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. Therefore, three rearing temperatures 25, 30 and 35°C were investigated. For each rearing temperature, fry divided into two groups, supplemented or not not suplemented by 60 mg 17α-methyltestosterone (60 mg 17α-MT).
Increasing rearing water temperature from 25 to 30 or 35°C without supplementation by 60 mg 17α-MT(C30H0 and C35H0) significantly increased male ratio from 48.67 to 48.67 and 65.33% after one week; 64.00 and 72.67% after two weeks; 68.67 and 77.33% after three weeks and 80.67 and 84.00% after four weeks of treatment, respectively. While supplementation of O. niloticus fry with 17α-MT with increasing rearing water temperature from 25 to 30 or 35 significantly increased male percentage from 48.67 to 84.67 and 86.00% after one week; 93.33 and 96.67% after two weeks; 97.33 and 98.67% after three weeks and 98.00 and 99.33% after four weeks of treatment.
Increasing rearing water temperature from 25 to 30 or 35°C without 17α-MT (C30H0 and C35H0) significantly increased mortality rate to 14.00 and 14.33% after one week; 15.33 and 15.00% after two weeks; 15.33 and 15.17% after three weeks and 15.83 and 16.83% after four weeks of treatment. While supplementation of Nile tilapia fry feed by 17α-MT with increasing rearing water temperature from to 30 or 35°C (C30H1 and C35H1) significantly increased mortality rate to 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 BW were recorded for fry group administrated 60 mg 17α-MT/kg feed and reared at water temperature of 35°C and the opposite trend was observed with control fry group which did not supplemented with 17α-MT and reared the lower water temperature (25°C).
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