Sex Reversal of Tilapia: 17α-Methyltestosterone Dose Rate by Environment and Efficacy of Bull Testes

Sex reversal of newly hatched tilapia generally is accomplished via oral administration of 17α-methyltestosterone (MT), which has been incorporated into a starter fish feed at 60 mg MT/kg feed (Popma and Green, 1990). Although the use of the 60 mg MT/kg feed dose consistently yields populations comprised of less than 5% females (i.e., > 95% males), this has not been shown to be the optimal dose. Other investigators have reported sex reversal of tilapia at dose rates less than 60 mg MT/kg feed (Guerrero, 1975; Tayamen and Shelton, 1978; McGeachin et al., 1987; Jo et al., 1988; Varadaraj and Pandian, 1989); however, results from some of these studies are inconsistent, and it is difficult to separate treatment environment effects. Thus, it is necessary to identify the optimal dose of MT for consistent, successful sex reversal in a variety of treatment environments.