Combined effects of natural and anthropogenic stressors in fish

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Canada is exceptionally rich in freshwater resources but human activities impose serious threats to the health of these fragile ecosystems. For instance, mining and smelting operations have significantly contributed to the increase in metal concentrations in water, soils and biota. Fish are particularly vulnerable to environmental contamination since, in addition to direct toxic effects, they integrate effects on other levels of the food web. Further, organisms from contaminated environments are rarely exposed to single contaminants but are typically exposed to complex mixtures in addition to other, natural, sources of stress like high temperatures, hypoxia or dietary restrictions. The long-term objective of this program is to elucidate the metabolic consequences of natural stressors (heat, hypoxia and dietary restriction) and metal contaminants individually and combined in Canadian freshwater fish under environmentally realistic conditions. Specifically, we will examine interspecific differences in metal toxicity and the synergistic and antagonistic effects of natural stressors and metal contaminants on the physiological performance of fish. To this end, fish will be exposed in the laboratory to metals and natural stressors combined. The metabolic response to these stressors will be examined by measuring the activity of key enzymes of aerobic and anabolic pathways, mitochondrial metabolism, oxidative stress, gene transcription levels, cell membrane phospholipid fatty acid polyunsaturation and more general responses like growth rate and accumulation of energy reserves. Field studies will also be carried out to characterize interspecific differences in metal accumulation and toxicity and natural variations in metabolic capacities of wild fish. Ultimately, this research will improve our understanding of the mechanisms of metal toxicity in freshwater organisms and of the additional impacts of natural stressors. This information is essential to improve our ability to develop sound approaches for the protection of our freshwater ecosystems.