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

In this study, we investigated seasonal variations in the concentrations of estradiol‐17β (E 2 ) 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. E 2 and T concentrations were measured by enzyme‐linked immunosorbent assay (ELISA). E 2 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 E 2 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. E 2 andT concentrations were low during the non‐reproductive period extending from July to October. These results suggest that E 2 and T could play a role as endogenous modulators in the reproductive cycle of F. mutica .