Exposure of juvenile roach (Rutilus rutilus) to treated sewage effluent induces dose-dependent and persistent disruption in gonadal duct development.

Wild roach (Rutilus rutilus) have been found with intersex gonads in rivers throughout the United Kingdom. The incidence of intersexuality is strongly correlated with discharges of estrogenic treated sewage effluent into those rivers, and this has led to the hypothesis that estrogenic chemicals in effluents are feminizing wild male fish. In this study, early-life stage roach (50 days post hatch, dph) were exposed for 150 days to a graded concentration (0%, 12.5%, 25%, 50%, and 100%) of treated sewage (primarily domestic) effluent to examine the effects of exposure on sexual differentiation and development. Measurement of steroid estrogens and alkylphenolic chemicals in the effluent and a resulting dose-dependent induction of vitellogenin (VTG; a female-specific, estrogen-dependent plasma protein) confirmed that the fish had been exposed and responded to "estrogen" in the effluent. Exposure to treated sewage effluent induced feminization of the reproductive ducts in "male" roach in a dose-dependent manner (in full-strength effluent, 100% of the fish had feminized ducts), indicating that the disruption of the gonad ducts seen in wild roach is the result of exposure to treated sewage effluents during early-life stages. There were no effects of treated sewage effluent exposure on germ cell development; therefore, no oocytes occurred in the testes of the feminized male roach. Subsequent, depuration of the effluent exposed fish in "clean" water for 150 days resulted in a reduction in plasma VTG but no alteration of the feminized ducts, indicating that the effect of the treated sewage effluent on reproductive duct development was permanent. The causality of oocytes in the testes of wild male roach therefore remains to be elucidated.