Abstract: Neojifu tilapia ( Oreochromis niloticus ) fry with body length varying from 0.7 cm to 1.9cm were fed diets containing different levels ofestradiol benzoate (EB) hormone to induce feminization ofXY neofemales for YY super males twice a daily from July 12th to October 21 st of 2009 and from May 1 st to November 6th of 2010. The fish fed the diet containing EB at a dose of 100 mg·kg^-1 were found to have 80.0% of females in 26 d, 93.4% of females in 36 d, 93.9% of females in 46 d, and 94.0% of females in 59 d and reared for 102 d, 25.2%, 38.6%, 39.1%, and 39.2% higher than that in the control group (54.8%), respectively. There was 83.1% of females in the fish fed the diet containing 200 ·kg^-1 EB for 24 d and reared for 188 d, 36.2% higher compared with the control group (46.9%), and very significant differences by X2 test in the two experiments (P〈0.001). There were no significant differences in the survival rate between the test fish and the control ones, and no abnormal fish were observed. It was found that the final body weight and final total length were very sig- nificantly and significantly smaller in the fish in the two experimental groups than those in the control group(P〈0.01, P〈0.05). There was no significant difference in growth between the experimental sex non-reversal males and the control males (P〉0.50). Thus, it is optimization of feminization protocol that neojifu tilapia fry are fed a diet containing EB at a dose of 200 mg·kg^-1 for about 35 d.

Key words: estradiol benzoate (EB), neojifu tilapia Oreochromis niloticus, feminization, survival rate, growth