Primary male development of two sequentially hermaphroditic groupers, Epinephelus akaara and Epinephelus awoara (Perciformes: Epinephelidae)

Gonad ontogeny of the Hong Kong grouper Epinephelus akaara (a bi-directional sex changer) and the yellow grouper Epinephelus awoara (a protogynous hermaphrodite) was examined for the first time from post-larval phase until first sexual maturation, by histology. Approximately 20 specimens of each species were collected randomly every 2-7 weeks from rearing tanks with natural sea water and temperature between June 2013 and June 2014. The paired gonadal primordia (GP) were observed at 6 weeks after hatching (wah) for both species; however, gonia were first observed in GP at 16 wah for E. akaara and at 8 wah for E. awoara. The timings for the appearance of primary-growth stage oocytes (O1) and the completion of ovarian lumen (OL) varied; both at 27 wah for E. akaara, and at 18 and 23 wah for E. awoara respectively. A bisexual-phase gonad with an OL, O1 and scattered spermatogenic cysts (SC) was observed at 27-29 wah for both E. akaara and E. awoara. Sexual differentiation was subsequently observed from the bisexual-phase gonad at 34 wah for E. akaara, and 41 wah for E. awoara, with the appearance of cortical-alveolus stage oocytes (O2) for developing female and the proliferation of SC for developing primary male (i.e. from juvenile directly). Ovaries of mature females contained the vitellogenic stage oocytes (O3) and scattered SC; testes of mature primary males had sperm in sperm sinuses within the gonadal wall and remained O1. Minimum age of first sexual maturation for both female and primary male of E. akaara was at 41 wah; minimum total length (LT ) of female (143 mm) was larger than that of primary male (137 mm L(T)). Minimum age and size of first sexual maturation for female of E. awoara (47 wah and 149 mm L(T), respectively) were larger than those of E. akaara. Developing primary males of E. awoara were found at 41-58 wah, however, mature males were not observed, indicating inconsistency in first sexual maturation for E. awoara. This study provided strong evidences of primary male pathway in E. akaara and E. awoara; the latter is confirmed to be diandric.