Combined effects of natural and anthropogenic stressors in fish

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Fish are exposed to a variety of stressors in their environment. Like other ectotherms, their internal temperature reflects environmental temperature and hence fluctuates seasonally. Fish are also exposed to contaminants released by industry, cities and agriculture. Metals are a peculiar type of contaminants, because they are also naturally present in the environment and several of them, like iron or copper, are essential for life. However, other metals like cadmium are non-essential, and all metals, essential or not, become toxic at high concentrations. This research program aims at examining the combined effects of variations in temperature and metal exposure on fish condition and health. We will investigate whether the stress induced by elevated temperatures increases their sensitivity to metal contamination, and vice-versa. The program also investigates the limits of tolerance to these stressors for several species of Canadian freshwater fish. ***Most of this research will use controlled laboratory exposures to thermal stress and metals in yellow perch, a North American fish that is widely distributed in Canada and that is abundant in mining areas, as well as fathead minnow and three-spined sticklebacks. In order for laboratory experiments to have an environmental relevance, it is essential to validate laboratory findings in the field. To this end, we will also examine the response of fish to temperature variations and metal exposure in three species of wild fish from the mining area of Rouyn-Noranda, northern Québec. Yellow perch will be sampled in spring, summer and winter in one clean and one metal-contaminated lake and their condition indicators compared with laboratory observations. We will also sample Northern pike, a large predator, and white sucker, a large benthic fish, from the same lakes, in order to provide a global overview of the consequences of these two stressors at different trophic levels. ***The proportion of polyunsaturated fatty acids increases in the cell membranes of cold-acclimated fish and these lipids are more vulnerable to oxidative stress, induced both by metals and heat stress. We will therefore examine the role of membrane composition in the deleterious effects induced by metals and temperature. We will also investigate the functioning of mitochondria, organelles responsible for cellular energy production and highly sensitive to metals and temperature. Finally we will measure indicators of cell performance, including enzymes involved in energy production and antioxidant capacities, indicators of oxidative stress and of energy accumulation, using biochemical and molecular tools. ***Beyond a better understanding of the mechanisms of toxic action of metal contamination in aquatic organisms, this research will enhance our capacity to evaluate the risk for Canadian fish of anthropogenic activities in the context of global warming.