Histological description and endocrine regulation of ovarian maturation in wild and captive white-streaked grouper Epinephelus ongus

Information regarding the endocrine regulation of oocyte maturation in cultured species is essential for the artificial seed production. To elucidate endocrine mechanisms that underlie oocyte maturation of the white-streaked grouper, Epinephelus ongus, a commercially important fish species, we collected and compared data linked to the ovaries of captive and wild white-streaked grouper specimens, and plasma steroids data were obtained using captive fish. This data allowed for a comparative analysis of the ovarian development of both groups; the comparison was necessary for the acquisition of physiological patterns universally representative of the species at hand. The dynamics of the gonadosomatic index (GSI) and oocyte development of both groups confirmed that vitellogenesis progressed toward the last quarter moon, final oocyte maturation began the day before the last quarter moon, and spawning occurred after the last quarter moon. These results indicate that the changes in ovarian development and GSI in wild and captive fish were synchronous, and that the endocrine changes observed in captive fish represent those that occur in wild fish. The changes in estradiol 17 beta (E2) levels in captive fish increased and decreased during the vitellogenic and final oocyte maturation phases, respectively. These dynamics were similar to those of GSI. We found that 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (DHP) was consistently detected at concentrations higher than those of 17 alpha, 20 beta-21-trihydroxy-4-pregnen-3-one (20 beta-S); this trend was constant across all stages of ovarian development. In contrast, 20 beta-S was detected at lower concentrations than DHP in all captive individuals, but at higher levels after the onset of final oocyte maturation. These results suggest that 20 beta-S and/or DHP may be maturation-inducing hormones (MIH) in this species. Our results also highlight the importance of integrative analyses of wild and captive individuals to comprehensively elucidate the endocrine regulation of cultured species of interest to improve aquaculture management practices.