Ornamental Fish Production and Management

8.1.5 Breeding of live bearers

In live bearing fish, the eggs are situated in the egg duct where they are fertilized. Upon hatching, the fry are not immediately delivered, but they remain in the safety of the mother’s body until they reach a stage of development equivalent to the young of egg layers that have absorbed the yolk sac and become free swimming. The ideal temperature must be 27^oC.

As the male matures, the anal fin becomes more pointed and straightened into a rigid tube like projection, which is called gonopodium. The gonopodium is carried normally close to the body and pointing rearwards. However, it is a mobile organ and can be angled in almost any direction. The males court the females with their fins erect and they chase the female untill the opportunity presents itself for a lightening thrust of the gonopodium. The female is fertilized by the nearest touch of the gonopodium on her vent, and one fertilization will last for several broods. Unlike the male, the female has normal analfin. Females can have upto eight broods from one fertilization therefore it is unnecessary to remate after the first brood. The period of gestation is being constant for every species.

Females about to give birth are said to be ripe. This condition can be determined by the appearance of the dark, crescent shaped area in the female body close to the vent known as the gravid spot, which is accompanied by a general fattening of the belly when viewed from above. The eggs develop and actually hatch out inside the mother and leave her body as fully developed fish. The number of young in a brood is largely dependent upon the size of the female. Irrespective of the number in the brood the fry are approximately all the same size at birth. Livebearers are notorious cannibals; they will devour their youngones as soon as they are born. This can be prevented by having an abundance of cover for the youngones in the form of bunched fine leaved plants, or to use a breeding trap, which restricts the female to a small part of the aquarium, but allows the fry to escape into the wider reacher of the breeding tank.

The preparation for the breeding tank is simple. It need not be too large for most species, and should be filled to a depth of about 8” (20cm) with matured water and the temperature is raised to about 25^oC. The tank should be well stocked with fine leaved plants. Once the female has given birth to the full brood she can be removed. Instead of plants, nylon knitting wools can also be used. Handling livebearers when they are near the time to delivery can cause premature birth. Premature babies have not completely absorbed their yolk sac, which can be seen attached to their bellies.  Livebearers normally kept in a community aquarium tank will breed indiscriminately, and will often crossbreed between similar species. If the aquarist is interested in obtaining a particular colour strain or any other feature for that matter it is imperative that the sexes are housed separately.