Toxicity of waters from two streams to early life stages of brown trout (Salmo trutta f. fario L.), tested under semi-field conditions

The development of brown trout (Salmo trutta f. fario L.) in water of two d ifferently polluted streams and in a control situation was monitored in ord er to get insights into the impact of anthropogenic chemical stressors on t he reproductive success of this fish species indigenous to both streams. Th e test streams, situated in the south of Stuttgart, Germany, were the compl exly polluted Korsch stream and the less polluted Krahenbach stream. Bypass systems connected to the streams and a laboratory control system were used for continuous exposure of early brown trout stages shortly after fertilis ation up to the end of the embryonic development. Temperature and oxygen co nditions were standardised in all test series in order to minimise unspecif ic effects. The examined endpoints were: (1) mortality, (2) developmental r ate, (3) time course of hatching, (4) malformations, and (5) growth. A reta rded development, reduced growth rates and higher mortality rates of Korsch stream water exposed embryos indicated an embryotoxic potential for the mo re polluted stream. High infection-related mortality rates of embryos sugge sted the presence of confounding factors also in the less polluted Krahenba ch stream. In parallel to the exposure experiment, physicochemical and limn ochemical parameters as well as concentrations of organic contaminants and heavy metals were monitored. Analytical data confirm the different degrees of pollution of both streams. (C) 2001 Elsevier Science Ltd. All rights res erved.