Life through a wider scope: Brook Trout (Salvelinus fontinalis) exhibit similar aerobic scope across a broad temperature range.

Brook Trout (Salvelinus fontinalis) have been widely introduced throughout the world and are often considered as direct competitors with native salmonid species. Metabolic rate is one metric we can examine to improve our understanding of how well fish perform in different habitats, including across temperature gradients, as metabolism can be directly influenced by environmental temperatures in ectotherms. We estimated the standard metabolic rate, maximum metabolic rate, and aerobic scope of lab-reared juvenile Brook Trout (~1 year) using intermittent-flow respirometry across a range of temperatures (5-23 °C) likely experienced in the wild. We included a diurnal temperature cycle of ±1.5 °C for each treatment temperature to simulate temporal variation observed in natural waterbodies. Standard metabolic rate and maximum metabolic rate both increased with acclimation temperature before appearing to plateau around 20 °C, while mass specific aerobic scope was found to increase from a mean of 287.25 ± 13.03 mg O2·kg-1·h-1 at 5 °C to 384.85 ± 13.31 mg O2·kg-1·h-1 at 15 °C before dropping at higher temperatures. Although a slight peak was found at 15 °C, the generally flat thermal performance curve for aerobic scope suggests Brook Trout are capable of adjusting to a relatively wide range of thermal regimes, appearing to be eurythermal, or a thermal generalist, at least for salmonids. The ability of this population to maintain similar physiological performance across a wide range of temperatures may help explain why Brook Trout succeed in a variety of different thermal habitats.