Effect of a non steroidal tamoxifen on the gonad and sex differentiation in Nile tilapia, Oreochromis niloticus.

The effect of different doses of anti-estrogenic chemical was studied in a cichlid Oreochromis niloticus on mortality, growth, sexual development and sex differentiation. Percent mortality (5, 10 and 10) appeared to be dose-dependent. All groups of tamoxifen (TA) treated fishes exhibited significant growth as compared to the controlled fishes. Immature fishes treated with TA at 200 microg l(-1), showed lower gonado-somatic-index (GSI) (male 0.137; female 0.118) than control group (male 0.138; female 0.122) of fishes. Ovarian and testicular differentiation was adjudged by the appearance of the ovarian cavity (ovary) and the efferent (sperm) duct (testis), respectively. Sex and sexual maturity of individual fishes were determined using standard histological method. Tamoxifen treatment to the fry (yolk sac absorbed stage) of Oreochromis niloticus in the dose of 200 microg l(-1) for 60 days produced 90% males and 1% intersex population. Results suggested masculinizing action of tamoxifen reversing the sex of genetic female tilapia.