The effects of ontogeny in variable temperature and flow waters on the locomotor physiology and morphology of Icelandic arctic charr (Salvelinus alpinus).

Climate change is causing increases in water temperature, flow and their variability in many freshwaters. Predicting fish futures will require knowing how they respond to variations in temperature and flow. This study tested the null hypothesis that locomotor physiology and morphology of Arctic charr are independent of the temperature and flow of water experienced during ontogeny. We raised cultured charr from hatch under a 2 X 2 matrix of flow (3 cm s-1 &15 cm s-1) and temperature (5°C and 13°C) in the laboratory. Fish were compared for sprinting performance (Usprint), swimming kinematics and performance during a constant acceleration swimming test (Ucat) and oxygen consumption before and after the Ucat test. We then captured wild charr from similar temperature environments in Iceland to compare with the laboratory fish. Fish performance in the Ucat test was significantly better at 13°C than at 5°C with an apparent Q10 of 1.3. The effect of rearing flow was noticeable in the metabolic support of swimming; fish reared under low flow at 5°C used more oxygen when swimming at low speed and were slower to recover metabolically from exhaustive swimming. Otherwise, oxygen consumption after exhaustive exercise was fairly uniform across treatments. Freshly-caught wild fish were better sprinters than laboratory fish at both temperatures, recovered faster from the Ucat test at 13°C and were more thermally tolerant. Geometric morphometrics easily separated the shape of wild fish from cultured fish and flow, but not temperature, during ontogeny influenced morphology of cultured fish.