Temperature Effects on Swimming Performance, Oxygen Consumption, and Skeletal Muscle Metabolic Phenotype in Amargosa River Pupfish, Cyprinodon nevadensis amargosae.

AbstractClimate change is raising temperatures in aquatic habitats and shifting the frequency and severity of precipitation events. In fishes, metabolic demands increase under warmer conditions, which may limit the ability of fishes to survive the physical and metabolic demands of high-water flow events if extreme rainfall occurs during periods of high temperature. Here, we investigated how temperature affected the swimming performance, aerobic metabolism, and skeletal muscle phenotype of Amargosa River pupfish (Cyprinodon nevadensis amargosae) to explore how warmer temperatures may reduce the ability of pupfish to cope with fast-moving water. Adult pupfish were acclimated to 16°C, 27.5°C, or 35°C for 63-114 d, after which their swimming performance and metabolic rates were assessed using an intermittent swim-tunnel respirometry system. The critical swimming speed of pupfish increased from 7.9 body lengths (BL) s-1 at 16°C to 9.8 BL s-1 at 27.5°C but declined to 3.8 BL s-1 at 35°C. Paralleling those differences in swimming performance, maximum metabolic rate and aerobic scope were both lower at 35°C. Those differences in rates of oxygen consumption and swimming performance were accompanied by a shift in skeletal muscle metabolic phenotype, with muscle from pupfish at 35°C having reduced mitochondrial density, diminished citrate synthase activity, and ∼65%-80% reductions in relative messenger RNA abundances for citrate synthase and mitochondrion genes atpase6/8 and cox2. These results indicate that pupfish subjected to elevated temperatures experience reductions in skeletal muscle aerobic capacity and swimming performance, which may make these fish more vulnerable to fast-moving waters such as flash floods if those events occur at times of elevated temperature.