Estradiol-17β and testosterone levels during the annual reproductive cycle of in Mytilus coruscus

The aim of the study was to examine seasonal variations in the estradiol-17β (E2) and testosterone (T) levels in the gonad of Mytilus coruscus in relation to the reproductive cycle. M. coruscus individuals were obtained from March 2012 to February 2013 and gonadal tissue was studied by histological analysis and transmission electron microscopy. Histological data revealed that gametogenesis occurs from autumn to winter (i.e., from September to January) when the water temperature is lower than the rest of the year, and spawning occurs in spring (i.e., March onwards). In this study, we used enzyme-linked immunosorbent assay (ELISA) to measure the estradiol (E2) and testosterone (T) concentrations in Mytilus coruscus. The E2 level ranged from 109.59 to 412.31 pg/g wet weight and from 81.45 to 356.05 pg/g wet weight throughout the year. Furthermore, there was a positive correlation between the E2 level and mean oocyte diameter during the study period, indicating that E2 plays a role in sexual maturation in M. coruscus females and males. Thus, E2 and T may be endogenous modulators in sex determination and in the development and maturation of M. coruscus.