Effect of synthetic androgen treatment on the gonad of juvenile longtooth grouper (Epinephelus bruneus)

Commercially significant groupers are protogynous hermaphrodites. Since their sex change from female (ovary) to male (testis) occurred in a larger size and older age, capturing or maintaining males in the aquaculture farm is very difficult. In the present study, juvenile longthooth groupers (2+ years old) were implanted with two doses of 17alpha-methyltestosterone (MT) cholesterol pellet (2 mg or 5 mg MT kg-1 BW) for the induction of artificial sex reversal. Individuals were sampled at 30 and 80 days after treatment. All the control group fish had immature ovaries contained with primary oocytes and germ cells. Fish treated with MT for 30 days had sex-transitional gonad consisted of few primary oocytes and testicular tissues. By using immunohistochemistry, we identified the proliferating and apoptotic cells in the gonad of this sexual stage. After 80 days for MT treatment, gonads of all individuals were filled with germ cells at all stages of spermatogenesis, and the newly formed efferent duct contained active spermatozoa. Since sperm motility was confirmed, MT treatment successfully induced functional sex reversal in pre-pubertal longtooth grouper. This method may dramatically reduce the cost and time required for the production of longtooth grouper.