Estradiol-17beta and testosterone concentrations in male and female Mya arenaria (Mollusca bivalvia) during the reproductive cycle.

Perturbation of the reproductive cycle as well as vitellin-like protein synthesis have already been reported in Mya arenaria sampled in contaminated areas of the St. Lawrence maritime estuary (Québec, Canada). To assess the potential role of endocrine disruptors in modulating the reproductive cycle in clams, the role of sex steroids has to be clarified. We determined the levels of estradiol-17beta and testosterone during the reproductive cycle in female and male M. arenaria. Both steroids were measured by ELISA in the gonads and no differences in steroid profiles appeared between sexes. Estrogen levels varied between 150 and 400 pg g(-1) wet weight over gametogenesis and were near 10 times higher than testosterone levels. Results showed transient increases of both steroids at the onset of vitellogenesis in females and during the spawning stage in both sexes. These findings indicate that these hormones could have a role as endogenous modulators of gametogenesis. Further studies are, however, needed to describe the pathway of steroid synthesis in clam gonad and elucidate steroid involvement in controlling gametogenesis and as well as their relationship with neurohormones since these latter are required to promote sexual maturation.