Changes in the structure of fish assemblages in a river used for energy production

The fishes in the River Jihlava (a tributary of the River Svratka, Danube d rainage basin, Czech Republic) have been monitored over the past 26 years. The objective of this monitoring has been to determine the effects of the c onstruction and operation of an energy operating complex. This complex is c omposed of two hydroenergetic reservoirs at Dalesice and Mohelno (completed in 1977) and an adjacent nuclear power plant at Dukovany (power generation started in 1985), water is pumped from the reservoir at Mohelno to supply cooling water for the nuclear power plant. The operation of this combined h ydro and nuclear power system has led to substantial changes in the morphol ogical, hydrological, hydrochemical and hydrobiological characteristics of the former riverine habitats. These habitat changes have been followed by c onsiderable changes in the composition of the fish assemblage. In the river downstream of the reservoirs, the former fish community, which was dominat ed by the barbel (Barbus barbus), has been replaced by a trout (Salmo trutt a m. fario) community. In the Dalesice reservoir, limnophilic species gener ally replaced rheophilic species. Both of these habitats are now highly val ued for their sport fisheries. Copyright (C) 1999 John Wiley & Sons, Ltd.