FRY REARING AND MANAGEMENT
Eggs
produced after spawning hatch into; yolk materials act as a source of food for
the young fish. The time of hatching (incubation period) varies according to
species and is temperature dependent. For Clarias gariepinus in Nigeria, the
preferred hatching temperature is from 25o c to 29oc and 24 to 36 hrs after fertilization.
Newly hatched fry searches frantically for food, protection and at this time,
the fish is very vulnerable to predation. Thus, the fry needs food, protection
and a fry rearing is carried out in nursery tanks, raceways and ponds. These
are always protected against predator and the water quality is constantly
monitored. Nursery facilities can be small-, average size or large-scale
depending on the extent of the hatchery operations. The early food of the fry
has been pre-determined and suitability and performance of natural planktonic
organisms established. The brine shrimp, Artemia salina, is popularly used
especially in large hatcheries and in recirculation system as the first food of
fry in nursery tanks and troughs. Zooplankton (especially monia) culture is
also widely used in many fish farms especially with the high cost of importing Artemia. Artifical diets are always introduced
at age between seven to ten days.
Fry rearing is the most critical
stage in catfish seed production in Nigeria. In most hatcheries, between 70
and 90 percent fry are lost before reaching fingerling stage (i.e. about six weeks). Fry rearing and
management require traning and expertise. Only sophisticated hatcheries achieve
more than 50 percent survival.
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