Estradiol‐17β and testosterone levels in the cockle Fulvia mutica during the annual reproductive cycle

Abstract

In this study, we investigated seasonal variations in the concentrations of estradiol‐17β (E2) and testosterone (T) in the gonad of the cockle Fulvia mutica from March 2004 to February 2005 in relation to the reproductive cycle. Histological data showed that F. mutica is a hermaphrodite bivalve species, and gametogenesis took place during winter‐spring (November‐April) and spawning occurred in summer (May‐June) when water temperature was higher. E2 and T concentrations were measured by enzyme‐linked immunosorbent assay (ELISA). E2 concentrations varied between 7.27 and 32.63 pg/g wet weight and T concentrations ranged from 22.83 to 77.15 pg/g wet weight throughout the year. Both steroids exhibited a similar annual pattern that correlated with the reproductive cycle. The two peaks of E2 and T concentrations in November and May‐June occurred at critical moments of the F mutica reproductive cycle: the onsets of gametogenesis and of the spawning period. E2 andT concentrations were low during the non‐reproductive period extending from July to October. These results suggest that E2and T could play a role as endogenous modulators in the reproductive cycle of F. mutica.