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Understanding how metabolic costs change in relation to increasing temperature under future climate changes is important to predict how ectotherms will be affected across the globe. In fish, whole body respiration is traditionally used to estimate aerobic performance via an organism's minimum and maximum oxygen consumption rates. However, mitochondria play a crucial role in the aerobic cascade and may be a useful surrogate of aerobic performance. To test whether whole body oxygen consumption and mitochondrial capacity are correlated, we estimated whole body metabolic and mitochondrial respiration rates (using permeabilized red muscle fibres) in brook trout (Salvelinus fontinalis (Mitchill, 1814)) at 10, 15, and 20 °C. Standard metabolic rate increased with acclimation temperature, while maximum rates were less sensitive. All mitochondrial respiration rates increased with acclimation temperature, suggesting that red muscle mitochondrial preparations may correlate to the minimal metabolic demands in this species. When expressed as relative rates of electron flow, the red muscle fibres showed no effect of temperature on mitochondrial coupling efficiency. However, there was a pattern of declining capacity to augment respiration via complex II with increasing temperature with a concomitant increase in the capacity of the phosphorylating system relative to maximal rates of mitochondrial electron flow. [ABSTRACT FROM AUTHOR]

The physiology and behaviour of fish are strongly affected by ambient water temperature. Physiological traits related to metabolism, such as aerobic scope (AS), can be measured across temperature gradients, and the resulting performance curve reflects the thermal niche that fish can occupy. We measured AS of westslope cutthroat trout (Oncorhynchus clarkii lewisi) at 5, 10, 15, 20, and 22 °C and compared temperature preference (Tpref) of the species with non-native brook trout (Salvelinus fontinalis), brown trout (Salmo trutta), and rainbow trout (Oncorhynchus mykiss). Intermittent-flow respirometry experiments demonstrated that metabolic performance of westslope cutthroat trout was optimal at ∼15 °C and decreased substantially beyond this temperature, until lethal temperatures at ∼25 °C. Adjusted Tpref across species were comparatively high, ranging from 17.8 to 19.9 °C, with the highest Tpref observed for westslope cutthroat trout. Results suggest that although westslope cutthroat trout is considered a cold-water species, they do not prefer or perform as well in cold water (≤10 °C) and thus can occupy a warmer thermal niche than previously thought. The metabolic performance curve (AS) can be used to develop species‐specific thermal criteria to delineate important thermal habitats and guide conservation and recovery actions for westslope cutthroat trout. [ABSTRACT FROM AUTHOR]

Fisheries and Oceans Canada's Species at Risk Program provides protection of the habitat necessary for the survival or recovery of listed freshwater fishes and mussels. It is well documented that the riparian zone is essential for the maintenance of freshwater aquatic habitats, fishes, and mussels. Despite this extensive body of literature, riparian features are not consistently included as Critical Habitat for listed freshwater fishes and mussels. An evidence based approach was required to guide the identification of features in the riparian zone as Critical Habitat. Riparian Critical Habitat are riparian features that: maintain the quality of aquatic features identified as Critical Habitat, and are directly used by fishes and mussels. We performed a literature review to determine the relevant riparian features, and the processes by which they affect aquatic features and water quality attributes. From these literature reviews we identified seven main processes by which riparian features affect aquatic features and water quality attributes: erosion, filtration, infiltration, isolation, meandering, shading, and subsidization. In addition, we identified riparian features that may directly support freshwater fishes and mussels' functions depending on their life history. Meta-analyses, reviews, and primary research articles were assessed to provide some guidance on the extent of riparian habitat required to support these seven processes. We outlined the current state of the literature regarding the extent of habitat required, and denoted where more empirical evidence is required. The dependencies of each process on attributes of the floodplain and other important considerations were summarised and can be consulted to determine what riparian features should be protected as Critical Habitat for a listed species. We have included additional resources to aid in the application of this guidance when defining the geographical area to be protected. Finally, five case-studies were used to provide an example of how practitioners may apply the guidance provided here to determine riparian Critical Habitat for a listed species. [ABSTRACT FROM AUTHOR]

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. • Estimated metabolic rates of Brook Trout across a range of temperatures (5–23 °C). • Acclimation temperatures included a 3 °C daily diurnal temperature cycle. • Brook Trout aerobic scope peaked around 15 °C. • Standard metabolic rate and maximum metabolic rate reached a plateau around 20 °C. • Brook Trout appear to be a thermal generalist salmonid species. [ABSTRACT FROM AUTHOR]

Chemically induced anaesthesia is currently the only approved method for anaesthetising fish for sampling and surgical procedures by many organizations, including the Canadian Council on Animal Care, Health Canada, and the U.S. Food and Drug Administration (FDA). Although MS-222 (Tricaine-S) performs well, the long chemical withdrawal time makes it a poor choice for field-based research where fish cannot be held very long, especially in areas where commercial, subsistence or recreational fisheries occur. The lack of approved anaesthetic options for field research is mainly due to a lack of research on the suitability of alternatives, particularly for surgery. In the present study, juvenile brook trout (Salvelinus fontinalis) were subjected to a handling stressor or surgical stressor (tag implantation) using one of three anaesthetics: MS-222, AQUI-S®, and electro-immobilization. Indicators of stress (blood glucose and plasma cortisol) were measured over five time points (0 h, 1 h, 4 h, 24 h, 1 week post-stressor). The results from this study suggest some time-specific differences in stress levels between anaesthetics; however, there was limited evidence to suggest differences in the efficacy of the anaesthetic methods at mediating stress levels in brook trout. Thus, both AQUI-S® and electro-immobilization may provide suitable alternatives to MS-222 for field research. • We compared three anaesthetics and their ability to reduce stress in brook trout from handling and surgery events. • MS-222, electro-immobilization and AQUI-S® reduced stress from handling and surgery events similarly in brook trout. • No significant difference in stress levels occurred in brook trout across handling and surgery treatments. • Overall profiles of plasma cortisol and blood glucose were similar across anaesthetics one week following the stress event. • Electro-immobilization had fastest sedation and recovery times of all three anaesthetics tested. [ABSTRACT FROM AUTHOR]