ARTIFICIAL REPRODUCTION
5.2.1 GONADAL DEVELOPMENT IN CAPTIVITY
The
female Africa catfish has a fully development ovary which contains “ripe” eggs
the whole year through, if kept in ponds and once the water temperature remains
above 220c. The eggs of a “ripe” female make up 15-20% of the body
weight (i.e. a “ripe” female of 1 kg having about 150-200 gram of “ripe” eggs).
The oocyte development decreases once the temperature drops below 220c
and we see that the ovary makes up approximately 5% of the body weight of the
female. Artificial reproduction is still possible but the number of eggs
obtained is small and the quality of the eggs decrease as can be seen from the
decrease hatching percentage.
In general the testis of a male is fully
developed at age 8-12 month once they reach a weight of approximately 200 g.
Sperm could be obtained the whole year through and no impacts of temperature on the availability of
sperm was found. In captivity, the Africa Catfish does not spawn spontaneously
since the environmental factors such as the rise in water level and inundation
of shallow area do not occur on the fish farms. Since the early 1970’s several
techniques have been developed (with or without hormone treatment) for the
artificial reproduction of the Africa catfish.
Semi
natural or hormone induced reproduction within ponds or concrete tanks as
described above can be used on small farms to produce their own larvae and
fingerlings. However, the method has not proved to be a reliable method for
mass production needed for lager fish farms or distribution centres of catfish
fingerling. Therefore artificial propagation under more controlled conditions
including; stripping of eggs, collection of the sperm, followed by
fertilization of eggs has been developed.
Artificial
reproduction by induces breeding through hormone treatment followed by
artificial fertilization and incubation of fertilized eggs and the subsequent
rearing to fingerling size has several advantages including:
·
Better rates of fertilization and
hatching
·
Protection against enemies and
unfavourable environmental conditions; and
·
Better conditions for growth and
survival.
The artificial reproduction of the
Africa catfish, as for all fishes, consists of a chain of activities which is
more or less similar to that which occurs during the course of natural reproduction.
5.2.2 TYPES OF HORMONES USED IN INDUCING REPRODUCTION
For hormone induced reproduction
(semi artificial or artificial) the following hormones are generally used;
v DOCA
(Desoxycorticosteroid Acetate), 2.5-5 mg per 100 gram of female. A disadvantage
of using this hormone is that it is mostly suspended in oil which causes severe
ulcers on the injected female.
v HCG
(Human chorionic Gonadotropin), 25 I.U. per 100 gram of female. This hormone
works well but it is expensive.
v Common
carp (cyprinus carpio) pituitary
gland material, 3-4 mg per kilogram of female or 1-2 whole pituitaries per
female. In general, the common carp pituitary gland material has to be imported
from aboard which means that it is usually not accessible for small fish farms.
v Pituitaries of the Africa catfish (C. gariepinus). A female catfish will
respond once it is injected with a pituitary of a catfish (male or female) of
equal size. Most commonly sued in Nigeria is ovaprim.
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