Induction of precocious sex reversal in aquaculture: effects of methyltestosterone treatment on gonadal sex of yearling longtooth grouper (Epinephelus bruneus)

Groupers, highly valued fish globally, exhibit sex change from female to male during adulthood, posing challenges in obtaining wild males for aquaculture. Inducing female-to-male sex reversal in juvenile groupers can streamline breeding efforts. This study used 17a-Methyltestosterone (MT)-loaded cholesterol pellets to treat one-year-old longtooth groupers (Epinephelus bruneus) and induce small functional males. Gonadal sexuality and male functionality were assessed after one to two months. Initial gonadal changes included efferent duct differentiation. High-dose MT-treated fish exhibited active spermatogenesis. However, no spermiation was observed. This highlights MT s potential for sex reversal but not for complete testicular function. These findings have implications for grouper aquaculture and the management of sex change. Further research should explore methods to optimize functional male induction for sustainable breeding practices.