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The dusky grouper, Epinephelus marginatus, is a protogynous monandric hermaphrodite species, since individuals mature firstly as females and later as males. This makes capture and maintenance of males in captivity difficult due to their large size and older age. Thus, the use of techniques that allow controlling sex, obtaining smaller and younger males, as well as cryopreservation techniques to improve sperm availability, may contribute to improve dusky grouper reproduction in captivity. In the present study, immature fish and young females were sex reversed using 2.5 mg/kg BW 17α-methyltestosterone (α-MT) in silastic implants, two months prior gamete extraction. In all individuals a single dose of Lucrin Depot® (20 μg/kg BW, GnRHa) was enough to induce and/or increase sperm production. Volume of sperm, cell concentration, osmolarity, sperm production and motility were registered. Sperm was …