Abstract: Studies were conducted to reveal the growth differences between female and male Nile tilapia (Oreochromis niloticus) by identifying the gender with molecular marker, acid red dyeing method and histological section, meanwhile, the content of serum steroid hormones, testosterone (T) and estradiol (E₂), were also investigated. Results showed that the total length, body weight in the female and male began to show significant differences (P <0.05) at 3.0 and 2.5 months age, respectively. Simultaneously, the Logistic growth equation can be expressed as L_t(♀)=16.443/(1+e^{(2.821-1.363*t)}), L_t(♂)=18.248/(1+e^{(2.72-1.295*t)}), W_t(♀)=107.704/(1+e^{(5.157-1.464*t)}), W_t(♂)=134.796/(1+e^{(5.080-1.417*t)}). The inflection point for the body weight growth was 3.523 month in the female and 3.585 month in the male, and the corresponding weight was 52.352 and 67.398 g, respectively. The growth rate of total length and body weight in the male was throughout larger than that in the female. Furthermore, the male showed longer period and heavier increment than the female in the fast-growing period. After 3.0 months age, the content of E₂ and T between the male and female was significantly different(P<0.05), respectively. Results suggested that the relative content of E₂ and T may result in the growth difference between the male and female Nile tilapia.

Key words: Oreochromis niloticus, female and male, steroid hormones