Abstract

Parasites and pollution are natural and anthropogenic stressors respectively in fishes. A range of biomarkers have been used to assess the sublethal effects of pollutants in fish, but few studies have examined sublethal effects of parasites and pollution in combination. I examined seven biomarkers (pigmented macrophage centres and pigmented macrophage counts in the spleen, pigmented macrophage counts in the liver, white blood cell counts, haematocrit, leucocrit, and condition factor) and parasite abundances in 204 (age 1+ and 2+) spottail shiners ( Notropis hudsonius ) collected at three polluted and two reference localities in the St. Lawrence River, Quebec, Canada. The number of pigmented macrophage centres and pigmented macrophages in the spleen was significantly higher at polluted localities than at reference localities. Seven of the nine species of parasites found in 1+ fish showed significant correlations with biomarkers. More parasites (18 species) but few significant correlations were observed in 2+ fish, indicating that parasite effects are more pronounced in young spottail shiners. A significant negative relationship was observed between condition factor and Neoechinorhynchus rutili (Acanthocephala) in 1+ fish, indicating its potential pathological significance in fish. High abundance of Plagioporus sinitsini (Digenea) was associated with increased spleen macrophage counts and decreased condition factor at polluted localities. Results suggest that counts of spleen macrophages and macrophage centres are good indicators of exposure to pollution in spottail shiners. Furthermore, infection by P. sinitsini in under polluted conditions appears to a greater negative impact on fish health than either stressor alone.