Monosex production of tilapia, Oreochromis niloticus using different doses of 17α-methyltestosterone with respect to the degree of sex stability after one year of treatment

With the purpose of solving some practical problems concerning the complete masculinization of Oreochromis niloticus by oral administration of 17α-methyltestosterone (17α-MT) with respect to the dose of the hormone used, different doses of 17α-MT (40, 60 and 80 mg of 17α-MT/kg of feed) were orally administered to sexually undifferentiated fries from the 7th to the 28th day posthatching to produce all male tilapia population.After 15, 35 and 75 days and 1 year of treatment, growth parameters, survival rate, sex ratio and gonad histology of the resulting larvae and fish were demonstrated. The results showed that the highest survival rates of the fry were recorded in the group treated with 60 mg of 17α-MT/kg of feed compared to the control group, 40 and 80 mg of 17α-MT/kg of feed treated groups. The maximum sex ratios of males (95% and 97%) were recorded at 60 mg of 17α-MT/kg of diet after 75 days and one year of treatment respectively.After the first year, the degree of sex stability was observed significantly shifted towards males. The histological examination showed that the treatment caused an increase in male gonad recrudescence in most of the treated fish. In presumed genetic females, there are oocytes of young stages, gonial germ cells and different stages of degenerating oocytes within the period around 35 days posthatching.The present results concluded that 17α-MT has a potential effect in directing gonadal sex differentiation of OreochromisOreochromis niloticus towards males according to the dose involved in the treatment.