Effects of Estradiol Valerate on Steroid Hormones and Sex Reversal of Female Rice Field Eel,Monopterus albus (Zuiew)

The rice field eel, Monopterus albus (Zuiew), is an important aquaculture fish in many Asian countries. Productivity, however, is limited by low fecundity as a result of sex reversal of female juveniles of this fish. This study was conducted to investigate the effects of estradiol valerate on the sex reversal process of this fish by determining sex changes of initial 2‐yr‐old female eels (26.5 ± 2.6 cm, 21.9 ± 2.1 g) treated with three concentrations of estradiol valerate: 0 mg/kg (Control, Group A), 10 mg/kg (Group B), and 50 mg/kg (Group C). In Group A, sex reversal took place with significantly higher percentage of sex change: about 45% of female eels to intersexes and males. Only about 22% of female eels changed to intersexes and males in Group B, but no sex reversal occurred in Group C during the experimental period. The result also indicated that the gonadal development and the concentrations of serum estradiol (E₂) and testosterone (T) varied significantly with different concentrations of dietary estradiol valerate. Serum T significantly reduced but serum E₂ significantly increased in Group C compared to the control Group A. The results demonstrated that estradiol valerate affected the secretion of sex steroid hormones in rice field eels and thus inhibited the sex reversal process at a low concentration (10 mg/kg) or stopped the sex reversal process at a high concentration (50 mg/kg) of estradiol valerate. These results suggest that a higher yield of mature female eels could be achieved by treatments with estradiol valerate, thus enhancing the fecundity of this rice field eel.