Optimization of Feminization of Oreochromis niloticus L. by Oral Administration of Diethylstilbestrol (DES): The Effects of Stocking Density, Treatment Duration and Environment

Abstract

The effects of the treatment environment (tank and hapa), duration of treatment, and stocking density of fry on the success of feminization protocols were investigated. In the first of two studies, the fry were hormone-treated in concrete tanks (clear water) and hapa-inpond environments for three durations: 10, 15 and 20 days. All groups were administered diethylstilbestrol at 1000 mg•kg-1 of feed and stocked at 1000 fry m-2 . In the second study, fry were treated in hapas at three stocking densities: 1000, 2500 and 5000 m-2 . A shorter treatment duration of 10 days was sufficient for effective feminization (>90% phenotypically female populations) of fry held in tanks, whereas 15-20 days was required for effective treatment in hapas. Stocking density greater than 1000 fry m-2 did not significantly increase the induction of feminization but significantly reduced the growth and survival rate of the fish. The optimum feminization protocol is feeding DES at 1000 mg•kg-1 to fry held at 1000 m-2 for a treatment duration of 10 days in tanks and 15-20 days in hapas.