After 35 days posthatching, the highest values of average weight (3.50 g) and the highest survival rate (94%) of tilapia were recorded in fry treated with 60 mg 17a-MT /kg diet compared to those of fry treated with 40 mg 17a-MT/kg diet, 80 mg 17a-MT/kg diet or in the untreated control group. On the other hand, the lowest values of average weight (2.81 g) and lowest values of survival rate (60%) were recorded in tilapia treated with 80 mg 17a-MT/kg diet as recorded in Table 2.