Metabolic rate and critical thermal maximumCTmaxestimates for westslope cutthroat trout,Oncorhynchus clarkii lewisi

Abstract

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.

Physiological responses to acute warming at the agitation temperature in a temperate shark

“…As such, the agitation temperature is interpreted as a behavioural response to thermal stress. Since this study, numerous others have quantified the agitation temperature and demonstrated that it occurs before CT max (Enders and Durhack, 2022;Kochhann et al, 2021;Turko et al, 2020;Wells et al, 2016) and is responsive to temperature acclimation and acute hypoxia (Firth et al, 2021;McDonnell et al, 2019McDonnell et al, , 2021Potts et al, 2021). Because the agitation has been shown to be sensitive to acute hypoxia, studies have suggested that cardiorespiratory performance may set the agitation temperature (McDonnell et al, 2021;Potts et al, 2021).…”

“…Definitions of behavioural endpoints for an agitation temperature are often specific to the experimental arena and study species. For consistency within the literature, our definition of the agitation temperature is similar to a study in cutthroat trout (Oncorhynchus clarkia lewisi) that were confined within respirometry chambers (Enders and Durhack, 2022). CT max was recorded as the temperature at which dogfish exhibited muscle spasms, as indicated by rapid, lateral convulsions originating from the animal's trunk (Bouyoucos et al, 2020).…”

“…McDonnell and Chapman, 2015;Wells et al, 2016) but not all studies that quantify an agitation temperature (e.g. Enders and Durhack, 2022;Turko et al, 2020). As such, determination of agitation and CT max was subjective, blinding was not possible and observer bias could not be accounted for experimentally.…”

“…As such, determination of agitation and CT max was subjective, blinding was not possible and observer bias could not be accounted for experimentally. The agitation temperature occurs before CT max (Enders and Durhack, 2022;McDonnell and Chapman, 2015), therefore, trials were terminated upon dogfish achieving CT max . Upon termination of a trial, individual dogfish were tagged through the first dorsal fin with a numbered anchor tag for identification and were rapidly returned to their holding tank for recovery.…”

Local environments, not invasive hybridization, influence cardiac performance of native trout under acute thermal stress

“…In particular, salmonid populations that have evolved in warm climate regimes exhibit higher critical thermal maxima (CT max ), maximum heart rate ( f h,max or “MaxHR”), and aerobic scope under stressful water temperatures than typical populations from cooler environments (e.g., Chen, Farrell, Matala, & Narum, 2018 ). While cardiac performance and thermal tolerance can be altered by acclimation temperatures in both rainbow trout (redband; O. mykiss gairdneri ; Chen, Farrell, Matala, & Narum, 2018 ) and westslope cutthroat trout (Enders & Durhack, 2022 )—which reflects plasticity within each species—evidence also exists for local adaptation in these traits among populations from distinct climates (e.g., Chen, Farrell, Matala, Hoffman, & Narum, 2018 ). A broader understanding of the physiological effects of hybridization and the potential role of local environmental conditions is needed to inform climate adaptation strategies and to protect native species threatened by invasive hybridization under future climate change.…”