The upper thermal tolerance of brook trout Salvelinus fontinalis was estimated using critical thermal maxima (CTmax ) experiments on fish acclimated to temperatures that span the species' thermal range (5-25°C). The CTmax increased with acclimation temperature but plateaued in fish acclimated to 20, 23 and 25°C. Plasma lactate was highest, and the hepato-somatic index (IH ) was lowest at 23 and 25°C, which suggests additional metabolic costs at those acclimation temperatures. The results suggest that there is a sub-lethal threshold between 20 and 23°C, beyond which the fish experience reduced physiological performance.
Keywords: body condition; critical thermal maxima; fish; hepato-somatic index; lactate; osmolality.
© 2020 The Fisheries Society of the British Isles.