The effect of warm discharge waters of a power plant on the occurrence of parasitic Metazoa in freshwater bream, Abramis brama (L.)

One of the environmental factors affecting freshwater ecosystems is thermal pollution. The aim of the presented study was to determine whether the Dolna Odra Power Plant in north-western Poland is capable of altering the parasite fauna of bream, Abramis brama. To compare the affected and non-affected fish we collected a total of 615 bream from three sites: the warm-water canal; river below the canal; and the river, above the power plant. The latter was treated as the ambient-temperature reference site. The waters in the discharge canal were by 6-10 degrees C warmer than the waters from the reference site. The fish from the three sites yielded 21,22, and 23 parasite species, respectively. Differences were observed in the prevalence of particular species as well as other specific parameters. For example copepod Ergasilus sieboldi from the site below the warm-water canal was three times more prevalent than in the canal itself. A similar trend was observed for monogenean Diplozoon paradoxum showing a two-fold difference. Surprisingly, glochidia Unionidae gen. spp. were more prevalent at the warm-water site. The parasite communities and their infection parameters in bream collected above the power plant were similar to those observed in the river below. The observed differences suggest that the effect of thermal pollution caused by the Dolna Odra Power Plant on the parasite fauna of bream was not as extensive as expected.