UNDERSTANDING ARTIFICIAL REPRODUCTION OF CATFISH

Catfishes are the group of fish species belonging to the family claridae inhibiting marine, estuaries and freshwater habitats. These are predatory fish generally preferring mud ground they also feed on terrestrial insects, mollusc and fruits.The large African species which are of interest for aquaculture belong to the Subgenus Clarias.

This species of catfish has been considered to hold a great promise for fish farming in Africa. This because it has high growth rate, high resistant to handling and stress and is highly appreciated in most of African countries engaging in fish farming system.

ARTIFICIAL REPRODUCTION

There are two forms of artificial reproduction Semi natural or hormone induced reproduction. 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 induced 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 unfavorable environmental conditions. Better conditions for growth and survival. The hormones used in induced reproduction are DOCA (Desoxycorticosteroid Acetate), HCG (Human Chorionic Gonadotropin), Common carp (cyprinus carpio) pituitary gland material, Pituitaries of the African catfish (C. gariepinus). A female catfish will respond once it injected with a pituitary of a catfish (male or female) of equal size.

PROCEDURES FOR ARTIFICIAL REPRODUCTION.

Broodstock care and selection of ripe breeders

In most cases broodstock selected from nature or bought at a fish farm are kept in earthen ponds at stocking density of 0.5-1/m2 and fed regularly with agriculture waste products and sometimes with some trash fish. Egg development will take place and about six week after a female has been reproduced it can be used again. In some areas of Africa the water temperatures drops below 22 ⁰c during the dry/winter season, which hampers the egg development and artificial reproduction.

Hormone injection

The most common technique employed to induce final maturation and ovulation in African catfish is to inject the female with hormones or pituitary gland material. The required quantity of powdered acetone dried pituitary material or the required number of whole pituitaries are pulverised in a porcelain mortar, mixed with the required quantity4 of physiological salt solution (9 g of common salt/litre of water). A syringe is filled with the suspension and the injection can be given.

 The most common method of administering the hormone solution, is by intra-muscular injection into the dorsal muscles. Normally the females are injected in the afternoon/evening and are kept (separated from the males) in holding facilities. The holding facility can be a concrete basin inside a hatchery, a happa in a pond or even a simple plastic bucket or a half oil drum will do. Of major importance is that the breeders can be caught easily the morning after injection so as to avoid spoilage of eggs.

Maturation processes and stripping of the eggs

The process of final maturation (migration of the nucleus to the animal pole, fusion of the yolk, breakdown of the germinal vesicle followed by first meiotic division) and ovulation (rupture of the follicles and accumulation of the ripe eggs in the ovary cavity) cannot be stopped or reversed after administration of the correct hormone dosage. Once these processes start the eggs must either be spawned or stripped. Stripping of the female spawners is carried out by gently pressing their abdomen with a thumb from the pectoral fin towards the genital papilla. Ovulated eggs will flow out easily in a thick jet from the genital vent and are usually collected into a dry plastic container.

Milt collection and fertilization

The males of the African catfish cannot be stripped and consequently the sperm can only be obtained by sacrificing a male. The male is killed and the body surface thoroughly dried after which the testis is dissected and placed in a mortar or a teacup. The testis is rapidly cut into small pieces using a scissor and finally the milt is pressed out with a pestle or a teaspoon.

The sperm (diluted or non-diluted) is added to the stripped eggs, and the eggs fertilized by adding an equal volume of clean water.The water and egg mass are then mixed by gently shaking of the bowl. Eggs must be stirred continuously until they are placed in the hatching tanks as the eggs become sticky and without stirring will stick together into one clump.

Incubation of fertilized eggs.

The development process from fertilized egg to hatching, like all other biological processes, is dependent upon water temperature; the higher the water temperature the faster the eggs hatch. A general principle of egg incubation is that water is renewed in order to provide oxygen and that after hatching the new born larvae are separated from the remaining egg-shells and dead eggs. The latter is of most importance in order to avoid fungal infections of hatchlings and consequent larval mortalities

Artificial propagation of catfish video