Suggested
Management
to Improve
Quality
and Reduce
Quantity of
-Channel 
Catfish
Pond Effluents
Niwi xii. F. S 11W \k I I AND) 0i U1)u [. Bo~ i)
R ECENT INTEREST IN REGIJLAI ING aqu~acLltute_ effIluents 
has
caulsed tesearcherS to 'OCLIS on1 Char-aCte-i/in 111pondC eff'LIlucts 
and de\cdoping
techiqueLIs to redceIIC x ol nine anid i mp oxe qual ity ol thCSeci 1.1 ucut1s. 
Analy ses olf
wxaters I romi conmmercial channel cattish ponds itulicatcd that Concentr 
at ions of,
I)IClta 11 P1Iutanlts suIch as planlt nuLtlnenltS. 01'Lcan iC maItter,. and Solids xxI- 
Icrc h eher
thanl those I ou~nd inl t\ pical receix in-I streams. Ui i lss ponds sti 
atiflied, there \\ as
little dill erenclce inl Concentrations ol1 potential p)olutants betxxC~ eusurtacC 
anld
bottom wxaters. Aetrat ion is an cii ct ix technliqueI 1I- 
r prex ent i thermIlal anld
chemical stratificattin. T he xxater i ill 1OSt Cattish pond1Cs is t1101toti1h 
IN mixed by
aeratioll. so tile Composition (ot thi liluet Telshoul11d closeix' I Ceemble 
that ol
pond sul ace xxaters. Studies 0t1 the quLal itx (1' cit Iluilts dut~gl 
pond drainii-IL0
xvenilied tilat this concIlusionl "xas t1ie I or -tle iilitiail 80-90% ol cit luetlt. 
buttie last
10) 20'( 0i'tile eluenC~t xxas mu1Lch 1note- C0ilCciltrated bcausLIi 
ti'e StispenISiOn o1'
solids 11N bottom soil disturbance llx Isil and seiiliilc( aIctixities. 
Dui)Lilc~ drIajillileI-.
5W4 Ott( (IIti[l etial po01l tailtS discharged itrom a poind ate di scharged 
inl tile last
10-20(( of tile \\ ater.
Schw art, is a g radunate research assistant an BlIoy d is a p~rofesor in the D epa rtmient 
of F'isheries
andi kIIiv(I k (luiacuitures.
Preparation ot this repo(rt %% as funided in cooperation %%ith t he klaiaiana D~epa rtmient 
oil' m ironnientat
M anagement andi the t nited States F.ii i ronniei ta I Protect ion \ penc \i it h Cliean \%ater 
\et Sect ion
319 IDenionsl ration Funds1(.
LEAFLET 108 MARC 1996
ALABAMA AGRICULTURAL EXPERIMENT STATION AUBURN UNIVERSITY, 
ALABAMA
LOWELL T FROBISH, DIRECTOR
2 Suggested Management to Improve Quality and
One method of reducing the amount of effluents from ponds is to operate
them without draining, which is a common practice of catfish farmers in
Mississippi. Research conducted at the Auburn University Fisheries Research Unit
of the Alabama Agricultural Experiment Station System revealed that, over a three-
year period, it was possible to maintain adequate water quality for good fish
production in undrained ponds harvested each year by seining. After several years,
catfish ponds must be drained to repair levees and for fish inventory adjustment.
When it is necessary to drain ponds, the last 10-20% of water in the pond can be
held for two or three days to significantly reduce amounts of pollutants through
sedimentation.
Pond bottom soils contribute to the pollution potential of catfish ponds.
Aeration, water circulation, and pond bottom treatments may be used to enhance
decomposition of organic matter in pond soils. Striving to improve sediment and
water quality and reduce the volume of effluents can produce numerous positive
side effects: environmental conditions in ponds can be enhanced, more efficient
fish production can be achieved, and less water will be used.
A constructed wetland, tested in Hale County, was very efficient in
removing potential pollutants from pond water providing that at least a two-day
hydraulic retention time (HRT) was used. However, since this process requires a
large amount of land, wetlands should be used for treating only a portion of the
waste from catfish ponds. A 2.5-acre wetland would be required to treat all the
effluents from a 2.5-acre pond with an average depth of 4.5 feet. Taking into
account the two-day HRT, this process would last one week. Treating only the
most concentrated effluents in the final stages of draining would minimize the
amount of land needed for constructed wetlands, and significantly improve the
quality of these effluents.
Research results show that catfish farmers could use the following
suggestions to develop inexpensive techniques for reducing the pollution potential
and volume of pond effluents:
(I) Use high quality feeds and conservative management practices.
High quality feeds improve feed conversion ratios and reduce quantities
of metabolic waste and uneaten feed. Conservative feeding practices and lower
stocking rates reduce feed inputs and improve feed conversion ratios. Feeds are
the ultimate source of pollutants in catfish pond effluents. The main types of
wastes in aquaculture are residual food, fecal matter, and metabolic by-products.
Because feed is about 90% dry matter and fish are only about 25% dry matter,
only 18% of feed dry matter will be recovered as fish dry matter at a good feed
conversion ratio of 1.5. The remainder of the dry matter stays within the pond
system to affect its water quality. Inefficient feed conversion results in poorer
quality effluents because the feed not converted into fish flesh enters the pond as
waste.
(2) Aerate and circulate pond water.
Maintenance of dissolved oxygen concentrations above four or five parts
Reduce Quantity of Channel Catfish Pond Effluents 3
per million enhances the appetite of fish and encourages good feed conversion
ratios. Circulation prevents stratification and enhances degradation of organic
matter in pond bottoms. An evenly oxygenated pond will oxidize organic matter
rapidly. Oxidation of organic matter within the pond diminishes the amount of
organic matter in effluents.
(3) Minimize water exchange.
Water exchange can be used to reduce high concentrations of ammonia
or other toxic substances if large volumes of pond water are exchanged at once.
The displaced pond water represents a pollution load in receiving waters, and
heavy water exchange should not be used unless absolutely necessary. Routine
water exchange has little effect on water quality and should not be employed.
(4) Harvest fish without draining ponds or drain ponds in winter
or early spring.
Many farmers use this practice already, and both research findings and
experience suggest that water quality is not greatly impaired by continuous
production. Ponds have to be drained every few years for repairs and fish inventory
adjustment. When ponds must be drained, do so in winter or early spring when
there is little or no feed input. Pond water quality normally is better in cool months
than in warm months, and greater stream flow in cool months provides 
more
dilution of pond effluents.
(5) Treat pond bottoms.
Reducing the amount of organic matter entering ponds through 
use of
high quality feeds, more efficient feeding practices, and lower stocking rates
improves the condition of pond sediments. Old ponds that have accumulations of
organic matter in bottom soils can be rejuvenated after draining for harvest. Pond
bottoms can be dried for several weeks and tilled to a depth of four to six inches
to provide better contact of soil with air to accelerate organic matter 
decomposition.
Acidic soils in pond bottoms should be treated with agricultural limestone to
increase pH and enhance microbial activity.
Application of hydrated lime or quick lime to pond bottoms enhances
ammonia volatilization and kills pathogenic organisms. However, both hydrated
lime and quick lime will raise the pH so high that microbial 
activity will be
temporarily inhibited.
(6) Reuse water.
Fish harvest is facilitated by lowering the water level in ponds to 10-
20% of the full pond volume. Instead of draining ponds for fish harvest, 
water
can be pumped to adjacent ponds and then reused in the same or other ponds.
Production ponds can be built with higher levees or water levels maintained with
more free board to provide storage volume. Water from one pond can be transferred
to another with a low-lift pump and then transferred back by siphon.
(7) Minimize water discharge.
Maintain the water level in ponds several inches below the level of the
drain pipe to collect surface runoff and rainfall without allowing the pond to
overflow. This method will also help to conserve water. Watershed 
ponds'should
not have watershed areas larger than necessary 
to keep ponds full,:because
excessively large watersheds increase runoff into 
ponds and result in high
discharge. Runoff from watersheds may be partially diverted 
from ponds by
terracing or other means.
(8) Use ponds as settling basins.
Minimize seining activity during harvest to avoid stirring up 
sediments.
After seining, hold the water in the pond for two to three 
days to allow solids to
settle before draining completely. An even better method 
is to not discharge this
last portion of water. Holding water for two days after seining reduced 
the discharge
of settleable solids by 96%, total nitrogen by 74%, total 
phosphorus by 69%, and
organic matter by 59%.
(9) Use constructed wetlands.
A wetland can be created by constructing a two-foot-high 
dike around
the area in which the water will be impounded. A minimal 
slope is provided in
order to insure water flow from one end to the other. 
The shape of the wetland
should be rectangular with an aspect ratio of anywhere 
from 5-10:1. Because
wetlands function best with emergent, reed swamp plants 
such as bulrushes and
cattails, the maximum depth for a wetland should 
be about 18 inches. Common
cattails and bulrushes can be gathered from the wild 
and planted in wetlands. The
wetland should be large enough to provide a two- to 
four-day retention time for
in-flowing water. Wetlands should be down slope 
from ponds, so water can flow
by gravity from ponds into the wetland. The 
USDA Soil Conservation Service
can provide advice on designing and constructing 
wetlands.
To illustrate how wetlands could be integrated 
into pond management,
pond water levels could be lowered for fish harvest 
by pumping 80-90% of the
water to adjacent ponds for storage, and the remaining 
water, which is highly
concentrated with wastes, could be discharged 
through a constructed wetland. A
wetland centrally located on a farm, or connected to an 
integrated drainage system
would save on construction costs and use land efficiently. 
Such a system would
also allow a wetland to be used to treat the overflow 
coming from ponds after
rainfall. Pond drainings could be staged in time so that 
only one pond is being
drained at a time; this will allow the use of only one 
wetland to treat the effluents
from numerous ponds and will also allow 
water from a draining pond to be
transferred to another drained pond so that only 
the effluents from one pond might
need to be released into the environment and the 
rest could be conserved. Effluent
from a constructed wetland could even be re-used 
if needed.
Information contained herein is available to all persons without regard
to race color sex, or national origin