Induction of sex reversal in longtooth grouper Epinephelus bruneus by implantation of 17-alpha-methyltestosterone cholesterol pellets

Sex reversal from female to male in the six-year-old longtooth grouper Epinephelus bruneus (mean body weight, 3.1 kg) was induced by the implantation of 17-alpha-methyltestosterone (MT) cholesterol pellets. We compared the efficacy of the cholesterol pellets at MT doses of 1 mg/kg BW (group A) and 2 mg/kg BW (group B) implanted in February, as well as 2 mg/kg BW implanted in April (group C). At 4 months after the treatment, 67% of the fish in groups A and B had been transformed into males. On the other hand, all fish in group C had been transformed into males at 2 months after the treatment, and all group C fish remained male even at 14 months after the implantation. These results indicate that the implantation of MT cholesterol pellets at a MT dose of 2 mg/kg BW in April is an effective and long-lasting treatment for inducing sex reversal in the longtooth grouper.