Temperature response in the physiology and growth of lake trout strains stocked in the Laurentian Great Lakes

Fish stocking programs designed for species rehabilitation aim to match the strains being stocked with the environments the fish will inhabit. The ability of different lake trout Salvelinus namaycush populations to adjust their physiological performance over a broad range of environmental conditions will be advantageous as water temperatures rise with climate warming. This study compares the adaptive physiological potential of 6 strains of lake trout stocked within the Laurentian Great Lakes by comparing growth, metabolic and cardiovascular performance, and organ-system tradeoffs across a temperature gradient. Using a common garden design, lake trout were raised from the embryonic stage until 2 years of age, when they were acclimated to temperatures of 8, 11, 15 and 19 degrees C before undergoing experiments to test their metabolic performance. For all strains, growth rates showed a dome-shaped response with temperature, peaking at 11 degrees C and reaching negative rates at 19 degrees C. For 5 of 6 strains, metabolic rates increased while in all strains cardiovascular performance declined with increasing temperature. Higher metabolic rates at higher temperatures generally came at the cost of slower growth, less investment into gastrointestinal mass, and reduced cardiovascular fitness and investment. Importantly, though, the Seneca strain was unique by showing a reduction of aerobic scope at the highest temperature, possibly indicating increased costs as temperature rises in this smaller-sized, potentially slower pace-of-life strain. However, the overall low interpopulation variability in our study suggests limited diversity in the physiological responses to temperature in strains stocked across the Great Lakes basin. (C) 2020 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.