High estradiol exposure disrupts the reproductive cycle of the clam Ruditapes decussatus in a sex-specific way.

Bivalve species may be susceptible to environmental estrogenic compounds including estradiol (E). However, they are able to biotransform the hormone quite readily and inactivate its estrogenic action. To study the long-term effects of elevated free E tissue levels, we transiently exceeded the biotransformation capacity of the clam Ruditapes decussatus by exposing them with high E concentrations (400 ng/L) and subsequently study the consequences on gametogenesis during the following reproductive cycle. Exposure to 400 ngE/L led to a significant increase in tissue free E levels, which reached 10-50 ng EEq/gww. No deleterious effect on gonado-somatic index (GSI), condition index (CI), or ability to respond to the stress on stress test could be detected after a month of exposure, suggesting the absence of negative effects on the clam's health. However, a marked increase in gametogenesis could be observed in both sexes during the exposure. Subsequent transplantation of the clams in the field allowed the normal development of the male clams and maturation of the gonads without any detrimental effect observed after 4 months. In contrast, in early July, all female clams formerly exposed to E showed lower health status, and only ovaries with atretic oocytes while all control and indigenous females were normal and mature. These results show a sex-specific effect of high E exposure and suggest either a direct or indirect role for E in R. decussatus' reproduction.