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

Sex change Sex reversal Gonad Ovary Testis

Authors

  • Yasuhisa Kobayashi Laboratory for Aquatic Biology, Department of Fisheries, Faculty of Agriculture, Kindai University, Nakamachi 3327-204, Nara 631-0052, Japan.
  • Otoya Keyamura Aquaculture Research Institute, Kindai University, Shirahama 3153, Wakayama 649-2211, Japan.
  • Mark P. Lokman Department of Zoology, University of Otago, Dunedin, New Zealand.
  • Hisashi Chuda Aquaculture Research Institute, Kindai University, Shirahama 3153, Wakayama 649-2211, Japan.
December 25, 2023

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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.