HOW TO CONTROL WATER QUALITY IN FISH FARMING IN NIGERIA

Emergency Aeration The most effective emergency
treatment is mechanical aeration of
the water (Figure 3). Whichever
method is used, the sooner it is
applied and the larger the volume
of water sprayed or agitated per unit time and the sooner a current
is established, the more effective
the method will be. It is important
not to disturb the bottom. Bottom
muck contains organic material
and decomposing bacteria that will contribute to oxygen depletion
problems if mixed with water. Paddle Wheel Aerator There are various designs for
paddle wheel aerators. Plans are
available for a homemade model
using a car or truck differential
mounted on a trailer frame, with a
paddle wheel on each end of the differential and a power take-off
attached. Commercial units are also
available. These aerators have
performance data and
maintenance/service assistance
from the manufacturer. Large Volume Pumps Various large volume water pumps
can be used to aerate a pond.
Ideally, the pump should be set up
so that it creates a current and at
the same time blows or sprays
water across the pond surface. Water Replacement Water replacement is also very
effective. Unfortunately, some
ponds do not have an alternative
water source with enough volume
to be effective. Supplemental Aeration Several devices on the market are
designed to provide supplemental
aeration. Supplemental methods
prevent oxygen depletion, while
emergency methods correct
oxygen depletion once it has occurred. Although emergency
methods are effective, they are
usually too difficult and expensive
to use continuously. For a commercial fish farmer, the
use of supplemental aeration can
improve water quality and
production and decrease losses.
This is especially true if adequate
amounts of water are not available to flush the pond periodically
during the hot summer months. pH Fish can live in waters having a pH
range from about 5 to 10. The
desirable pH range for fish
production is 6.5 to 9.0. The pH of
pond water is influenced by the
amount of carbon dioxide present. Much of the carbon dioxide (CO2) in water is the result of animal and
plant respiration. Carbon dioxide is
used in photosynthesis. Therefore,
carbon dioxide concentrations in
water increase at night and
decrease during daylight hours. Since carbon dioxide is acidic, the
pH of water is usually highest in
the late afternoon and lowest just
before sunrise. The extent of daily fluctuations in
pH is affected by the buffering
capacity of water. Bicarbonates are
important buffers in pond water. In
some areas, ponds and lakes have
soft water and are slightly acidic. They are generally low in
bicarbonate buffers. Adding
agricultural lime (CaCO3) to a pond increases the bicarbonate buffering
capacity of the water. This can
increase morning pH, lower
afternoon pH values and reduce
daily changes in pH. Alkalinity and Total Hardness Alkalinity is a measure of the total
concentration of bases in water
expressed as mg/liter (ppm)
equivalent to calcium carbonate.
Alkalinity is a measure of the
bicarbonate-carbonate buffering system described in the section on
pH. Alkalinity is a more reliable
indicator of lime requirements
than water hardness. However,
alkalinity is more difficult to
measure and is subject to change during the interval between
sampling and analysis in the
laboratory. Accurate
measurements can be made at the
pond site with a test kit. Carbon Dioxide High CO2 levels can be a problem associated with oxygen depletion.
Particularly high levels of CO2can occur in ponds after phytoplankton
die-offs, after a turnover and
during cloudy weather. Under
these conditions, oxygen
concentrations in the water may be
low and the increased levels of CO2 can interfere with the fish's ability
to use any available oxygen. In
situations with low oxygen and
high carbon dioxide levels,
emergency mechanical aerators
will increase oxygen in the water and help lower CO2 levels. Ammonia The effects of ammonia on fish are
poorly understood; however, there
is evidence that sublethal levels
adversely affect fish. Ammonia
toxicity can be a problem in
holding tanks, live-haul tanks and aquaria. Unionized ammonia (NH3) is much more toxic to fish than ionized
ammonia (NH4+). Of the total amount of ammonia in water, the
percentage of the unionized form
increases with increasing pH. Thus,
the toxicity of ammonia is pH
dependent. Concentrations as low
as 1.5 ppm ammonia have been reported to be toxic to channel
catfish. Ammonia accumulates in
water through excretion by fish
and as a natural product of decay.
Most of the nitrogen excreted by
fish is in the form of ammonia. Accumulation of ammonia in pond
water is usually associated with
conditions leading to an oxygen
depletion. Water test kits are
available to determine ammonia
levels. Nitrite Nitrite toxicity in fish is called
brown blood disease. Fish suffering
from nitrite exposure have blood
the color of chocolate milk. Because
nitrite interferes with oxygen
uptake by blood hemoglobin, the symptoms of nitrite poisoning are
very similar to an oxygen
depletion. However, fish are likely
to show symptoms any time of the
day, unlike an oxygen depletion
where symptoms are most likely near sunrise. In intensively managed catfish
ponds, nitrite levels should be
checked every two or three days. If
nitrites are detected, the water
should be analyzed for chlorides.
Symptoms and effects of nitrite toxicity can be prevented or
controlled by adding salt (sodium
chloride) to ponds at
recommended rates.

Share this: