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.

Metabolic rate and critical thermal maximum CTmax estimates for westslope cutthroat trout, Oncorhynchus clarkii lewisi.

Global warming is changing the thermal habitat of cold-water freshwater fishes, which can lead to decreased fitness and survival and cause shifts in species distributions. The Alberta population of westslope cutthroat trout (Oncorhynchus clarkii lewisi) is listed as 'Threatened' under the Canadian Species at Risk Act. The major threats to the species are the alteration in habitat and water flow, competition and hybridization with non-native trout species and climate change. Here, we conducted (i) intermittent-flow respirometry experiments with adult native westslope cutthroat trout and non-native rainbow trout (Oncorhynchus mykiss) and (ii) critical thermal maximum experiments (CTmax ) with adult westslope cutthroat trout to obtain valuable input data for species distribution models. For both species, standard metabolic rate (SMR) was lower at 10°C compared to 15°C and westslope cutthroat trout had higher SMR than rainbow trout. Although there were inter-specific differences in SMR, forced aerobic scope (using a standardized chase protocol) was different at 10°C, but no significant differences were observed at 15°C because of relative smaller differences in maximum metabolic rate between the species. CTmax of westslope cutthroat trout acclimated to 10°C was 27.0 ± 0.8°C and agitation temperature was 25.2 ± 1.0°C. The results from this study will inform and parametrize cumulative effects assessments and bioenergetics habitat modelling for the recovery planning of the species.

Development and testing of a simple field-based intermittent-flow respirometry system for riverine fishes.

By understanding range-wide intraspecific variation in metabolic rate we can better understand how organisms have adapted to their environment. However, methods to quantify metabolic rate of fishes from remote areas or those that cannot be brought back to the laboratory because of imperilment status are lacking. Consequently, practical and reliable field-based methods are needed. To address this need, we developed a simple yet robust intermittent-flow respirometry system, adapted from a design commonly used in the laboratory that is readily suited for field use. Standard metabolic rate (SMR), maximum metabolic rate (MMR) and aerobic scope (AS) estimates were obtained from juvenile lake trout (Salvelinus namaycush) and brook trout (Salvelinus fontinalis) using both field- and laboratory-based systems. Whole-fish SMR, MMR and AS estimates from the field and laboratory methods did not differ from one another (ANCOVA and LMM: all P > 0.05) for either species and were comparable to estimates previously reported. Our field setup is a simpler system than the conventional laboratory-based system that requires less power and equipment to operate, yet still offers users the ability to: (1) acclimate fish to the respirometry chamber; (2) measure oxygen consumption during a shorter period (1 h), which yield metabolic rate estimates comparable to systems that take measurements over longer periods; and (3) take repeated oxygen consumption measurements with manual user-defined flush and measurement phase routines. Developing practical and reliable field respirometry methods, as demonstrated here, is important if we wish to improve our ability to predict how imperiled species will respond to changes in their environment. Such knowledge is critical for informing conservation strategies.