utrient inputs into pond water and is
an important aspect of water quality
management in catfish farming.
Explanation
Fish do not convert all of the applied feed to
flesh. Fish harvested from ponds usually
contain about 7.5 to 15% of organic matter,
20 to 30% of nitrogen, and 25 to 35% of
phosphorous applied to ponds in feed. The
difference in the input of a substance in feed and
the amount of this substance in harvested fish
represents the amount of the substance that
enters the pond ecosystem as uneaten feed and
in fish feces and metabolites. Uneaten feed and
feces are decomposed to metabolites by pond
bacteria. The metabolites of most interest are
carbon dioxide, ammonia, and phosphate,
because these substances are basic nutrients
for production of phytoplankton. They also
represent potential pollutants in pond effluent.
Nutrient inputs and phytoplankton abundance in
ponds increase as feeding rates increase.
Mechanical aeration is used to maintain
adequate dissolved oxygen concentrations and
to favor oxidation of ammonia to nitrate by
nitrifying bacteria. However, if feeding rates
exceed 100 to 120 lb/acre per day, water quality
in ponds tends to deteriorate unless mechanical
aeration is increased substantially. Deterioration
of water quality in ponds stresses fish and
causes them to eat less, grow slowly, and to be
more susceptible to disease. Moreover,
effluents from ponds with lowered water quality
have an increased pollution potential.
Feeds and management
Practices
· Select high quality feeds that contain
adequate, but not excessive, nitrogen and
phosphorous.
· Store feed in well-ventilated, dry bins, or if
bagged, in a well ventilated, dry room. The
feed should be used on a first in and first out
basis by the expiration date suggested by
the manufacturer.
· Apply feed uniformly with a mechanical
feeder.
· Do not apply more feed than fish will eat.
· Maintain adequate dissolved oxygen
concentrations in ponds to prevent fish
stress and enhance the capacity of the pond
to assimilate metabolic wastes.
· Daily feed application should not exceed
30 lb/acre in un-aerated ponds. In ponds
with 2 hp of aeration per acre, daily feed
application usually can be increased to
Auburn University and USDA/Natural
Resources Conservation Service
Alabama Aquaculture
Best Management Practice (BMP)
Feed
Management
BMP No. 7 100 to 120 lb/acre. These feed amounts are
the maximum amounts to be applied on a
given day. They are not annual averages.
Implementation notes
Because feed is the main source of nutrients in
ponds, good feed management, reasonable
stocking and feeding rates, and adequate
mechanical aeration is the best way to enhance
effluent quality. Use of high quality feed that has
no more nitrogen and phosphorous than
necessary is important. Reasonable
percentages of these elements in feeds for
grow-out are 4.5 to 5.1% (28 to 32% crude
protein) for nitrogen and 0.75 to 1.0%
phosphorous. Somewhat higher percentages
may be necessary in feeds for fry or fingerlings.
Proper attention to feed storage to prevent
excessive heat and moisture and care to always
use fresh feed protects feed quality and
improves the efficiency with which fish can use
it.
Mechanical feeders that spread the feed
uniformly around the edges of ponds assure that
all fish have an opportunity to eat an adequate
amount of feed. This procedure also allows the
manager to better observe feeding activity.
Overfeeding is wasteful, costly, and results in
unnecessary feed and nutrient inputs to ponds.
Although feed consumption depends largely on
the weight of fish in a pond, other factors are
important in controlling feed consumption. Fish
will not eat as well when water temperature is
too low or too high. Poor environmental
conditions such as low dissolved oxygen
concentration and high ammonia concentration
or high pH stress fish and depress their appetite
as well as their ability to convert consumed food
into growth. Disease and parasite problems
also will lead to decreased feed consumption by
fish. Thus, managers must observe conditions
in ponds and the feeding behavior of fish to
prevent overfeeding. A sure sign of overfeeding
is the accumulation of feed in corners of ponds.
Moderate stocking and feeding rates and
adequate mechanical aeration are necessary for
assuring good water quality. Mechanical
aeration prevents low dissolved oxygen
concentrations and fish stress can be avoided.
Aeration also improves the effectiveness of the
pond ecosystem to assimilate wastes from
feeding, and effluents from properly aerated
ponds will not have low dissolved oxygen
concentrations.
Dissolved oxygen concentration should be
monitored at night, and frequent excursions of
dissolved oxygen concentration below 3 or
4 mg/L suggest excessive feeding and less than
adequate aeration (See BMP No. 9).
Underwater visibility in ponds should not be less
than 12 inches even where dissolved oxygen
concentrations are adequate. Underwater
visibility can be measured best with a Secchi
disk (Figure 1). This disk is lowered into the
water by a calibrated line until it just disappears.
The depth at which the disk disappears is called
the Secchi disk visibility. Ponds with excessively
dense phytoplankton blooms may have high
ammonia concentrations and other water quality
problems.
Figure 1. Secchi Disk.
Comment
The feed conversion ratio (FCR) is the weight of
feed applied divided by the weight of fish
produced. This ratio is very important in pond
aquaculture because it indicates the efficiency of
feed use. In catfish culture, FCR values on
different farms often range from 1.5 to 2.5. A
value of 2 is usually considered acceptable, but
farmers should strive to reduce the FCR to
1.8 or less. A better FCR will make catfish
production more efficient. It will protect effluent
quality because nutrient inputs per unit of fish
production decline as FCR improves. References
Boyd, C. E. and C. S. Tucker. 1998. Pond
Aquaculture Water Quality Management.
Kluwer Academic Publishers, Boston, MA.
Gross, A., C. E. Boyd, and R. T. Lovell. 1998.
Phosphorus budgets for channel catfish
ponds receiving diets with different
phosphorus concentrations. Journal of the
World Aquaculture Society 29:31-39.
Lovell, R. T. 1988. Nutrition and Feeding of
Fish. Van Nostrand Reinhold, New York,
New York.


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