Brook trout populations vary in the thermal acclimation response of their myotomal muscle: Implications for the impact of climate change.

Cold-water fishes, such as salmonids, face environmental stresses resulting from climate change. We examined the thermal acclimation response of the hatchery-reared versus wild, native brook trout (Salvelinus fontinalis) to explore how the contractile properties and gene expression of their myotomal muscle might shift to mitigate the impact of a warming environment. Hatchery fish were acclimated to three temperatures (4, 10 and 20°C), while wild fish were collected across the seasons grouped by water temperature at time of collection (<6, 10-12 and >16°C). When tested at a common temperature (10°C), maximum escape swimming velocity and contractile properties such as maximum muscle shortening velocity showed a significant thermal acclimation response in both groups of fish. However, other contractile properties, such as twitch time, varied in how each population responded to the thermal environment. These fish also showed changes in the expression of a wide variety of muscle and metabolic genes with elevated temperature, providing a mechanistic foundation for differences in thermal acclimation by each population. These fish showed similar but not identical shifts in muscle function and gene expression with a warming environment, suggesting that wild populations of brook trout may vary in their thermal acclimation response across the range of this cold-water salmonid.