Reproductive disturbance in a roach (Rutilus rutilus) population affected by cooling water discharge

To analyse a recruitment failure in a roach ( Rutilus rutilus ) population exposed to cooling water from a Swedish nuclear power plant, histopathological examinations were made on female gonads. Several disorders were documented, corresponding to effects previously seen in Lithuanian, Moldavian and Russian heated waters, The relative gonad size (GSI) was generally lower in the exposed population. Oocyte degeneration was observed in about 50% of the females, potentially seriously reducing their reproductive capacity. The gameto- and gonadogeneses also were clearly affected and generally occurred at a faster rate. Sexual maturity was earlier and was accompanied by an increased occurrence of asynchionic gonad and oocyte growth. A normal gonad development should pass through different stages, coupled to the seasons, and the difference between individuals in a population should be small. However, in some exposed fish, the sequence of seasonal development was disturbed and a simultaneous, intensive, growth of sex cells in different stages of development could be seen. An increase of variation in gonad development both within, as well as between, fish thus was documented. Conclusively, the histopathological analysis provided evidence that the observed recruitment deficit could be related to gonad failure.