Effects of 2,2',4,4'-tetrabromodipheny ether (BDE-47) on gonadogenesis of the manila clam Ruditapes philippinarum

The reported adverse effects of Polybrominated diphenyl ether (PBDE) congeners on gonadogenesis in fish may also occur in marine bivalves especially the burrowing species such as manila clam Ruditapes philippinarum. In this study, clams were exposed to BDE-47 for 25 days at 0, 0.1 and 1 μg/L. By using the water temperature control method, gonadal maturation from resting to ripe stage were observed successively in both the control and the treatment groups during 25 days. The results showed that exposure to BDE-47 at concentration below 1 μg/L did not delay the gonadogenesis process of the clam R. philippinarum, and no evidence of adverse effects of BDE-47 on clam gonadal histology was observed. However, exposure to 1 μg/L BDE-47 caused significant decreases of haemolymph testosterone levels in both female and male clams at day 5 and day 15. The mRNA expression of 3β-HSD in females exposed to BDE-47 was significantly decreased at day 5, while mRNA expression of 17β-HSD and CYP17 was not significantly changed in either sex. Exposure to BDE-47 also resulted in up-regulation of the mRNA expression of vitellogenin (Vtg) in both sexes and spermatogenesis associated protein 4-homolog (SAP4) in males. These results suggest a potential contribution of BDE-47 to reproductive disruption in the manila clams, especially in males. This study demonstrates the promising utility of water temperature control method in conjunction with histological endpoints and biomarkers such as mRNA levels of Vtg in determining the reproductive disturbances caused by EDCs on bivalves.