New Techniques for the Artificial Brooding of Eggs and Young of Oral-Brooding Tilapia Species

Abstract

METHODS, MATERIALS AND RESULTS The three methods to be described all devolve on the principle that a constant temperature and movement of the surrounding freshwater are primary factors in a successful artificial brooding of eggs and fry. After successful mating the brooding partner is allowed to incubate the eggs overnight to allow for complete fertilization. The brooding partner (which is, so far as is known, consistently the female in the East and Central African species of Tilapia), is now very carefully removed from the breeding aquarium. This obviates the" spitting" of the fertilized eggs by the brooding parent. This is best done by carefully and gently inducing the brooding partner, generally very sensitive during this period, to enter a bucket or large five-litre beaker lowered into the aquarium. The fish is now caught by hand and firmly held. It is important that the fish is approached gently by hand and that it is held firmly subsequently since it can easily jump out and spit out all the eggs. Provided this risk is avoided by approaching the fish gently and holding it firmly once caught, it is quite easy to induce release of the eggs into the receptacle without any spillage. If the fish is held by the right hand, the right index finger is used to raise the upper lip while simultaneously the left index finger is used to lower the lower jaw. By immersing and withdrawing the fish into the water in the receptacle, the entire batch of fertilized eggs are released into the latter. The above procedure is common to all the methods. The variations are in the equipment used subsequently. Temperature shocks should be avoided by prior adjustment of the equipment temperature to that of the water in the breeding tank. Subsequent rises in temperature can be made provided these are done slowly. After the complete resorption of the yolksac, the young were fed on brine shrimp larvae on which they thrived well.