WATER QUALITY CONTROLE IN CATFISH FARMING IN NIGERIA

Water Quality Management Monitoring and managing water
quality is essential for successfully
producing a crop of fish. Dissolved
oxygen, nitrite, ammonia, pH and
other factors affect the
environmental quality of the production pond. Failure to
maintain good water quality will at
best result in poor performance
and at worst result in the loss of an
entire crop of fish. Dissolved Oxygen In many cases, lack of sufficient
dissolved oxygen limits the success
of a crop. Oxygen is necessary for
survival of most plants and
animals. In the atmosphere,
oxygen concentrations are relatively constant at a given
altitude. At sea level, the
atmosphere is 21-23% oxygen. In
water, oxygen concentrations
fluctuate daily. The amount of
oxygen water holds depends primarily on temperature. The
warmer the water, the less oxygen
it can hold. Also, the greater the
altitude, the less oxygen water can
hold. Oxygen depletion in a pond results
when demand exceeds supply.
Aquatic animals, plants and
decaying organic matter consume
oxygen. Aquatic plants are primary
producers of oxygen. Plants produce oxygen as a by-product of
photosynthesis, and the rate of
photosynthesis depends on the
amount of light. This is why the
amount of oxygen in pond water
fluctuates daily. Oxygen levels are usually highest
at mid-afternoon and lowest just
before sunrise. Fish kills usually
occur when more oxygen is
consumed during the night hours
than is produced during daylight hours. Warm water does not
contain as much oxygen as cold
water. Thus, during warm weather
months, mismanagement of ponds
by overstocking, overfeeding,
overfertilization, pollution from barns and feedlots or chemical
treatment of aquatic weeds can
result in oxygen depletion and fish
kills. Several calm, cloudy days
during warm weather can also
result in oxygen depletion and fish kills. Producers should be alert to the
possibility of oxygen depletion: 1. after a heavy rain 2. during periods of strong winds 3. during periods of calm, cloudy
days 4. during the fall when air
temperatures are rapidly cooling 5. after chemical treatment of aquatic
weeds 6. if the water color changes suddenly If one or more of these conditions
exist, inspect ponds several times
daily for signs of oxygen depletion. Signs of oxygen depletion include: Large numbers of fish swim to the
top and gulp air at night or early in
the morning. If disturbed, they
dive but quickly return to the
surface. If oxygen depletion has not
reached a lethal level, fish are at
the surface in the early morning
but return to deeper water as
oxygen builds during the day. This
may continue for several days. The producer should take corrective
action immediately. Feeding habits suddenly change. Measuring the oxygen level in a
pond is the only reliable way to
detect a developing problem.
Oxygen test kits and meters are
available. Test the pond at dusk or
after dark and then again at dawn or shortly thereafter.If oxygen is
less than 3 parts per million (ppm)
in the top 3 feet of water or the
pond shows signs of oxygen
depletion, immediate action should
be taken to prevent fish losses and reduce stress.

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