Gonad development during sexual differentiation in hatchery-produced orange-spotted grouper (Epinephelus coioides) and humpback grouper (Cromileptes altivelis) (Pisces: Serranidae, Epinephelinae)

Juvenile sexual differentiation of two commercially important epinephelines, orange-spotted grouper (Epinephelus coioides) and humpback grouper (Cromileptes altivelis) (Serranidae, Epinephelinae), produced in hatcheries, was studied until first sexual maturation using gonadal histology. Diandric, protogynous hermaphroditism is confirmed for E. coioides with evidence of primary male differentiation directly from the juvenile phase as well as of secondary male development through the sex-change of functional females. All juveniles developed first an ovarian-phase then entered a bisexual-phase gonad. Sexual differentiation occurred in bisexual gonads at around 105 weeks after hatching (wah), with the growth of oocytes beyond the primary-growth stage for females, and the appearance of sperm sinuses and proliferation of spermatogenic cysts in primary males. The minimum size and age of first sexual maturation for females were 355 mm standard length (SL) and 113 wah. No mature males were found by 141 wah, suggesting that first maturation in males takes longer than in females, at least under mariculture conditions. For C. altivelis, all juveniles developed an ovarian-phase gonad. Minimum body size and age of first sexual maturation for females were 155 mm SL and 83 wah. In contrast to E. coioides, there was no sign of spermatogenic cysts in juvenile gonads and any indication of primary male differentiation in C. altivelis. This study reveals the variation in early gonad development in the epinephelines and highlights the importance of studying juvenile sexual differentiation for fully understanding sexual pattern in this fish subfamily.