SEX CONTROL IN FISH BY SEX STEROID HORMONES

Abstract

The effect of the synthetic male hormone 17a-

methyltestosterone (MT) was studied on Nile tilapia Oreochromis niloticus phenotypic sexual differentiation. Fourty five hundreds undifferentiated Nile tilapia fry were divided into four experimental groups and control. For the first and second groups, ?days old fry were fed on 60 ppm MT treated feed for 21 and 28 days, respectively. For the third and fourth groups, 14 days old fry were fed on 60ppm MT treated feed for 21 and 28 days, respectively. The fry of the control group were divided into two subgroups, one was fed on diet without hormone and solvent and the other was fed on ethanol treated feed and was utilized as a vehicle control. Fry were fed at approx. rate of 20% of body weight twice daily. At 100 days of age fish were dissected, the gonads were classified on the basis of microscopic appearance. The dissected gonads w8re stained by aceta - carmine squash method. Ovarian tissue was positively identified by the presence of oocytes. The hormonal treatment resulted in male population ranged from 79.4 to 98.9% as compared to 53% for the control. Hormonal treatment resulted in higher body weight, total body length , body weight gain , growth rate and survival rate than control .