Stress status of gudgeon (Gobio gobio) from rivers in Switzerland with and without input of sewage treatment plant effluent.

To assess the importance of sewage treatment plant effluents on fish health, we studied gudgeon in two rivers in the Swiss midlands (Canton Lucerne). Both rivers receive pollution from diffuse sources, while one also receives the effluent of a sewage treatment plant. Male and female gudgeon during and outside of the spawning season were compared with respect to reproductive parameters and health status across both rivers as well as upstream and downstream of the STP. Several biomarkers were studied, including cytochrome P4501A, 7-ethoxyresorufin-O-deethylase, plasma vitellogenin, ovotestis, lipid, liver histology, condition factor, gonadosomatic index, splenosomatic index, parasites of spleen and liver, population structure, and species diversity. Gudgeons of both rivers exhibited signs of a moderately impaired health status. By a stepwise backward analysis, the cytochrome P4501A content, the splenosomatic index, and the incidence of parasites in the liver were found to provide the best discrimination of the three sampling sites. Evidence of a significant elevation in response to the sewage treatment plant effluent was found neither in vitellogenin concentration nor in the ovotestis rate. While population structure was analyzed upstream and downstream of the sewage treatment plant, only gudgeons of the latter site revealed a disturbed population structure, most probably caused by a former nitrite discharge.