The present experiment was carried out to investigate the effect of rearing water temperature in combination with or without hormone application on masculinization of newly hatched O. niloticus fry. Nile tilapia fry (0.025 g) were reared in three levels of temperature 25, 30 and 35°C and in each rearing temperature fry were fed diet with or without supplementation of 60 mg 17α-methyltestosterone (MT) for 7, 14, 21 and 28 days.
O. niloticus fry fed diet without MT and reared at different water temperature 25, 30 and 35°C significantly increased the male ratio from 48.67 to 48.67 and 65.33% after one week; 48.67 to 64.00 and 72.67% after two weeks; 48.67 to 68.67
and 77.33% after three weeks and 48.67 to 80.67 and 84.00% after four weeks,respectively. While fry fed diet supplemented with MT with increasing rearing water temperature from 25 to 30 or 35 °C significantly increased male percentage from 58.00 to 84.67 and 86.00% after one week; 67.66 to 93.33 and 96.67% after two
weeks; 79.00 to 97.33 and 98.67% after three weeks and 85.67 to 98.00 and 99.33% after four weeks.
Mortality rate for O. niloticus fry reared at different water temperature 25, 30 and fed diet without MT significantly increased from 10.33 to 14.00 and 14.33% after one week; 10.33 to15.33 and 15.00% after two weeks; 10.33 to 15.33 and 1517% after three weeks and 10.33 to 15.83 and 16.83% after four weeks. But, supplementation of
O. niloticus feed diet supplemented with MT and increasing rearing water temperature from to 30 or 35°C significantly increased mortality rate from 14.67 and 14.00% after one week; 16.00 and 15.67% after two weeks; 15.33 and 15.67% after three weeks and 16.00 and 17.33% after four weeks of treatment.
The highest fry body weight was recorded for fry group administrated with MTand reared at water temperature of 35°C and the opposite trend was observed with fry group reared at the lower temperature (25°C) and fed diet without MT.