Interactions between parasites and pollutants in yellow perch (Perca flavescens) in the St. Lawrence River, Canada: implications for resistance and tolerance to parasites.

Parasites were examined in yellow perch, Perca flavescens (Mitchill, 1814), from four localities ranging in degree of pollution in the St. Lawrence River, Quebec, Canada, to examine the effects of the most prevalent parasite species on expression of biomarkers of oxidative stress. Various biomarkers appeared to be affected by the infection levels of Apophallus brevis Ransom, 1920 and genus Diplostomum von Nordmann, 1832. For certain biomarkers, interactions between infection level and pollution type were detected for A. brevis, Diplostomum spp., and genus Ichthyocotylurus Odening, 1969. Activity of glutathione reductase in gill tissue decreased with increasing numbers of A. brevis, but only at the two most polluted localities. Catalase activity in kidney increased with numbers of Diplostomum spp. at the polluted localities, but not at the two least contaminated sites. Results suggest that parasites may affect expression of biomarkers of pollution and that pathogenicity of parasites may be enhanced under p...