Comparison of cisco (Coregonus artedi) aerobic scope and thermal tolerance between two latitudinally-separated populations

The cisco Coregonus artedi is a coldwater fish that is distributed throughout much of Canada and the northern United States, including the Laurentian Great Lakes. Cisco historically supported large commercial fisheries in the Great Lakes during the late 1800s and early 1900s, but many populations declined and never recovered. Restoration efforts focusing on re-establishing cisco in the Great Lakes are underway, but increasing water temperatures may hinder these efforts. Therefore, we examined aerobic scope and thermal tolerance of allopatric cisco populations from different latitudes and habitats to determine if a southern latitude population (Crooked Lake, Indiana, USA) near the southern edge of cisco distribution was better adapted to withstand warmer water temperatures than a northern latitude population (Les Cheneaux Islands, Michigan, USA; Lake Huron). As expected, both stocks demonstrated increases in metabolic rates and absolute aerobic scope with increased temperature. Northern cisco had significantly lower aerobic scope compared to southern cisco at both treatment temperatures of 10 and 13 °C. Both cisco stocks had high thermal tolerances when challenged by temperatures increased to 20 and 23 °C but low tolerances at 26 °C. Cisco thermal tolerances increased with acclimation temperature, but we did not detect a difference in thermal tolerances between northern and southern cisco. Although southern cisco had higher capacity for aerobic metabolism, both stock sources had high thermal tolerances at the upper end of their thermal limits. Therefore, either population would be likely suitable for reintroduction into Great Lakes habitats, even with expected warming in the future.