| Summary: | Feral perch (Perea fluviatilis L.) and roach (Rutilus rutilus L.) populations, the fish community and experimentally exposed juvenile whitefish (Coregonus lavaretus L. s.l.) were studied in the recipient areas of three pulp and paper mills and at reference areas in the Southern Lake Saimaa, Finland. The mills used elemental chlorine free (ECF) bleaching and activated sludge effluent treatment technologies. The exposure of feral and caged fish to pulp mill effluents, as measured by concentrations of chlorophenolics in the bile and liver EROD activity, was low and almost the same as the reference levels. Nevertheless, resin acid concentrations in the bile of fish near one of the mills were 10-90 times higher compared to the reference points. Reproductive steroid hormones, measured at different reproductive stages, showed that plasma estradiol-17ß and testosterone concentrations were significantly lower in exposed perch and roach during periods of gonadal development. This coincided with a lower gonad size and fecundity in female perch. The gonad size in male perch, as well as the gonad size, egg size, fecundity and plasma and liver cytosol vitellogenin (VTG) in roach, however, remained unchanged. A higher liver size in exposed perch and roach suggests alterations in the metabolic and nutritional status of the fish. However, the body condition and hematological and immunological parameters of exposed fish were not affected. The perch population in the recipient of one of the mills exhibited an abnormal size and age distribution. Spawning behavior, growth and age at maturity of perch and roach was similar between mill and reference areas. The fish communities in the different study areas in the Southern Lake Saimaa were dominated (> 60%) by perch and roach. Biomass and fish densities were highest in the polluted area (5-15 km from the mills) and lowest in the reference area and close (2-5 km) to the mills. The number of species was similar among the areas. Species like bleak and ruffe were typical to the polluted ...
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