fertilizer requirements of
different fields and crops differ greatly. Fertilization
recommendations based on soil analyses have been calibrated
against crop response and the results of soil analyses are used to
establish fertilizer rates. Calibration must be conducted for
individual crops and for specific soil associations (55). The
nature of different pond muds and waters no doubt varies as
greatly as do the characteristics of soils, so a fertilizer rate which
works perfectly well in ponds at Auburn, Alabama, may be
entirely unsuitable for ponds in another locality. Unfortunately,
methods for determining the fertilizer requirements of
individual ponds are not available. The results reported above
may serve as guidelines to establish a suitable fertilization
program for a given pond. The abundance of plankton as
measured by Secchi disk visibility may be used to determine if a
particular fertilizer application rate is suitable. This allows for
adjustments in the rate without having to wait until fish are
harvested to determine if the initial application rate was
successful.
Methods of Application
Large applications of fertilizers at long intervals are wasteful
because much of the phosphorus is adsorbed by the mud (31)
and nitrogen is lost through denitrification (10). In the United
States, fertilizers have traditionally been applied at 2- to 4-week
intervals. Fertilizers may be broadcast over shallow water areas
of the pond, but application is more efficient if the fertilizers are
placed on underwater platforms (41) such as the one pictured in
figure 15. This method of application prevents phosphorus
fertilizer from settling to the pond bottom where the phosphorus
is rapidly adsorbed by mud. Platforms should be about 30
centimeters underwater and one platform is adequate for 2 to 4
hectares of pond area. Fertilizer is simply poured on the
FIG. 15. A fertilizer platform.
Ponds with muddy water or water stained with humic
substances in which the Secchi disk visibility is less than 30
centimeters will not respond to fertilizer nutrients because of
inadequate light for plankton growth. Weed control must be
effected in ponds that are choked with macrophytes, otherwise
fertilizers will stimulate macrophytes instead of plankton. If the
retention time of water in a pond does not exceed 3 or 4 weeks,
fertilizer nutrients willbe flushed out of the ponds before they
produce plankton. Finally, ponds with acid muds and total
alkalinities below 15 or 20 milligrams per liter may not respond
to inorganic fertilization unless lime is first applied.
Some other factors must also be considered when using
fertilizers. New ponds which have never been fertilized may
require more fertilizer than older ponds that have a history of
fertilization. Obviously, fertilization is not effective in flowing
waters. In ponds where fish obtain their food almost entirely
from feeds, little or no fertilizer should be applied. Some
fertilizers are acid forming (urea, ammonium sulfate,
ammonium nitrate) and their continued use may result in
decreased alkalinity and pH. The acidity of nitrogen fertilizers
can be counteracted by liming.
Organic Fertilizers
Organic fertilizers consist of various animal manures or plant
wastes and are usually called manures. Organic materials may
serve as direct sources of food for fish food organisms and fish,
or they may decompose and the inorganic nutrients released
may cause plankton blooms. Organic fertilizers have low N,
P
2
0
5
, and K
2
0 contents, table 8, and tremendous quantities are
required to supply the same amounts of fertilizer nutrients found
in small quantities of chemical fertilizers. When added to ponds,
manures decay and exert an oxygen demand. Thus, excessive
TABLE 8. FERTILIZER CONSTITUENTS IN FRESH MANURE OF SELECTED
FARM ANIMALS - AFTER MORRISON (46)
Average composition, percent
Type of manure
Moisture N P
2
0
5 
K
2
0
Dairy cattle ......................... 85 0.5 0.2 0.5
Beef cattle ........................... 85 .7 .5 .5
Poultry .. ........................ 72 1.2 1.3 .6
Swine ..... ......................... 82 .5 .3 .4
Sheep .............................. 77 1.4 .5 1.2
TABLE 9. PRODUCTION OF BLUEGILL (LEPOMIS MACROCHIRUS) IN PONDS
FERTILIZED WITH ORGANIC FERTILIZERS AND INORGANIC
FERTILIZER - AFTER SMITH AND SWINGLE (60, 62)
Type of fertilization 
Bull,
Cottonseed meal, 1,160 kg/ha ......................... 423
Cow manure, 9,000 kg/ha............................ 272
Kudzu hay, 9,000 kg/ha............................... 176
Inorganic fertilization, 8-8-8, 1,100 kg/ha ............... 341
applications may result in depletion of dissolved oxygen (56).
The rate of oxygen consumption by manure varies with the type
of manure and water quality, so the fish culturist must work out
safe application rates for a particular manure through trial and
error or experimentation.
Organic fertilizers are not widely used in the United States,
but they receive extensive use in many other countries (47, 50).
Manures frequently represent waste products and may be
beneficially used in fish culture. However, because of labor and
transport costs they are usually more expensive per unit of N,
P
2
0
5
, and K
2
0 than chemical fertilizers. Fish production may
be similar or even greater in ponds treated with manures than in
ponds treated with chemical fertilizers, table 9. This is especially
true with species such as the tilapia that will feed directly on the
manure.
Liming
Total Alkalinity and the Need for Lime
Phytoplankton growth in waters with low alkalinity is often
limited by inadequate carbon dioxide and bicarbonate ion.
Some waters of low alkalinity are so acid that fish do not survive
or grow well. Muds in ponds with low total alkalinity are acid
and strongly adsorb the phosphorus added in fertilizer. The
addition of a liming material increases the pH of bottom muds
and makes phosphorus more available. Liming also increases the
availability of carbon for photosynthesis by raising the total
alkalinity of the water. The greater total alkalinity after liming
results in a higher concentration of bicarbonate ion which is in
equilibrium with carbon dioxide. Liming also increases the pH
and total hardness of pond waters. Ponds with total alkalinity
values less than 10 milligrams per liter seldom produce adequate
plankton for good fish production unless they are limed.
Responses to fertilization are variable in unlimed ponds with
waters containing 10 to 20 milligrams per liter total alkalinity,
but unlimed ponds with waters above 20 milligrams per liter
total alkalinity consistently produce adequate plankton after
fertilization to allow good fish production provided all other
factors are favorable (68).
The decision to lime a pond should always be based on total
alkalinity measurements rather than guesswork. Ponds in the
same general area may differ greatly in total alkalinity. For
example, most ponds near Auburn will benefit from liming, but
among these are a few which have total alkalinity values well
above 20 milligrams per liter. The "rule of thumb"
recommendation that all ponds in the vicinity need lime would
result in unnecessary and wasteful application of lime to some
ponds. In determining whether to lime a pond, it should be
remembered that there is no single total alkalinity value below
which lime is undoubtedly needed. Experience has shown that
liming is of little or no benefit if total alkalinity is above 20
milligrams per liter. At total alkalinity values below 20
milligrams per liter, judgment must be used to decide whether to
lime because the need for lime increases with decreasing total
alkalinity. In ponds with total alkalinity values between 15 and
14
FIG. 16. Effect of application of agricultural limestone on total
hardness and total alkalinity in fish ponds. After Arce and Boyd (5).
20 milligrams per liter, the response to liming may be too slight
to justify the effort and expense. Lime should not be used in a
pond that is not to be fertilized because liming alone will not
appreciably increase fish production, except in waters that are
so acid that fish will not survive or grow at normal rates.
Furthermore, lime is seldom needed in ponds where fish are
supplied feed and do not depend on naturally occurring
organisms for food.
When lime is applied to a pond, it reacts with the mud. Until
enough lime is added to satisfy the lime requirement of the mud,
little if any of the added lime will be available to increase the pH,
total alkalinity, and total hardness. A lime requirement
procedure is available for determining the amount of lime
needed to raise the total alkalinity above 20 milligrams per liter
in ponds (12). This procedure is based on a chemical analysis of a
mud sample. Since many fish culturists and biologists will be
unable to use the chemical analysis to obtain a lime requirement
value for their ponds, it is suggested that liming material
equivalent to about 2,000 kilograms per hectare of calcium
carbonate be applied and the total alkalinity determined after 1
or 2 months. If the total alkalinity is still too low, another
application equal in amount to the first should be made and the
total alkalinity measured again. This procedure should be
repeated until enough lime has been applied to maintain the total
alkalinity above 20 milligrams per liter. The addition of liming
material equal to about 2,000 to 6,000 kilograms per hectare of
calcium carbonate should suffice for most ponds. However,
some ponds having high concentrations of organic matter in
bottom muds or sulfide deposits in bottom muds or on their
watersheds may require much greater amounts of lime.
Occasionally the lime application rate may be so high that the
cost of the lime will be prohibitive and the water will be unsuited
for fish culture.
TABLE 10. AVERAGE MUD pH VALUES FOR FIVE LIMED AND FIVE UNLIMED
PONDS- LIME APPLIED BETWEEN FEBRUARY 17
AND MARCH 17, 1973
Type pond 
November August January
1972 1973 1974
Lim ed ............................. 5.2 6.7 6.8
Unlim ed........................... 5.4 5.5 5.5
Mg/liter
as CaCO:
3 
LIMED UNLIMED
50- o----o total hardness 
*-
0 -.--. o total alkalinity *- ----*
9.
"o .0.
40 
: 
00
CL. "0
4)0 
.0 ... c; 
0.0'0
o.d6 ..oO"?"'
30- .'"
00.00
20-A
10
F M A M J
application rate) may be used to avoid having to make large
applications of lime every few years.
15
A. c 0
-RI
P.,
Typical effects of liming may be illustrated by results of
experiments conducted at Auburn University (5). Agricultural
limestone (finely crushed CaMg(CO3)2) was applied to five
ponds at the rate of 4,000 kilograms per hectare and five ponds
served as the unlimed controls. All 10 ponds were fertilized.
Liming caused a marked increase in total hardness and total
alkalinity, figure 16, and an increase in the pH of bottom muds,
table 10.
Tilapia production was 25 percent greater in the limed ponds
than in the control ponds. The total alkalinity of these ponds
before liming averaged 13.5 milligrams per liter. Even greater
responses to liming have been reported in waters which had
lower total alkalinity before liming (17).
Applying Lime to Ponds
Agricultural limestone is the best liming material to use in
ponds. The material should be finely ground (particles should
pass through a sieve with 0.025-centimeter openings) and have a
high neutralizing value. Small particle size is necessary so that
the agricultural limestone will react quickly with water and
mud. The neutralizing values of liming materials refer to the
amounts of acid they will neutralize, expressed as a percentage
of the amount of acid neutralized by an equal amount of pure
calcium carbonate (1). Thus, pure calcium carbonate, with a
neutralizing value of 100 percent, is used as a standard in
referring to liming rates. For example, if using a liming material
having a neutralizing value of 80 percent, to apply at a rate equal
to 2,000 kilograms per hectare of calcium carbonate would
require an application of 2,500 kilograms per hectare (2,000 kg +
0.80) of the liming material.
Hydrated lime (calcium hydroxide, Ca(OH)2) and burnt lime
(calcium oxide, CaO) have higher neutralizing values than
agricultural limestone. If applied in large quantities, however,
these materials cause excessively high pH and fish mortality.
Hydrated lime and burnt lime are sometimes applied to waters
which contain no fish or to muds of ponds which have been
drained to raise the pH and kill fish disease organisms. Basic slag
has been used as a liming material in fish culture, but since its
neutralizing value is lower than that of most agricultural
limestones, extremely large applications are required (75).
Agricultural gypsum (calcium sulfate, CaSO4 -2H20) is not a
liming material, although it has incorrectly been used as one by
some fish culturists.
Liming materials can be easily broadcast over the bottoms of
empty ponds, but application is more difficult when ponds are
full of water. Best results may be achieved by broadcasting the
liming material over the entire pond surface. Bags of liming
material may be emptied from a moving boat. Bulk liming
material is cheaper and may be applied from a plywood
platform attached between two boats, figure 17. Liming
material should be applied during late fall or early winter in
temperate regions so that it will react with waters and muds
before fertilizers are applied in the spring. In tropical regions,
lime should be applied at least 1 month before fertilizer
applications are initiated. This is important because liming
materials will precipitate phosphorus if applied at or near the
same time as fertilizers. However, reaction of liming material
with the mud increases availability of phosphorus fertilizer. The
residual effect of liming is governed by the rate of water loss to
seepage and pond overflow. In ponds with normal rates of water
loss, liming will usually last 3 to 5 years. Once a pond has been
limed, small annual applications (20-25 percent of the initial
/ ~ .. ~
7.
/ .,,
~ 4
__ ~
~i4~ ~
-' 0
A
FIG. 17. A simple method for applying agricultural limestone to a pond which Is full 
of water.
Removal of Clay Turbidity
In somne ponds, it is necessarx to reimoxve the turbidlity caused
by suispendedl clax particles so that lig~ht w ill p~enetrate dleep
enough into the pond for phx topdankton growth. The oldest
technique for remioving clax turb~idity involves the application
of organic matter (38. 67). Rieconiiiendations vary, but the miost
popular include: twxo or three applications of 2,000 kilograiiis pe
hectare of harnxyardl manure: one or inore applications of 2,000
to 4,000 kilograiiis per hectare of hax anol 75 kilograms of
cottonseed mneal plus 2.5 kilogramns of superphosphate per
hectare at 2- to :3-xx ek interxvals. The effectix eness of organic
matter applications in remnoxving clay turhiditx xvaries, and
sev eral xx eeks imist usumally pass before success of a particular
treatment can he determined.
A better method for removxal of clay turhidity is treatmient
wxith filter alim (alumninimu sulfate, Al
2
(S(): ) 14H20). A11111
xx ill cause suspended clax p)articles to coagulate and precipitate
from) the xx ater wxithin at fewv hours (51). The exact application
rate for alum may he determined hy treating sammples of pond
xx ater in heakers \\ ith concentrations of alum ranging fromn 10 to
40 milligrams per liter at 5 milligrams per liter concentration
interxvals. The loxx ext concentration of alumn \k lich causes a floe
of clay p~articles to formn xxithin 1 hour is taken as the dlesiredl
treatment rate. Many fish culturists xill he unable to condumct this
test, hut an appllication of 25 to :30 milligrams per liter xwill
apparently p~recip~itate the clax turidity from most p~onds.
When applying alum, it should he dissolved in xx ater andl quiickly
distrihbuted, pri'torahlN hx spraxying, oxver the entire pond
surface. Application should he mnade during calm, drx wxeather
hecause mnixing by xx ind and rain xxill break up the floc andl
p~revxent it froiii settling out. The results of alum) tireatment in four
pondls are illustrated in table 11. Alum has an acidl reaction in
xx ater, so it destroxys total alkalinitx and reduces JAI1. Each in1illi-
grain per liter of alumn xwill (decrease the total alkalinitx bx 0.5
milligramn per liter. If the total alkalinity of xx ater is heloxx 20
milligrams l)er liter, aluiii treatment muay depress the p11I to the
p~oint that fish are adxversely affected. lHydrated lime (calciumn
hx droxide, Ca (01)) a ,pplied simultaueouslx at the rate of 0.40
iilligran iier liter for each 1.0 miilligram per liter increment of
alhim xx ill p~rexvcut umofax orahle changes in alkalinity and 1)11.
Another alternativ e is to lime pond~s xx ith xx aters of loxxalkalinitx
hefore treating xx ith alum, Liming iiaterials xxill often
p)recipitate clay turbiditxy, hut if turbiditx pxersists after liiiing,
alumn treatment nmay he conducted xx ithout (danger ouf 1)11 de-
p~ression.
Although alumn treatment xxill clear pond xxater of clax
turhidit\ , it dloes nothing to correct the cause of turhidity .('nless
the source of the tuirbidity is eliminated, ponds xx ill again
hecome tuirhid xx'ith clay p)articles. (lax turbiditx usuallx results
b~ecause ponds receix e large x olnimes of tuirbid runoff after 
each
rain. Erosion of the xx'atershecl ma\ he prexvented byx
rex egetation. If this is impossible, it is somietimnes pxossible 
to
dlixvert the turbidl runoff from the pxond by use of a (lixversion
dlitch.
Reduction of pH
WXaters wxith high total alkaliniities and loxw total hardnesses
ii ax haxve dlangerouslx high 1)11 xvalues (luring p~eriods of rapid
phytoplankton groxx th. Although xx aters of this ty pe (10 not
occur often, an analy six should he imade to deterine 
if the
potential for high 1 exists.
Liming to increase total hardness is of imo xvaloe in prevxenting
hiigh p11 because Ii ine applicat0in increa sex toital alkali mni tx and
total hardness hx roumgly the sailie amount . Applications of
ainmoniuii fertilizers haxve been recommnedl~ to loxwer the 1)11
of p~ondl wxater. The aiiimtniii ion in fertilizer is initrified1 to
TI si 11. E' ii A s It \1 i(A Xii xiiv: xi So i I I imxixiiox(Ix
1' 0(11 ) I\ Fl~i P()i mli
Alum 1 u rh ditx units lieduiction
Pnd ap1 iplied mu turbiditv
1 i igliter Bct ore treat iu iit After treatment pe rcent
E-67 . 15 401 2 9
V68 ... 20 28 :3 89
E- 73 . ... 20) 19 :3 84
S-27 ... 20) 83 21 9
nitrate NN ith the release of hydrogen ion wxhich lowxers the 1)11.
Hoxwe\ er, at high pHI a large p)ercentage of the ailinonium ion
appl)ied to a pond xx ill immediately be transformed to tin-
ionized ammnonia, -w hich is high]\- toxic to fish. Filter almin
(aluinutm sulfate) may be adlded to ponds to decrease p11. An
ahim treatment equal in inillhgrams per liter to the
phenodphithalein alaiiywl educe the pH to ap~proximnately
8..3. Although ahinm treatment may he used to prexvent a fish kill
wxhen the pH is too high, it does nothing to change the conditions
resp~onsible for high p)H.
Agricultural gy psumi (calcium sulfate) may he applied to
wxater to increase the total hardness xwithout affecting the total
alkalinity. Experience indicates that gy 1)5in wxill allev iate the
conditions responsible for high pH, hut confirmatorx research is
needed. The hest treatmnent rate for agricultural gy psum
app1ears to he the amount xxhich xx ill increase the total hardness
to a lev el xx here it equals the total alkalinity . The treatment rate
may he determined from the folloxxing equation:
agricultural(ttlaklnttoahadesX2.
gyplsnim (mig/liter) (oa laiixttlhrn~ .
The agricultural gx psumi should he applied in the sanme manner
as liming materials. The residual effect of gx lsuuin treatment is
not knowxn.
FIG. 18. A small spray-type surface aerator.
Dissolved Oxygen
Almost all problemns xx ith dissolved oxygen in fish culture are
the consequences of heavyx plankton hlooms. In fertilizedl ponds,
fertilization should he halted xxhen p~lankton hloomms get too
(dense (i.e., Secchi disk readings of Z5 centimueters or less). In
p)onds xx here fish are supplied feeds, heax x plankton hlooms are
the natural consequences of high feeding rates. Loxx er feeding
rates xxvill result in less plankton groxwth, hrit only at the expense
of decreased fish production. Suitahle plankton densities result
in Secchi dlisk visibilities of 30 to 60 centimeters. The prohahility
of prohlems xx ith loxx dissolxved oxy gen concentration increases
as the magnitude of the Secchi dlisk v isihilitxy decreases heloxx 30
centimeters. In ponds xxith Seechi disk xvisihility values of 10 to
20 centimeters, dIissolxved oxy gen concentrations may fall so loxx
at night that fish are stressed, and a cloudy day mnay lead to
dlissolxved oxy gen depletion the followxing morning (53).
A numher of procedures are used to p~reven~t fish kills xx hen
dissolv ed oxy gen concentrations are dangerouslx loxx
App)lication of uip to 6 or 8 milligrams per liter of potassium
p)eriaugamiate has heen frequenitly rcomjnuumnded ini the 1.Unite~d
States (42). The potassium p)ermanganate is supposed to oxidize
organic matter and loxxer the demand for dissolved oxy gen in
the p)ond. Recent research (72) has demnustrated that p~otassium
p)ermianganate is entirely xxvorthless for this purpose andl that its
application actually increases the length of time required for
dissolxved oxygen concentrations to return to normal lev els.
Applications of calcium hy droxide haxve heen recommended to
destroy organic matter in ponds xx ith loxx- dissolxved oxygen
concentrations and therehx reduce rates of oxy gen consumption
hx hacteria. There is no reason to helieve that applications of
calciumi hy droxide xx ill loxxer concentrations of organic, matter.
Howxevxer, xxhen dissolved oxygen is loxx, carbon dlioxidIe is
usually quite high. The application of calciumi hydroxide xx ill
remnoxe carhon dioxide xxhich xx ill alloxw fish to hetter utilize the
loxx' concentration of dlissolv ed oxy gen. Each milligram per liter
of carhon dioxide xvill require 0.84 uxilligrarn per liter of
calciunm hvd(roxidle for its remoxval. For example, if a pond
contains 25 milligrams iper liter of carhon dioxide, a calciumi
hy droxide treatment of 21 inilligranis per liter (25 X 0.84) xxomld
remove the carhon (dioxide. Folloxxing phy toplankton (lie-offs,
applications of fertilizers haxve heen employed to encourage
phytoplankton groxxth and encourage dlissolved oxygen
production. Research to document the effectiveness of this
FIG. 19. A Crisafulli pump and sprayer.
P
,~
7)
*1a
FIG. 20. A paddiewheel aerator.
I)rocedmlre has not been condluctedl, hut nutrient 
conicentrationis
are already high in I)ionlds folloxwing p)h) toplankton (lie-oftfs 
and
it is doubtful that fertilization is necessarx.
The only reallx effectixve p~rocedlure for p~rex 
enting fish
nortalitN (liring p~eriodls of extreinex low 
(dissolvxed oxy genl
invoilves the use of mechanical (devices (28, 45). 
Large, tractor-
lpoveredl puiil)s niax be used to pumpl fresh, ox\ genated 
wvater
fromn a nearby poind into the pondi( 
\N ith low dissolxved oxvgeni
concentrations. Alternatix elx x water frin 
xxelI, spring, or stream
mnax be releasedl into) the o~xygen (depleted 
p~ond. WXell wxater
should be dischargedl across a baffle for aeration 
because xNx~
wxat(er is oif ten high in carbiin dioxide and (lef 
icient in dissolx ed
ioxygen. NN lien oxxygenatedl xvater is released] 
into~i pondi~ wxith
oixygen depletion, bottomn xx ater wxhich 
contains less dissolxed
oixygen andl iire carbon dioxide than 
surface wxater should
simiultaneous'l be releaserd froii the pond 
if possible. PuniIps
mnay also be usedl to remoxve wNater fromt the 
p~ond xx ith lowv
dlissoilxved oixygen anrl release it xwith force back 
onto the surface
oif the same pond. The agitation and 
circulation of the water
increases its dissolxved ox,, gen conitent. I low 
exer, this miethod is
not as effectixve as pumpling fresh, oxy genated 
wxater from
another pond or xvelI into the pond xxith 
loxv (dissolvxed oxxygen.
Various types of aeration devices may be 
used to introduce
oxxygen into wxaters xxvith loxw dissolved 
oxygen concentrations.
Small sp)ra\ -type surface aerators are in conninon 
use, figure 18.
These aerators are most effectixve in smiall ponds 
or xxhen sev eral
aire operated in a large pond. More poxx erful aerators, 
such as the
Crisafulli pumip andI spray er, figure 19, andl 
the p~addlexxheel
aeratoir, figure 20, supply considerably inure 
dissolxved oixygen
to ponds than the spray-tx pe surface aerators. 
liixxex'er,
Crisafulli luiiis andI padldlexwheel aerators are 
exp~ensixve and
mnust be operated fromn the poxxer take off 
of at farm tractor.
Large fish farmis and research stations can afford 
to maintain andl
olperate emergency aeration equipment, but smnall 
scale fish
culturists haxve little recourse wxhen faced xx ith 
rdissolvedl oxygen
p~roblems. Fortunately, problemis xx ith dissolved 
oxy gen) seldomn
occur excepit in ponds xxhere fish are fed at high rates.
Fish culturists often nionitor dissolxved oxy gen concentrations
(luring the night in ponds to determine if emnergency 
aeration is
neededl. Recent research has resulted in 
procedures for
p~redlicting hoxx loxw dissolxved oxxygen concentrations 
xwill fall
(hiring the night (20, 53, 54). Suich p~redictions 
permit the fish
cullturist to p)repare for emergency aeration 
in adxvance. The
simpulest oif these procedures involxves the 
measurement of
dissolved oxygen concentrations at dusk and 2 or 
3 hours later.
These two xvalues atre plIotted versuls timeit 
oil a graph and a
straight line is p~rojectedl through the two points 
and( used to
estiimate the (lissolv ed oxy gen concentration 
at later hours
(luring the night. The use of this technique is illustrated 
in figure
21.
Dissolved
oxygen,
mg/liter
10-
9- 
measured
8 values
7 N
5N
4 N
N projected
N value
0
8 p.m. 12 pM. 4am.
FIG. 21. A graphical method for predicting the 
nighttime decline In
dissolved oxygen concentration In fI sh ponds. After Boyd 
et ai. (20).
Fish Feeding and Water Quality
Fish eat most o~f the feed applied to ponds, 
but on a dlry matter
basis only about 295 per cent iif the nutrients iii 
the feed is
conx erted to fish flesh (P1). The rest o~f the 
nutrients reach the
water as inetabolic wvaste. This 
wxaste includes carbon (dioxide,
ammnonia, p)hosphate, and iother inorganic 
and] organic
substances. These nutrients stimulate p~lanktion p~roductioin, 
and
the amiount of organic matter p~roduced by photosxynthesis 
will
exceed by sev eral timies the amiount of organic 
mnatter reaching
the water in metabolic xx aste (11). The density 
of p~lankton in a
pond is closelx related to the feeding rate. For 
example, during
the course of the groxx ing season the feeding rate 
was gradually
increasedl in catfish ponds resulting in a corresp)ondling 
(decrease
i~
x's.
Dissolved Secchi disk
oxygen, visibility,
mg/liter cM
10 -100
8 Secchi 
disk -80
visibility
6 
-60
dissolved
4 oxygen - 40
2 
-20
0 0
I I I I I I
10 20 30 40 50
Feed, kg/ha per day
FIG. 22. Secchi disk visibilitles and early morning (6:30 a.m.)
dissolved oxygen concentrations In a channel catfish pond as the
feeding rate was gradually Increased from May to September.
in Secchi disk visibilities, figure 22. Along with the decrease in
Secchi disk visibilities, there was a decrease in the early morning
dissolved oxygen concentrations, figure 22. Similarly, average
plankton density increased and average concentrations of
dissolved oxygen in the early morning decreased with greater
feeding rate in catfish ponds with low, medium, and high
feeding rates, table 12.
TABLE 12. AVERAGE EARLY MORNING DISSOLVED OXYGEN CONCEN-
TRATIONS AND SECCHI DISK VISIBILITIES IN CHANNEL CATFISH
PONDS WITH DIFFERENT FEEDING RATES
Early morning Secchi disk
Feeding rate 
dissolved oxygen, 
visibility,
mg/liter cm
Low (34 kg/ha per day) ........ 4.71 68
Medium (56 kg/ha per day) 2.95 45
High (78 kg/ha per day) ....... 1.95 21
Obviously, the frequency of dissolved oxygen problems
increases with feeding rate. Thus, the ultimate limit on feeding
rate and on fish production is set by water quality. As a general
rule, fish production increases linearly with feeding rate while
water quality deteriorates exponentially with feeding rate.
Aquatic Plant Control
As mentioned earlier, one effective technique of controlling
many species of macrophytes is through fertilization to produce
plankton turbidity and shade the pond bottom. This technique is
especially powerful if ponds are constructed so that no areas are
shallower than about 60 centimeters. Grass carp (white amur)
eat tremendous quantities of aquatic vegetation and provide a
biological method for controlling macrophytes. When stocked
at 60 to 80 per hectare, grass carp will control most species of
macrophytes that cannot be controlled by plankton turbidity.
Grass carp are even effective in controlling macrophytes in
ponds that are not turbid with plankton. In small ponds,
macrophytes may be controlled by cutting or by dragging them
out with a rake or seine.
Herbicides are also used in fish culture to control
macrophytes. The manufacturer's label gives the rate and
method of application for a herbicide. The label provides
information on safety precautions. Usually, the concentrations
of aquatic herbicides used to kill macrophytes are safe to fish.
Decay of macrophytes killed by herbicides can cause dissolved
oxygen depletion. If ponds have extensive areas of
macrophytes, one-fourth to one-fifth portions of the pond
should be treated at 1- to 2-week intervals to reduce the chance
of dissolved oxygen depletion. The major limitation of
herbicides for controlling macrophytes is that once the
concentration of a herbicide declines to a non-toxic level,
macrophytes will regrow. Thus, repeated applications of
herbicides are required to control macrophytes, often at
considerable expense.
Algicides are sometimes used to control phytoplankton in
ponds. Copper sulfate, the most widely used algicide, will kill
most species of phytoplankton at concentrations of 0.1 to 0.5
milligram per liter in waters with total alkalinities below 40 or
50 milligrams per liter (70). In waters with higher alkalinities,
copper sulfate concentrations of 1.0 milligram per liter or more
may be required to kill phytoplankton. Copper sulfate may be
applied by dissolving it in water and distributing it over the pond
surface. Alternatively, copper sulfate crystals may be placed in a
burlap bag and the bag towed behind a boat until the copper
sulfate dissolves. Burlap bags of copper sulfate may be
positioned in ponds so that the chemical gradually dissolves and
mixes with the water (22). Copper sulfate may also be used to
treat scums of phytoplankton which drift to the leeward sides of
ponds (40).
Phytoplankton killed by copper sulfate decomposes rapidly
and may result in low dissolved oxygen concentrations. Copper
sulfate has no appreciable residual toxicity and phytoplankton
growth will resume soon after treatment. Fish are susceptible to
copper sulfate, and in waters with alkalinities less than 20
milligrams per liter, treatment with 0.5 to 1.0 milligram per liter
of copper sulfate may kill fish.
Synthetic algicides, such as Diuron (3-(3, 4 dichlorophenyl)-1,
1-dimethyl urea) and Simazine (2-chloro-4, 6-bis
(ethylamino)-triazine), are sometimes used to kill
phytoplankton. These algicides are extremely toxic to algae,
have a long residual action, and are not toxic to fish at
concentrations used to kill phytoplankton. As with copper
sulfate, extensive mortality of phytoplankton following
applications of synthetic algicides may result in depletion of
dissolved oxygen. Some fish 
culturists have attempted to 
"thin"
phytoplankton blooms by small, periodic applications of
synthetic algicides to ponds receiving heavy applications of
feed. However, recent research (73) demonstrated that this
practice results in prolonged periods of low dissolved oxygen
concentrations and reduced fish yields.
Calculations for Chemical Treatments
Concentrations for chemical treatments of ponds are given in
milligrams per liter so fish culturists must calculate how much of
a chemical to add to a pond to give the desired concentration. To
calculate the amount of a chemical needed, the volume of the
pond must be known. Assuming the surface area of a pond is
known, the simplest technique for obtaining the average depth
to use in computing the volume is to make transects (8 or 10 will
usually suffice) across the pond in a boat while making depth
19
soundings at regular intervals with a calibrated rod or sounding
line. The average of all soundings is taken as the average depth.
Once the volume of a pond is known, it is a simple matter to
calculate treatment rates. For calculations of pond treatments,
one must realize that 1 gram per cubic meter is equivalent to 1
milligram per liter. The following examples illustrate how to
calculate amounts of chemicals to add to ponds.
Example. A pond has a surface area of 0.26 hectare and an
average depth of 1.15 meters. How much filter alum (100
percent pure) must be applied to the pond to give an alum
concentration of 25 milligrams per liter?
(1) Since 0.26 hectare = 2,600 square meters, the pond
volume is:
2,600 m
2 
X 1.15 m = 2,990 m
3
(2) Each cubic meter will require 25 grams of alum for a
concentration of 25 milligrams per liter, so the amount of alum
needed for the entire pond is:
2,990 m
3 
X 25 grams/m
3 
= 74,750 grams
(3) A treatment of 74,750 grams equals 74.75 kilograms.
Example. The average depth of a pond is 0.57 meter and the
surface area is 0.01 hectare. How much agricultural gypsum (80
percent pure) must be applied to produce a gypsum
concentration of 50 milligrams per liter?
(1) Since 0.01 hectare = 100 square meters, the pond volume
is:
100 m
2 
X 0.57 m = 57 m
3
(2) Each cubic meter will require 50 grams of gypsum for a
concentration of 50 milligrams per liter, but the agricultural
gypsum is only 80 percent pure. Therefore, we may calculate the
concentration of gypsum as follows:
50 grams + 0.80 62.5 grams
The amount of agricultural gypsum needed for the entire pond
will be:
57 m
3 
X 62.5 grams/m
3
= 3,562 grams or 3.56 kg
Example. A pond with a volume of 1,000 cubic meters must be
treated with a herbicide. The herbicide is a liquid with 75
percent active ingredient and a density of 0.85 gram per milliliter
(0.85 kilogram per liter). How much of the liquid herbicide must
be applied to the pond to give a concentration of 1 milligram per
liter of active ingredient?
(1) The amount of the active ingredient to give a
concentration of 1 milligram per liter is:
1,000 m
3 
X 1 gram = 1,000 grams = 1.0 kg
(2) The herbicide has an active ingredient content of 75
percent, so the weight of herbicide containing 1.0 kilogram
active ingredient is:
1.0 kg - 0.75 = 1.33 kg
(3) The density of the herbicide is 0.85 kilogram per liter, so
the volume of the herbicide weighing 1.33 kilograms is:
1.33 kg + 0.85 kg/liter = 1.56 liters
Thus, 1.56 liters of the liquid herbicide would give a
concentration of 1 milligram per liter of the active ingredient
when applied to the pond.
Chemicals which are applied to ponds come in a variety of
formulations including crystals, solutions, wettable powders,
emulsifiable concentrates, and granules. Fish culture stations
and large fish farms can afford rather elaborate equipment for
applying chemicals. For example, chemicals may be dissolved
in a tank of water or some other solvent and sprayed over the
surface with a power sprayer. Liquids may be dispersed
uniformly from a boat mounted tank through a boom consisting
of a pipe with a series of small diameter holes in its underside. A
valve regulates the rate at which the solution is fed by gravity
into the water, or a pump may be used to effect more uniform
and forceful release. Dispensers for granules or powders may
consist of hoppers with adjustable dispensing holes in the
bottom. An auger is employed to prevent clogging of holes.
Finally, chemicals may be released into the wash of an outboard
motor propeller to effect mixing as the boat moves over the
pond surface.
In instances where the owner of one or a few ponds must
apply chemicals, it is usually not practical to purchase or
construct an elaborate dispenser. The chemical can be dissolved
or mixed in a large container of water and applied to the pond
surface. Application may be accomplished with a pressurized
garden sprayer, or the solution or mixture may be splashed with
a dipper over the pond surface. Care should be taken to dispense
the chemical as uniformly as possible. Granules may be
broadcast by hand or with a small "cyclone" seeder. Crystals
may be placed in a burlap bag and the bag towed behind a boat
until they have dissolved. Only a little ingenuity is needed to
develop a method for applying a chemical to a pond once the
treatment rate has been established.
WATER ANALYSIS
Water analysis is a highly specialized field and methods for
measuring the concentration of almost any possible constituent
of water are available. These methods may be found in several
standard water analysis manuals. The most widely used of these
manuals is the Standard Method for the Examination of Water
and Wastewater (3). To make water analyses according to
standard procedures, a water analysis laboratory and a well
trained analyst are essential. In practical fish culture, however,
only a few water quality data are needed in making water
quality management decisions. These normally include pH,
total alkalinity, total hardness, dissolved oxygen, carbon
dioxide, and plankton abundance. Water analysis kits, such as
the one illustrated in figure 23, are available at a modest cost.
The kits provide sufficiently accurate data on which to base
management decisions (15). A Secchi disk, which may be
constructed from common items or purchased for a small cost,
may be used to estimate plankton abundance.
Sampling Water
Water samples for dissolved oxygen or carbon dioxide
analyses must be collected so that they do not come in contact
with the atmosphere. If a sample is supersaturated with
dissolved gases, the gases are lost to the atmosphere. Samples
below saturation will gain gases from the atmosphere. A number
of samplers are available for collecting water for dissolved gas
analyses, but the least expensive types may be obtained from the
20
'a
FIG. 23. A small water analysis kit suitable for use in fisheries management.
FIG. 24. A small sampler for taking samples for dissolved gas
analysis.
manufacturers of water analysis kits. A small sampler for
dissolved gases is shown in figure 24. Samples for total alkalinity,
total hardness, or pH may come in contact with the air without
introduction of appreciable errors in measurement. Samples of
surface water may be secured by simply imrnersing an open-
mouthed bottle and allowing it to fill. Samplers may also be
constructed for obtaining water from greater depths. For
example, a stoppered bottle may be attached to a wooden stick
and lowered to the desired depth. The stopper is then jerked out
with an attached cord so that the bottle rmay fill. This sampler is
illustrated in figure 25. A slightly more elaborate sampler for
taking water from specific depths is shown in figure 26. The
bottle is lowered to the desired depth and the stopper is
remioved by a sharp tug on the line. Once the water sample has
been collected it should be analyzed as soon as possible to
prevent changes in concentrations of the constituents of interest.
Water Analysis Kits
The largest and best known manufacturer of water analysis
kits is probably the Ilach Chemical Company of Ames, lowa,
and Loveland, Colorado. However, kits of comparable quality
may be obtained from other companies, so the use of the Hach
water analysis kits in the illustrations is by no means an
endorsement of Hach Chemical Company products. In using
kits, the directions should be followed carefully and all
operations conducted with as much precision as possible. Slight
errors in measuring the volumes of samples or titrating agents
FIG. 25. Water sampler useful for collecting water from depths of up
to 2 meters.
FIG. 26. A weighted bottle water sampler.
hooks
To obtain the Secchi disk visibility, lower the disk into the
22
eye bolt
latcl
rubber stopper
eye hook
weight
I sfu orc
will be greatly magnified in the final results. For measuring total
hardness or total alkalinity on samples with low concentrations
(below 20 or 30 milligrams per liter) of these constituents, the
volumes of samples and reagents should be increased by five
times to get reliable results. Measurements of pH with water
analysis kits are 0.5 to 1.0 pH unit higher than the correct values
obtained with a pH meter. The reagents in water analysis kits
deteriorate with time and should be replaced every 6 to 12
months. In spite of the limitations of water analysis kits, they are
often the only method available for water analysis in fish culture,
and with reasonable care the kits will provide useful data. In
table 13, comparisons are made between data obtained on the
samples by a Hach Model AL-36B water analysis kit, figure 23,
and by standard laboratory procedures.
TABLE 13. COMPARISON OF DETERMINATIONS MADE ON WATER SAMPLES
BY STANDARD METHODS (3) AND A HACH WATER ANALYSIS KIT
(MODEL AL-36B) - AFTER BOYD (15)
Procedure 
Sample
A B C D
Total alkalinity (mg/liter)
Standard method .................... 11.0 31.8 49.6 119.7
Hach kit ............................ 15.6 33.7 49.4 116.3
Total hardness (mg/liter)
Standard method ..................... 7.7 27.1 53.4 107.5
Hach kit ......................... 11.1 32.7 55.7 110.4
Carbon dioxide (mg/liter)
Standard method ..................... 1.2 4.3 10.9 18.0
Hach kit ............................ 5.0 5.0 10.0 15.0
Dissolved oxygen (mg/liter)
Standard method ..................... 1.1 2.7 4.9 8.6
Hach kit ............................ 2.0 2.8 4.0 8.0
pH
Standard method ..................... 4.5 5.5 7.8 8.8
Hach kit ............................ 5.0 6.1 9.0 9.7
More advanced, and expensive, water analysis kits are
available, figure 27. These kits have the capacity for measuring
dissolved gases, pH, ammonia, nitrate, nitrite, phosphate,
sulfate, chloride, conductivity, and several other water quality
variables. The more elaborate kits are suitable for fishery
management work and for some types of research in fish culture
(16).
Secchi Disk Visibility
A Secchi disk is 20 centimeters in diameter, painted with black
and white quadrants, and attached to a calibrated line, figure 28.
The disk is weighted on the underside with a lead plate so that it
will sink readily. Secchi disks may be purchased from scientific
supply houses or constructed from sheet metal, plexiglass, or
masonite. A flat paint should be used to prevent glare. A suitable
alternative to attaching the disk to a calibrated line is to attach it
from its center to a vertical meter stick. Secchi disk visibilities
seldom exceed 100 centimeters in productive fish culture
systems, so measurements will seldom be limited because of the
length of the meter stick.
Secchi disk visibility is not a suitable estimate of plankton
unless plankton is the primary source of turbidity. An
experienced observer can readily distinguish between plankton
turbidity and other forms of turbidity. However, the novice
must remember that plankton blooms are not always green.
Plankton blooms may also impart yellow, red, brown, or black
coloration to water. Usually plankton organisms are large
enough that their particulate nature is obvious if water and its
contents are viewed against a white background.
N
~~%;
'4a
/
SI
'4
FIG. 27. A large water analysis kit used in fisheries management and occasionally In fisheries research.
water until it just disappears and record the depth. Lower the
disk a little mnore and then raise it until it just reappears and
record the depth. In making these measurements, view the disk
fromn directly above. The average of the two depth readings is
the Secchi disk visibility. Conditions for taking Secchi disk
eye bolt measurements 
should be standardized. A good practice is 
to
20cm bmake measurements on calm days between 9 a.m. and 3 p.mn. If
20cm possible, make readings 
when the sun is not behind clouds. Make
eight measurements on the lee (downwind) side of the boat with the
sun behind you. Even when conditions are carefully
standardized, Seechi disk visibilities obtained at the same time
bv different observers for the samne body of water will vary
slightly. Furthermore, the same observer mia.y obtain slightly
raduted rope different readings 
if the disk is viewed in the samne pond 
at
grauaeddifferent times of the day. In practice these slight variations are
not critical. In the absence of a Secchi disk, any white object or
even the palmn of your hand can be used to judge turbidity in
FIG. 28. A Secchi disk. 
pond waters.
I- K /
%4 
0

BIBLIOGRAPHY
(1) ADAMS, F. AND C. E. EVANS. 
1962. A Rapid Method for Measuring
Lime Requirement of Red-Yellow Podzolic Soils. Soil Sci. Soc.
Amer. Proc., 26: 355-357.
(2) ALMAZAN, G. AND C. E. BOYD. 1978. An Evaluation of Secchi Disk
Visibility for Estimating Plankton Density in Fish Ponds. Hydro-
biologia. In press.
(3) AMERICAN PUBLIC HEALTH ASSOCIATION, AMERICAN WATER
WORKS ASSOCIATION, AND WATER POLLUTION CONTROL
FEDERATION. 1975. Standard Methods for the Examination of
Water and Wastewater, 14th ed. American Public Health Assoc.
Washington, D.C. 1,193 pp.
(4) ANDREWS, J. W., T. MURAI, AND G. GIBBONS. 1973. The Influence
of Dissolved Oxygen on the Growth of Channel Catfish. Trans.
Amer. Fish. Soc., 102: 835-838.
(5) ARCE, R. G. AND C. E. BOYD. 1975. Effects of Agricultural Lime-
stone on Water Chemistry, Phytoplankton Productivity, and
Fish Production in Soft Water Ponds. Trans. Amer. Fish. Soc.,
104: 308-312.
(6) BARDACH, J. E., J. H. RYTHER, AND W. O. MCLEARNEY. 1972.
Aquaculture. Wiley-Interscience. N.Y. 868 pp.
(7) BARICA, J. 1975. Summerkill Risk in Prairie Ponds and Possi-
bilities of its Prediction. J. Fish. Res. Bd. Canada, 32: 1,283-1,288.
(8) BEASLEY, P. G. 1963. The Penetration of Light and the Concen-
tration of Dissolved Oxygen in Fertilized Pond Waters Infested
with Microcystis. Proc. Ann. Conf. Southeastern Assoc. Game
and Fish. Comm., 17: 222-226.
(9) BoNN, E. W. AND B. J. FOLLIS. 1967. Effects of Hydrogen Sulfide
on Channel Catfish, Ictalurus punctatus. Trans. Amer. Fish.
Soc., 96: 31-36.
(10) BOULDIN, D. R., R. L. JOHNSON, C. BURDA, AND C. KAO. 1974.
Losses of Inorganic Nitrogen from Aquatic Systems. J. Environ.
Qual., 3: 107-114.
(11) BOYD. C. E. 1973. The Chemical Oxygen Demand of Waters
and Biological Materials from Ponds. Trans. Amer. Fish. Soc.,
102: 606-611.
(12) . 1974. Lime Requirements of Alabama Fish Ponds.
Auburn Univ. (Ala.) Agr. Exp. Sta., Bull. 459. 20 pp.
(13) . 1976. Water Chemistry and Plankton in Unfertilized
Ponds in Pastures and in Woods. Trans. Amer. Fish. Soc., 105:
634-636.
(14) . 1976. Nitrogen Fertilizer Effects on Production of
Tilapia in Ponds Fertilized with Phosphorus and Potassium.
Aquaculture, 7: 385-390.
(15) . 1976. Evaluation of a Water Analysis Kit. Auburn
Univ. (Ala.) Agr. Exp. Sta., Leaf. 92. 3 pp.
(16) . 1977. Evaluation of a Water Analysis Kit. J. Environ.
Qual., 6: 381-384.
(17) . 1979. Water Quality in Warmwater Fish Ponds.
Auburn Univ. (Ala.) Agr. Exp. Sta. In press.
(18) AND J. W. SOWLES. 
1978. Nitrogen Fertilization of
Ponds. Trans. Amer. Fish. Soc., 107: 737-741.
(19) , E. E. PRATHER, AND R. W. PARKS. 1975. Sudden
Mortality of a Massive Phytoplankton Bloom. Weed Sci., 23:
61-67.
(20) , R. P. ROMAIRE, AND E. JOHNSTON. 1978. Predicting
Early Morning Dissolved Oxygen Concentrations in Channel
Catfish Ponds. Trans. Amer. Fish. Soc., 107: 484-492.
(21) CLAY, D. 1977. Preliminary Observations on Salinity Tolerance of
Clarias lazera from Israel. Bamidgeh, 29: 102-109.
(22) CRANCE, J. H. 1963. The Effects of Copper Sulfate on Microcystis
and Zooplankton in Ponds. Prog. Fish-Cult., 25: 198-202.
(23) DoBBINS, D. A. AND C. E. BOYD. 1976. Phosphorus and Potassium
Fertilization of Sunfish Ponds. Trans. Amer. Fish. Soc., 105:
536-540.
(24) DOUDOROFF, P. AND D. L. SHUMWAY. 1970. Dissolved Oxygen Re-
quirements of Freshwater Fishes. FAO Fisheries Biology
Technical Paper, No. 86. 291 pp.
(25) EUROPEAN INLAND FISHERIES ADVISORY COMMISSION. 1973. Water
Quality Criteria for European Freshwater Fish. Report on
Ammonia and Inland Fisheries. Water Res., 7: 1,011-1,022.
(26) FISHLESON, L. AND D. POPPER. 1968. Experiments on Rearing Fish
in Salt Waters near the Dead Sea, Israel. Proc. World Symposium
on Warmwater Pond Fish Culture. FAO, Fisheries Rept. No. 44,
5: 244-245.
(27) FLEMING, J. F. AND L. T. ALEXANDER. 1961. Sulfur Acidity in South
Carolina Tidal Marsh Soils. Soil Sci. Soc. Amer. Proc., 25: 94-95.
(28) GRIZZELL, R. A., JR., O. W. DILLON, JR., AND E. W. SULLIVAN. 1969.
Catfish Farming, A New Crop. USDA, Farmer Bull. 2244.
Washington, D.C. 22 pp.
(29) GROVER, J. H., R. D. RECOMETA, AND V. A. DUREZA. 1976. Pro-
duction and Growth of Milkfish, Common Carp, and Catfish in
Fertilized Freshwater Ponds. Kalikasan, Philippines. J. Biol., 5:
193-206.
(30) HART, J. S. 1944. The Circulation and Respiratory Tolerance
of some Florida Freshwater Fishes. Proc. Fla. Acad. Sci., 7:
221-246.
(31)
(32)
HEPHER, B. 1958. On the Dynamics of Phosphorus Added to Fish
Ponds in Israel. Limnol. Oceanogr., 3: 84-100.
. 1962. Primary Production in Fish Ponds and its
Application to Fertilization Experiments. Limnol. Oceanogr., 7:
131-135.
(33) . 1962. Ten Years of Research in Fish Pond Fertili-
zation in Israel. I. The Effect of Fertilization on Fish Yields.
Bamidgeh, 14: 29-38.
(34) . 1963. Ten Years of Research in Fish Pond Fertili-
zation in Israel. II. Fertilizer Dose and Frequency of Fertili-
zation. Bamidgeh, 15: 78-92.
(35) .1968. Some Limiting Factors Affecting the Dose of
Fertilizers Added to Fish Ponds with Special Reference to the
Near East. Proc. World Symposium on Warm-water Pond Fish
Culture, FAO United Nations, Fish. Rep. No. 44, 3: 1-7.
(36) HICKLING, C. F. 1962. Fish Cultures. Faber and Faber, London.
295 pp.
(37) HORA, S. L. AND T. V. R. PILLAY. 1962. Handbook on Fish Culture
in the Indo-Pacific Region. FAO Fisheries Biology Technical
Paper No. 14. 204 pp.
(38) IRWIN, W. H. AND J. H. STEVENSON. 1951. Physiochemical Nature
of Clay Turbidity with Special Reference to Clarification and
Productivity of Impounded Waters. Okla. Agr. Mech. Coll. Bull.,
Arts and Sci. Studies, Biol. Ser., 48: 1-54.
(39) JHINGRAN, V. G. 1975. Fish and Fisheries of India. Hindustan
Publ. Corp., New Dehli, India. 954 pp.
(40) KESSLER, S. 1960. Eradication of Blue-Green Algae with Copper
Sulfate. Bamidgeh, 12: 17-19.
(41) LAWRENCE, J. M. 1954. A New Method of Applying Inorganic
Fertilizer to Farm Fish Ponds. Prog. Fish-Cult., 16: 176-178.
(42) LAY, B. A. 1971. Applications for Potassium Permanganate in
Fish Culture. Trans. Amer. Fish. Soc., 100: 813-815.
(43) LICHTKOPPLER, F. AND C. E. BOYD. 1977. Phosphorus Fertilization
of Sunfish Ponds. Trans. Amer. Fish. Soc., 106: 634-636.
(44) LOVELL, R. T. AND L. A. SACKEY. 1973. Absorption by Channel
Catfish of Earthy-Musty Flavor Compounds Synthesized by
Cultures of Blue-Green Algae. Trans. Amer. Fish Soc., 102:
774-777.
(45) MEYER, F. P., K. E. SNEED, AND P. T. ESCHMEYER (Editors). 1973.
Second Report to the Fish Farmers. Bur. Sport Fisheries and
Wildlife, Resources Pub. 113. Washington, D.C. 123 pp.
(46) MORRISON, F. B. 1961. Feeds and Feeding, Abridged. The Morri-
son Pub. Co., Clinton, Iowa. 696 pp.
(47) MORTIMER, C. H. 1954. Fertilizers in Fish Ponds. Her Majesty's
Stationery Office, Fish Pub. No. 5. London. 155 pp.
(48) PERRY, W. G., JR. AND J. W. AVAULT, JR. 1969. Experiments on the
Culture of Blue, Channel, and White Catfish in Brackish Water
Ponds. Proc. Ann. Conf. Southeastern Assoc. Game and Fish
Comm., 23: 592-605.
(49) PLUMB, J. A., J. M. GRIZZLE, AND J. DEFIGUEIREDO. 1976. Necrosis
and Bacterial Infection in Channel Catfish (Ictalurus punctatus)
following Hypoxia. J. Wildlife Diseases, 12: 247-253.
(50) RAPPAPORT, U., S. SARIG, AND Y. BEJERANO. 1977. Observations
on the Use of Organic Fertilizers in Intensive Fish Farming 
at the
Genosar Station in 1976. Bamidgeh, 29: 57-70.
25
(51) REE, W. R. 1965. Emergency Alum Treatment of Open Reser-
voirs. J. Amer. Water Works Assoc., 55: 275-289.
(52) ROBINETTE, H. R. 1976. Effect of Selected Sublethal Levels of
Ammonia on the Growth of Channel Catfish (Ictalurus puncta-
tus). Prog. Fish-Cult., 38: 26-29.
(53) ROMAIRE, R. P. AND C. E. BOYD. 1978. Predicting Nighttime
Oxygen Depletion in Catfish Ponds. Auburn Univ. (Ala.) Agr.
Exp. Sta., Bull. 505, 32 pp.
(54) )t , c. E. BOYD, AND W. J. COLLIS. 1978. Predicting
Nighttime Dissolved Oxygen Decline in Ponds Used for Tilapia
Culture. Trans. Amer. Fish. Soc., 107: 804-808.
(55) ROUSE, R. D. 1968. Soil Test Theory and Calibration for Cotton,
Corn, Soybeans, and Coastal Burmudagrass. Auburn Univ. (Ala.)
Agr. Exp. Sta., Bull. 375. 67 pp.
(56) SCHROEDER, G. L. 1974. Use of Fluid Cowshed Manure in Fish
Ponds. Bamidgeh, 26: 84-96.
(57) ._1975. Nighttime Material Balance for Oxygen
in Fish Ponds Receiving Organic Wastes. Bamidgeh, 27: 65-74.
(58) SMITH, E. V. AND H. S. SWINGLE. 1938. The Relationship Between
Plankton Production and Fish Production in Ponds. Trans. Amer.
Fish. Soc., 68: 309-315.
(59) . 1941. The Use of Fertilizer for
Controlling Several Submerged Aquatic Plants in Ponds. Trans.
Amer. Fish. Soc., 71: 94-101.
(60)_ . 1942. Organic Materials as
Fertilizers for Fish Ponds. Trans. Amer. Fish. Soc., 72: 97-102.
(61) SMITH, L. L., JR., D. M. OSEID, G. L. KIMBALL, AND S. M. EL-
KANDELGY. 1976. Toxicity of Hydrogen Sulfide to Various Life
History Stages of Bluegill (Lepomis macrochirus). Trans. Amer.
Fish. Soc., 105: 442-449.
(62) SWINGLE, H. S. 1947. Experiments on Pond Fertilization. A.P.I.
(Ala.) Agr. Exp. Sta., Bull. 264. 34 pp.
(63) .. 1961. Relationships of pH of Pond Waters to their
Suitability for Fish Culture. Proc. Pacific Sci. Congress 9 (1957),
Vol. 10, Fisheries. 72-75.
(64) 1968. Fish Kills Caused by Phytoplankton Blooms
and their Prevention. Proc. World Symposium on Warm-water
Pond Fish Culture, FAO United Nations, Fish. Rept. No. 44, 5:
407-411.
(65) . 1969. Methods of Analysis for Waters, Organic
Matter, and Pond Bottom Soils Used in Fisheries Research.
Auburn Univ., Auburn, Ala. 119 pp.
(66) AND E. V. SMITH. 1938. Fertilizers for Increasing
the Natural Food for Fish in Ponds. Trans. Amer. Fish. Soc., 68:
126-135.
(67) 1947. Management of Farm
Fish Ponds. API (Ala.) Agr. Exp. Sta., Bull. 254. 30 pp.
(68) THOMASTON, W. W. AND H. O. ZELLER. 1961. Results of a Six-Year
Investigation of Chemical Soil and Water Analysis and Lime
Treatment in Georgia Fish Ponds. Proc. Ann. Conf. Southeastern
Assoc. Game and Fish Comm., 15: 236-245.
(69) TISDALE, S. I. AND W. L. NELSON. 1956. Soil Fertility and Ferti-
lizers. MacMillan Co., N.Y. 430 pp.
(70) TOTH, S. J. AND D. N. RIEMER. 1968. Precise Chemical Control of
Algae in Ponds. J. Amer. Water Works Assoc., 60: 367-371.
(71) TRUSSELL, R. P. 1972. The Percent Un-ionized Ammonia in
Aqueous Ammonia Solutions at different pH Levels and Tem-
peratures. J. Fish. Res. Bd. Canada, 29: 1505-1507.
(72) TUCKER, C. S. AND C. E. BOYD. 1977. Relationships between
Potassium Permanganate Treatment and Water Quality. Trans.
Amer. Fish. Soc., 106: 481-488.
(73) 1978. Consequences of Periodic
Applications of Copper Sulfate and Simazine for Phytoplankton
Control in Catfish Ponds. Trans. Amer. Fish. Soc., 107: 316-320.
(74) WATERS, T. F. 1956. The Effects of Lime Application to Acid Bog
Lakes in Northern Michigan. Trans. Amer. Fish. Soc., 86:329-344.
(75) WOLT, J. D. AND F. ADAMS. 1978. Whatever Happened to Basic
Slag? Auburn Univ. (Ala.) Agr. Exp. Sta., Highlights of Agr.
Res., 25 (1): 15.
26
GLOSSARY
ACID. A substance characterized by the ability to react with bases or
alkali in water to form salts. An acid releases hydrogen ions upon
dissociation in water.
ACIDIC. Tending to be acid.
ACID DEATH POINT. A pH so low as to kill fish. A pH of less than 4
will usually kill fish.
ACUTE TOXICITY. The toxicity of a substance after a short exposure
time of a few hours or days.
AERATION. To aerate, to supply oxygen to pond water by mechanical
or physical means.
AGRICULTURAL GYPSUM. Calcium sulfate, CaSO
4
-2H20. This
compound may be used as a source of calcium or sulfur, but it is not a
liming material for use in fish culture.
AGRICULTURAL LIMESTONE. Calcium carbonate (CaCO
3
) or
dolomite (CaMg(CO3)2) which is finely ground and used to neutralize
acidity in soils, muds, and waters.
ALGICIDE. One of a group of plant poisons used to kill filamentous
algae and phytoplankton.
ALGAL SCUM. An undesirable visible layer of filamentous algae or
phytoplankton floating on the surface of a body of water.
ALKALINE. Relating to the hydroxide (OH-) or carbonate (C0
3
)
radical of a highly reactive group of metals that are characteristically
basic. Having a pH greater than 7.
ALKALINE DEATH POINT. Having a pH so great as to kill fish. A pH
greater than 11 will usually kill fish.
ALKALINITY. The total concentration of alkaline substances in water
expressed as milligrams per liter of equivalent calcium carbonate
(CaCO
3
).
AMMONIA. NH
3
, a colorless gas used in the manufacture of fertilizers.
It is also a form of nitrogen found in fresh water and may be toxic to fish
under certain conditions.
AMMONIUM HYDROXIDE. A solution of ammonia in water. It has the
formula NH
4
OH.
AMMONIUM ION. NH4, the positively charged ion resulting from the
reaction of ammonia in water. This ion is not appreciably toxic to fish.
ANALOGY. A relation of likeness between two things, consisting not in
the resemblance of the things themselves, but of two or more of their
attributes. The statement, "fish culture is agriculture," is an analogy.
AQUATIC ORGANISMS. Those plants and animals that live and grow
in the water.
AQUATIC WEEDS. Undesirable water plants growing in a pond. Any
plant growing in a body of water that reduces the ability of the water to
support fish life, or interferes with fishing or fish harvest.
ARID. Dry, lacking moisture. An area with low rainfall and high eva-
poration is an arid region.
BACTERIA. Single-celled microorganisms that lack chlorophyll.
Bacteria are important agents of decay and some species are responsible
for human, animal, and plant diseases.
BAFFLE. Any structure used to impede, regulate, or alter the flow or
direction of a liquid. For purposes of aeration, a baffle causes turbulence
in water flowing over it.
BASE. A chemical that has the ability to react with acids to form salts.
BASIC. Having a pH greater than 7, tending to form a base.
BASICITY. The degree of strength of a base.
BASIC SLAG. A liming material which is a by-product of the steel-
making industry, and is used to neutralize acidity of soils, muds, and
waters.
BENTHIC ORGANISMS. Organisms living in and on the mud of the
bottom of lakes or ponds.
BICARBONATE. Having HCO
3 
group, such as sodium bicarbonate
(NaHCO3).
BIOLOGIST. One who is trained in and studies biology, the science of
life.
BIOTA. Plant and animal life of a particular area considered as a total
ecological unit. For example, all of the organisms in a pond are
collectively termed the biota of the pond.
BIWEEKLY. Happening every 2 weeks.
BLUE-GREEN ALGAE. Any of the microscopic aquatic plants of the
division Cyanophyta. Blue-green algae are considered to be among the
simplest forms of plants.
BRACKISHWATER. Waters containing considerable salt but not as
much salt as the ocean; intermediate between fresh and salt water.
BUFFER. A substance capable of maintaining the relative concentration
of hydrogen (H') and hydroxide (OH ) ions in a solution by neutralizing,
within limits, added acids or bases.
BURNT LIME. Calcium oxide (CaO). This material is occasionally used
as a liming material.
CALCIUM CARBONATE. CaCO3, a white compound occurring
naturally as limestone rock. It is crushed and used in fish culture as a
liming material.
CALCIUM CARBONATE EQUIVALENT. The amount of calcium
carbonate required to be chemically equivalent to a given amount of
another substance. For example, 1 milligram per liter of hydrogen ion
has the same chemical reacting power as 50 milligrams per liter of
calcium carbonate.
CALCIUM HYDROXIDE. Ca(OH)
2
, also called hydrated lime or
slaked lime, a chemical compound which is sometimes used to lime fish
ponds.
CALCIUM MAGNESIUM CARBONATE. CaMg(CO
3
)
2
, a liming
agent used in fish culture. This is also called dolomite.
CALIBRATED ROPE. A line or rod that is marked at measured intervals
so that it may be used to determine distances.
CARBONATE. A substance having the CO
3 
group. For example,
CaCO
3 
is a carbonate of calcium.
CARBON DIOXIDE. An atmospheric gas. It is used by plants to
produce organic matter during photosynthesis and is released during
combustion, respiration, or organic decomposition.
CELSIUS. A temperature scale set up so that 0
0
C is equal to the freezing
point of water and 100
0
C is equal to the boiling point of water.
CENTIMETER. A unit of measurement equal to 1/100 meter or 0.3937
inch.
CLAY. Very fine soil particles. Grains of earth smaller than 0.002
millimeter are clay.
COAGULATE. To cause the transformation of dispersed particles in a
liquid into a semisolid or solid mass.
COLDWATER FISH. A fish which requires relatively cool water for
survival. The optimum temperatures of different species vary, but most
species are found in water where temperatures are usually 20
0
C or less.
Trout and salmon are coldwater species.
COMPLETE FERTILIZER. A fertilizer containing the primary
nutrients nitrogen (N), phosphorus (P), and potassium (K).
CONDUCTIVITY. The ability or power to convey electricity. In water,
the conductivity increases as a function of increasing concentrations of
ions.
COPPER SULFATE. A poisonous blue crystalline copper salt
(CuSO4"-5H
2
0) sometimes used in fish culture as an algicide or in
control of parasites and diseases.
CORRELATION. A simultaneous increase or decrease in value of two
related variables.
CRYSTAL. A symmetrical granular solid form of a substance.
DENITRIFICATION. To remove nitrogen from a material or chemical
compound. As an example, bacterial action in mud often converts nitrate
to nitrogen gas which is lost to the atmosphere.
DENSITY. The amount of a substance per unit volume. In physics, it
refers to the mass of a substance per unit volume; in limnology, plankton
density increases when the amount of plankton per unit volume of water
increases.
DETRITUS. Any disintegrated matter, such as organic debris,
accumulated in pond water or on mud or soil.
DIFFUSION. The movement of molecules of a substance from an area
of greater concentration to an area of lower concentration of the
substance. Diffusion will continue until equilibrium exists in the system.
For example, there is a net movement of dissolved oxygen molecules
from air into water until the pressure of oxygen molecules in the water
equals the pressure of oxygen molecules in the air.
DISSOLVED OXYGEN. The elemental oxygen gas contained in a body
of water and available for the support of fish life.
DIVALENT METAL ION. A metal atom that has lost electrons so that it
has a positive electrical charge of +2. These ions are capable of
combining with other ions of equal but opposite electrical charges to
form compounds, such as calcium ions combining with carbonate ions to
form calcium carbonate.
DRIFT. Carried along by wind or water currents.
EMULSIFIABLE CONCENTRATE. A liquid pesticide that will form a
suspension of small globules in water. The concentrated pesticide must
be diluted in water before application.
EPILIMNION. The upper layer of water in a pond or lake. Water of the
epilimnion is warmer than water in deeper layers.
27
EQUILIBRIUM. A stable balanced system. In chemistry, it is the state of
a reaction in which forward and reverse reactions occur at equal rates so
that the concentrations of the materials that are reacting do not change
with time.
EQUIVALENT. Equal in substance, degree, or value; having the same
ability to combine.
EVAPORATION. To convert or change into a vapor as when water
molecules diffuse into the air to become water vapor.
EVAPOTRANSPIRATION. The combined process of evaporation of
water and the loss of water from plants.
EXPONENTIALLY. Increasing by multiples of a number. The
dependent variable increases or decreases as a multiple (power) of the
independent variable.
FERTILE. Rich in nutrients needed to sustain plant growth.
FERTILIZATION. The act of increasing the fertility of the mud or
water in order to increase plant growth and, ultimately, fish production.
FERTILIZER. A natural or man-made material that is added to soil or
water to increase the production of desirable plants.
FERTILIZER FILLER. An inert material or limestone mixed with
fertilizer materials and used to bring the total ingredients of a complete
fertilizer up to a specified weight.
FILAMENTOUS ALGAE. Multicellular algae that grow in thin
threadlike sections.
FILTER ALUM. Aluminum sulfate (Al
2
(SO
4
)
3 
14H
2
0). This substance
coagulates particulate matter in water and is used to remove turbidity
from water.
FISH CULTURE. The deliberate growing and rearing of economically
important numbers of fish or other aquatic animals for recreational,
ornamental, scientific, or food purposes.
FLOC. A coagulated mass of particles.
FLOCCULATE. To cause particles to form lumps or masses.
FOOD WEB. A living ecological system in which plants are eaten by
small animals, which in turn are eaten by larger animals.
FRESHWATER. Inland waters, waters that contain little or no salt, 
not
salty or saline.
GOOD WATER QUALITY. Water having all the physical, chemical,
and biological characteristics necessary for the support and production
of an optimum amount of fish life.
GRANULE. A small, grain-like particle of a substance, often about the
size of sand grains.
GROUND WATER. Water from beneath the earth's surface that
supplies wells, springs, and dry-weather stream flow.
HARDNESS. Refers to the concentration of divalent metalic ions,
primarily calcium and magnesium, in the water expressed as calcium
carbonate equivalent.
HAVEN. A place of refuge.
HECTARE. A metric unit of area equal to 10,000 square meters or 2.471
acres.
HERBICIDE. A chemical used to control or destroy plants, especially
weeds.
HUMATES. Refers to partially decayed vegetable and organic matter.
HYDRATED LIME. Calcium hydroxide (Ca(OH)2), a liming material
occasionally used in fish culture.
HYDROGEN ION. The positively charged ion of hydrogen (H')
formed by the removal of the electron from atomic hydrogen.
HYDROGEN SULFIDE. A gas with the formula H
2
S. It is formed by
microbial decomposition of organic matter in the absence of oxygen.
Hydrogen sulfide is a weak acid in water and strongly dissociates into
HS and S at pH values above 7. Un-ionized H
2
S is highly toxic to fish.
HYDROLOGY. The study of the properties, distribution, and effects of
water on the earth's surface, in the soil and underlying rocks, and in the
atmosphere.
HYDROXIDE. A chemical compound containing the hydroxide ion,
OH-.
HYDROXIDE ION. The negatively charged ion OH characteristic of
hydroxides.
HYPOLIMNION. The lower layer of water near the pond bottom.
ILLUMINATED. Provided with light.
INERT. Exhibiting no chemical activity, totally unreactive.
IONS. An atom, group of atoms, or molecule that has acquired or is
regarded as having acquired a net electrical charge by gaining electrons
or by losing electrons from an initial electronically neutral state.
IONIZED. To become converted partially or totally into ions.
INORGANIC. Not composed of organic matter, involving neither
organic life nor the products of organic life.
INORGANIC FERTILIZER. Natural or man-made substances lacking
carbon composition, used to increase the ability of soil or water to
produce plant life.
KILOGRAM. One thousand grams, a metric unit of weight equal to 2.2
pounds.
LEACHED. To be dissolved and washed out by a percolating liquid.
LEEWARD. Located on or moving to the side toward which the wind is
blowing.
LIME. Refers specifically to calcium oxide. However, it is more
generally used to refer to any material used for raising mud pH and
alkalinity in fish culture or raising soil pH in agriculture.
LIMING. Applying neutralizing agents, such as agricultural limestone,
basic slag, hydrated lime, or burnt lime, to soil or water for the purpose
of increasing its basicity.
LINEARLY. Refers to dependent and independent variables. Each
successive unit of increase in the independent variable will cause the
same amount of increase or decrease in the dependent variable. When
plotted on ordinary graph paper, a relationship between the variable is
given as a straight line with a constant slope.
LITER. A metric unit of volume equal to 1,000 milliliters or 1.056 quarts.
MACROPHYTE. Relatively large vascular plants as opposed to the
microscopic phytoplankton, and filamentous algae. The basic structure
of an aquatic macrophyte is visible to the naked eye.
MANAGEMENT TECHNIQUES. With respect to fish and water
quality, it is the means by which a fish culturist can exert control and
influence over the water quality and, ultimately, the fish production of a
pond.
MANURE. Animal dung, compost, or other organic matter used as
fertilizer. The nutrients are released from the manure as it decays. The
decay of manure in water is caused by bacterial action and requires
dissolved oxygen.
METABOLIC WASTE. By-products of metabolism excreted from the
body of an organism.
METABOLISM. The complex and chemical processes involved in the
maintenance of life.
MICROGRAM. Metric unit of measure equal to 1/1,000,000 gram.
MICROSCOPIC. Too small to be seen by the unaided eye.
MILLIGRAM. Metric unit of measure equal to 1/1000 gram.
MILLIMETER. A metric unit of measure equal to 1/1000 meter or
0.0394 inch.
MILLIGRAM PER LITER. One milligram of a substance in 1 liter of a
second substance. It is a way of expressing concentrations of small
amounts of a substance dissolved in another substance.
MORPHOMETRY. The structure, form, or shape of an object, thing,
body of water, or place.
NEUTRALIZE. To make a solution chemically neutral as when an acid
and a base react to form a salt and water.
NITRATE. The nitrate ion has the formula NO
3
. Substances containing
the NO
3 
group are termed nitrates.
NITRITE. The nitrite ion has the formula NO
2
. Substances containing
the NO
2 
group are termed nitrites.
NITRIFIED. To oxidize reduced nitrogen forms to nitrate. The action
of certain bacteria will convert ammonium (NH4) to nitrate. The
ammonium is said to be nitrified.
NUTRIENT. Something that provides life sustaining nourishment, an
element necessary for life and growth.
OFF-FLAVOR. Bad tasting, varying from the usual flavor.
OPTIMUM. Most favorable or advantageous. The best conditions or
degree or amount for a particular situation.
ORGANIC MATTER. A living substance or its remains. Organic matter
contains carbon.
ORGANIC FERTILIZER. Materials derived from animal waste
products or dead animals or plants which are used to supply nutrients to
soil and water to increase plant growth.
OSMOTIC PRESSURE. The pressure exerted by the tendency of fluids
to diffuse through a semi-permeable membrane until there is an equal
concentration of fluid on either side of the membrane.
OXIDIZE. To combine with oxygen, to make into an oxide.
OXYGEN DEMAND. The oxygen required by all the biological and
chemical processes that occur within a pond.
PARTS PER 'MILLION. A means of expressing concentration, usually
by weight, as one portion of a substance in 999,999 portions of a second
substance; e.g. 1 pound of lime in 999,999 pounds of water. 1 part per
million - 1 milligram per liter.
28
PARTICULATE ORGANIC MATTER. Particles of living or dead
organic matter which are suspended in water. Plankton is a form of
particulate organic matter.
PESTICIDE. Any chemical used to control or kill harmful or unwanted
plants or animals.
PHENOLPHTHALEIN ALKALINITY. The equivalent amount of acid
required to lower the pH of a water sample of 8.3 (the endpoint of the
indicator phenolphthalein), expressed as milligrams per liter of
equivalent calcium carbonate.
PHOTOSYNTHESIS. The process by which green plants convert light
energy into chemical energy and make organic compounds from
inorganic compounds, especially carbohydrates from carbon dioxide
and water, with the release of oxygen. Photosynthesis may be thought of
as the production of food by a plant.
PHYTOPLANKTON. Microscopic aquatic plants which are suspended
in water. They are usually the major oxygen producing organisms in a
pond.
PHYTOPLANKTON DIE-OFF. An abrupt, massive mortality of
phytoplankton resulting from natural or man-made causes.
PLANKTON. Plant and animal organisms, generally microscopic, that
are suspended in natural waters.
PLANKTON BLOOM. A large quantity of plankton giving water a
definite color. Pond water usually appears green because the majority of
plankton organisms are greenish, but plankton blooms may also appear
black, yellow, red, brown, or blue-green.
PLANKTONIC. Of or relating to plankton.
POOR WATER QUALITY. Water having some physical, chemical, or
biological characteristic such that the support and production of fish life
is less than the optimum.
PRECIPITATE. To chemically cause a solid substance to be separated
from a solution.
PRECIPITATION. Any form of rain or snow. Water droplets or ice
particles condensed from the atmospheric water vapor and sufficiently
massive to fall to the earth's surface.
PRIMARY NUTRIENTS. Referring to the fertilizer elements nitrogen
(N), phosphorus (P), and potassium (K). An increase in plant growth
most often follows the application of these essential nutrients to the
water or soil.
QUADRANT. A circular arc of 90 degrees, one-quarter of the
circumference of a circle.
REAGENT. Any substance used in a chemical reaction to detect,
measure, examine, or produce other substances.
RESIDUAL EFFECT. The length of time in which the effect of a
treatment of an ecological system with a chemical will persist.
RESIDUAL TOXICITY. The continuing toxicity of a substance applied
to an ecological system.
RESPIRATION. The metabolic process by which an organism
combines oxygen with organic matter and releases energy, carbon
dioxide, and other products of oxidation. Respiration can be thought of
as the utilization of food by a plant or animal.
ROTENONE. An organic compound extracted from the roots of derris,
timbo, and cube' and used as an insecticide and fish poison.
RUNOFF. Rainfall that is not absorbed by the soil and flows over the
land surface of the earth.
SALINITY. Relating to the concentration of mineral salts in the water.
SALT. Any chemical compound that is formed by replacing all or part
of the hydrogen ions of an acid with one or more positively charged ions
of a base. Sodium chloride (NaC1) is a common salt.
SATURATED. To contain all of a substance that can normally be
dissolved in a second substance at a given temperature and pressure.
SEA WATER. Salt water of the oceans.
SECCHI DISK. A disk 20 centimeters in diameter painted in alternate
quadrants black and white and used in fish culture and limnology to
measure the passage of light through the water.
SEINE. A large fish net made to hang vertically in the water with floats at
the top and weights on the bottom and a staff attached to each end; to
catch fish with such a net.
SILT. A soil material consisting of fine mineral particles intermediate in
size between sand and clay. Silt is suspended in runoff, but when runoff
enters a pond, the silt settles to the pond bottom.
SMOTHER. To deprive of oxygen, to conceal, suppress, or cover.
SOLUBILITY. The amount of a substance that can be dissolved in
another substance.
SOLUTION. A uniformly similar mixture of one or more substances that
will not settle out. Sodium chloride added to water dissolves to form a
solution of sodium chloride.
SOUNDINGS. To measure the depth of a body of water with a
calibrated line or rope.
SOURCE MATERIALS. Original materials from which essential
fertilizer nutrients are derived. Phosphate rock is the source material for
elemental phosphorus.
STRATIFY. To become layered, as when a warm layer of water overlies
a cooler layer of water.
STRESS. To subject an organism to physically disruptive forces that are
harmful to that organism's growth and survival.
SUBLETHAL. Not causing death. A sublethal concentration of a
substance will not cause death, but may cause stress or injury.
SULFIDE. A chemical compound containing bivalent sulfur.
SUPERSATURATED. To cause a chemical solution to be more highly
concentrated than is normally possible under given conditions of
temperature and pressure.
SUSPENSION. A relatively coarse dispersion of solid particles in a
liquid. For example, silt in water is a suspension.
TEMPERATE REGION. Neither very hot nor very cold in climate.
THERMAL STRATIFICATION. The separation of pond waters into
distinct warm and cool layers caused by differential heating or cooling of
such waters.
THERMOCLINE. The layer of water between the epilimnion and the
hypolimnion; the layer where there is a great change in temperature per
unit of depth.
TITRATING AGENT. A chemical substance used to determine the
concentration of another chemical substance in a solution.
TOLERATE. To endure or resist, to bear, to survive.
TOPOGRAPHIC. The physical features of a region or place.
TOTAL ALKALINITY. The total measurable bases (OH HCO
3
,
COa) in the water. The total alkalinity of a water is a measure of its
capacity to neutralize acids.
TOTAL DISSOLVED SOLIDS. The total concentration of all
substances in true solution in water.
TOTAL HARDNESS. The total amount of divalent metallic ions in the
water, expressed as milligrams per liter of equivalent CaCO3. The
principal hardness causing ions are calcium and magnesium.
TOXICITY. The degree of being harmful, destructive, or poisonous to
life.
TRACE NUTRIENTS. Nutrient elements essential for the life and
growth of an organism, but needed in only very small quantities or
amounts.
TRANSECTS. To divide by cutting crosswise. In sampling, a transect is
an imaginary or real line along which samples are taken.
TRANSPIRATION. The giving off of water vapor from plant pores as a
part of plant metabolism.
TROPICAL REGION. Hot and humid in climate. Near the equator.
TURBIDITY. Having sediment (soil) or foreign particles (plankton)
suspended in the water.
TURBIDITY UNIT. A unit of measurement for describing the amount
of turbidity in the water.
UNBALANCED FISH POPULATION. Refers to a population of sport
fishes which produces few fish of large enough size to be considered
harvestable. A sport fish population which produces poor fishing.
UN-IONIZED. Not ionized, elemental, not electrically charged.
UN-IONIZED AMMONIA. This form of nitrogen has the formula NH
3
.
Un-ionized ammonia is toxic to fish.
VARIABLE. A characteristic subject to change, having no fixed
quantitative value.
WARMWATER POND FISH. Fish that normally survive, grow, and
reproduce in warm water (250 to 32
0
C).
WATER ANALYSIS. A determination of the quantities or amounts of
certain water quality variables in a body of water.
WATER QUALITY. All the physical, chemical, and biological factors
which influence the beneficial use of water.
WATER QUALITY VARIABLE. Any changeable characteristic of
water which affects the survival, growth, production, or management of
fish.
WATERSHED. The land area draining into a river system or body of
water.
WETTABLE POWDER. A finely ground solid pesticide that can be
mixed with water before application and use.
ZOOPLANKTON. Microscopic aquatic animals which are suspended in
water.
29
METRIC AND ENGLISH
Length
Metric
1 millimeter
1 centimeter
1 meter
Weight
1 milligram
1 gram (1,000 milligrams)
1 kilogram (1,000 grams)
Area
1 square meter
1 hectare (10,000 square meters)
Volume
1 milliliter
1 liter (1,000 milliliters)
3.785 liters
Other
1 kilogram per hectare
1 milligram per liter
1 milligram per kilogram
o
C
0
1
2
3
4
5
6
7
8
9
10
11
12
13
EQUIVALENTS
English
0.0394 inch
0.3937 inch
3.281 feet
0.00035 ounce
0.0353 ounce
2.205 pounds
10.76 square feet
2.471 acres
0.0338 U.S. liquid ounce
1.057 U.S. liquid quarts
1.00 U.S. liquid gallon
0.892 pound per acre
1 part per million
1 part per million
CELSIUS TO FAHRENHEIT DEGREES
o
F  
oC o
F  
o
C
32.0 14 57.2 28
33.8 15 59.0 29
35.6 16 60.8 30
37.4 17 62.6 31
39.2 18 64.4 32
41.0 19 66.2 33
42.8 20 68.0 34
44.6 21 69.8 35
46.4 22 71.6 36
48.2 23 73.4 37
50.0 24 75.2 38
51.8 25 77.0 39
53.6 26 78.8 40
55.4 27 80.6
CHEMICAL SYMBOLS OF SELECTED ELEMENTS
Element Symbol
Aluminum ................. ........................... Al
Arsenic ..... .......................................... As
B oron ....... ................................................ B
Carbon ...................... ........................... C
Calcium ....... ............................................. C a
Chlorine................. i .............................. Cl
Copper..................... ........................... Cu
Iron...................... ............................ Fe
Hydrogen.................... ........................... H
Mercury ................... ........................... Hg
Potassium................... ............................ K
Magnesium ................. .......................... Mn
Manganese................. ........................... Mn
Nitrogen.................... ............................ N
Sodium..................... .......................... Na
Oxygen..................... ........................... O
Phosphorus ................. ............................ P
Sulfur ............................................ .......... S
Silicon..................... ........................... Si
Zinc..................... ............................. Zn
o
F
82.4
84.2
86.0
87.8
89.6
91.4
93.2
95.0
96.8
98.6
100.4
102.2
104.0
30