Critical Thermal Maxima of Wild and Domestic Strains of Trout

Abstract

The slow growth and high mortality of hatchery-reared brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss during summer in a stream that supported wild brown trout prompted us to compare the critical thermal maxima (CTMax) of wild and domestic strains of brown trout, brook trout Salvelinus fontinalis, and rainbow trout. First, we tested the effects of electrofishing exposures on the CTMax of hatchery-reared brown trout. We compared the CTMax of three domestic strains of brown trout to determine possible genetic influences on upper temperature tolerance and then collected wild trout with electrofishing gear and compared their CTMax to that of the hatchery strains. There was no significant effect of electrical shocks on the CTMax of hatchery-reared brown trout, and CTMax differed significantly among these three domestic strains. Wild strains of all three species had significantly higher CTMax than did domestic strains; differences ranged from 0.5°C to 1.6°C. We tentatively conclude that differences in CTMax between wild and domestic strains are genetically based.