Der Fisch - wie lässt er sich als Indikator für die Qualität seiner Umwelt einsetzen?

In this article, examples are presented for which questions fish can be successfully used as bioindicators. Bioindicators are organisms, which react as sentinels on environmental changes. To decide which parameters have to be selected to best describe such influences, it has to be considered that stressors, which affect the body often have their initial effects at the molecular level. The resulting interactions affect the next higher level in the biological organization, namely the cells, organs and finally the organism or population. Molecular effects are thus expected to be most sensitive and provide the earliest indication. However, their ecological relevance is mostly low since many molecular effects are abolished by repair and protective mechanisms of the organism.A decline of fish populations together with an obviously increasing impairment of fish health was observed in numerous European river systems for years. In Switzerland, the trout catches decreased more than 40 per cent in the last decades.The aim of the study was to compile a set of parameters which cover the extent of changes in fish under adverse conditions and allow to narrow down the causing stressors.Among the molecular markers, stress or heat shock proteins are discussed to be useful for determining the impact of environmental stress. These proteins are involved in the protection of cells from stressor-induced damage, either in form of an adaptive response to prevent from danger or as a response to repair or remove stressor-induced damage. We tested tissue- and cell-specific differences in trout - these have to be known before a broad use in biomonitoring studies can be recommended. A transient increase of the temperature for two hours was sufficient to raise the amount of stress protein HSP 70 in both, gill and skin. Whereas in skin the level remained elevated for two days of recovery, the protein amount decreased rapidly in the gill.Metallothionein, a biomarker of exposure and toxicity of heavy metals has been detected in the gills of brown and rainbow trout. A very prominent labeling of the ion-transporting chloride cells was found after exposure to diluted sewage plant effluents. No significant increase was observed after exposure to river water 8 km further downstream of the sewage plants indicating a decreasing pollution and threat of the trout in this river due to heavy metals. The observed decline in population density is most likely due to other reasons in this river system. Reproductive failure in wildlife attracted considerable attention in the last years. Therefore, we investigated the situation in fish in Switzerland. To detect disturbances in the reproductive system of fish, vitellogenin can be used as a sensitive and specific biomarker. This yolk protein is synthesized in the liver of female mature fish, but can be induced by estrogen or estrogen- like substances in juvenile and male fish as well. Downstream of four out of 36 sewage treatment plants we observed male fish with vitellogenin in their livers. This indicates the presence of hormones or estrogen-like substances in the river water or effluent and has to be further investigated. In laboratory experiments, we showed that one of the estrogen-like substances, nonylphenol (a metabolite of alkylphenol ethoxylates, used in dyes, plastics and industrial cleaning products) induced alterations in the granulation pattern of skin mucous cells and in the surface of gill chloride cells.In the river Alte Aare, low fish populations and health problems were observed for many years. One possible reason is the insufficient water quality, which may be due, among others, by waste water released by a sewage treatment plant. Trout were investigated after exposure with and without addition of sewage effluents. A broad set of parameters was studied. High concentrations of nitrite, ammonia, pesticides and further possibly harmful compounds were detected. Trout suffered high mortalities, pathological changes of liver, kidney, skin and gill, and blood chemistry parameters, and displayed a high abundance of parasites as well as of pathogenic bacteria. We concluded that the combination of several adverse factors, including high water temperatures in the summer is responsible for the observed effects. An interdisciplinary workshop comprising the experience of many experts who worked at this river system for years was the basis for a synthesis report, which included recommendations for measures.In addition to the mentioned studies carried out mostly in the field, approaches are necessary which focus even more strongly on the mechanisms and evaluate the direct response of biomarkers to the environmental conditions than is possible in the whole animal system. Further, we wanted to reduce the number of fish necessary for monitoring and ecotoxicological studies.