The increasing world-wide importance of cultured tilapia as a food fish has
prompted considerable research on genetic improvement of the commercially
important species. Much of this work has concentrated on the development
of chromosome-set manipulation techniques with varied applied objectives.
The most common rationale has been the production of sterile triploid off-
spring to negate the problem of precocious sexual maturity and unwanted
reproduction in culture, first attempted in Oreochromis aureu~ by Valenti
( 1975 ) . More recent studies have attempted gynogenesis and androgenesis
with the objectives of elucidating sex-determining mechanisms and develop-
ing techniques for genetic manipulation of these mechanisms to produce
monosex male populations for culture ( Avtalion and Don, 1990; Pandian and
Varadaraj, 1990; Mair et al., 199 1 a, 199 1 b). In addition these techniques may