Abstract
Investigations on the fish fauna have been performed at four thermal power plants in Sweden situated on Lake Mälaren, the Baltic, the Sound and the Kattegatt. The results illustrate effects of thermal discharge in various salinities, from fresh water to above 20‰. The presentation is based on material from several years of test fishing with gill nets and fyke nets. The most common species have been classified as warm- or cold-water fishes on the basis of the catch/temperature relationship. The reactions towards the cooling-water mainly correspond to this grouping. Exceptions due to special hydrographic conditions and to the supply of food are discussed. Shallow bottoms in freshwaters and at the Baltic coast are massively dominated by warm-water species of freshwater origin, while marine cold-water fishes hold a strong position in the higher salinities of the Sound and the coast of the Kattegatt. The effects of thermal discharge upon the species composition are thus demonstrated to increase with the salinity.
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