Seasonal dynamics of plasma estradiol 17β level, gonadosomatic index, and ovarian development in female golden trevally (Gnathanodon speciosus)

Plasma estradiol 17β (E₂) and gonadosomatic index (GSI) are reliable biomarkers for assessing gonadal maturity in fish. This study investigated seasonal variations in GSI and plasma E₂ concentrations and their correlation with ovarian development stages in female golden trevally (Gnathanodon speciosus), a high-value fish species for marine aquaculture, over an annual reproductive cycle. The broodfish were 900 ± 200 g and 40 ± 5 cm in body weight and total length, respectively. From November to February, plasma E₂ levels and GSI remained low, followed by a significant increase from March to October, with E₂ peaking during vitellogenesis. Ovarian histology revealed asynchronous oocyte development from March to October, with multiple oocyte stages coexisting, confirming G. speciosus as a multiple-spawning species with a reproductive season spanning March to October. Elevated plasma E₂ levels during oocyte growth underscore its pivotal role in driving vitellogenesis. These findings enhance understanding of G. speciosus reproductive physiology, providing valuable insights for optimizing broodstock management, conditioning protocols, and strategic planning for artificial reproduction and seed production for marine aquaculture.