Fredagskollokvium: Christine Couturier: The Atlantic salmon in a warmer world

North Atlantic ocean can expect rising water temperatures by the end of the century, and the potential effect of warmer temperatures on the performance of wild Atlantic salmon (Salmo salar) is presently not understood. The difference between resting and maximum oxygen consumption, the aerobic scope, determines how much energy fish can invest into feeding, growth and reproduction. Resting and maximum oxygen consumption rise with temperature at different rates, and beyond the optimal temperature (Topt), further increase in temperature will reduce the aerobic scope. Thus, long before water temperature reaches the critical temperature that is immediately lethal, it will reduce the energy available for feeding, growth and reproduction. A reduced aerobic scope has now been identified as a key factor threatening population survival of fish in a warmer future. Determining the optimal temperature can be achieved easily and efficiently by measuring maximum heart rate. Therefore, in this project we have compared maximum heart rate of two populations more than 4000 km apart, one from northern Norway (Alta, fish experiencing average river temperatures between 0 and 15°C) and the other from France (Dordogne, fish experiencing average river temperatures between 5 and 25°C). Fry were raised at 12 and 20°C for a month after their first feeding and maximum heart rate was determined at temperatures between 12 and 27°C. For both acclimation groups, maximum heart rate increased with temperature and Topt was higher for the warmer acclimated group, but surprisingly, there were no significant differences in maximum heart rate between the two populations before reaching 24°C, indicating a lack of local temperature adaptation and the ability for both populations to face high temperature.