Determining the upper thermal tolerance of Athabasca rainbow trout (Oncorhynchus mykiss) across naturally varying stream temperatures in the Athabasca River watershed

Stream temperature is a key driver of physiological function in ectothermic fish, and fish have clear upper and lower limits to thermal habitat use. Stream temperature increases from climate change are a major threat to coldwater taxa like Athabasca rainbow trout (Oncorhynchus mykiss; ARBT), listed as Endangered under Canada’s Species at Risk Act. To better understand their vulnerability to climate change and prioritize recovery locations, ARBT were collected in August 2021 from three streams in the upper Athabasca River, Alberta, Canada, across a gradient of thermal regimes ranging from cold to warm. Individual thermal tolerance was measured using two physiological metrics: agitation temperature (Tag) and critical thermal maxima (CTmax) using a portable streamside laboratory. Tag is a behavioural indicator of a thermal avoidance threshold, whereas CTmax is a physiological response that can be interpreted as the upper thermal limit where long term survival is reduced. Results provide st..., Upper thermal tolerance experiments were conducted in a mobile streamside laboratory trailer to determine CTmax and Tag. Large heating tanks were filled to a predetermined volume with stream water ensuring the experimental starting temperature reflected resident thermal conditions. Throughout the experiment, fish were individually housed in small acrylic chambers with mesh ends (n = 6). Individual chambers functioned to reduce social and physical interactions between study fish while permitting continuous water exchange between the chamber and tank. Water temperature in the tank was controlled by five submersible heaters (TH-0300S titanium heaters, Finnex, Chicago, IL, USA) to gradually increase the temperature at a standardized heating rate of 0.3 °C/min (Becker & Genoway, 1979) for both CTmax and Tag trials, with temperature monitored to ensure an accurate heating rate. Two circulation pumps and air stones were also placed in the tank to ensure uniform water temperature and satura..., , # Determining the upper thermal tolerance of Athabasca rainbow trout (Oncorhynchus mykiss) across naturally varying stream temperatures in the Athabasca River watershed.

[https://doi.org/10.5061/dryad.5qfttdzh5](https://doi.org/10.5061/dryad.5qfttdzh5)

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## Description of the data and file structure

Streamside thermal physiology experiments were conducted on Athabasca Rainbow Trout during July and August 2021 near Hinton, Alberta, Canada. Fish were collected from three streams using electrofishing and transferred to experimental tanks. The water temperature in the tanks was gradually increased at a rate of 0.3°C per minute, while the fish were observed for signs of agitation (Tag) and critical thermal maxima (CTmax). Upon reaching CTmax, the fish were immediately transferred to a colder recovery tank. Genetic fin clips, length, and weight measurements were recorded, and the fish we...