Upper thermal tolerance of wild-type, domesticated and growth hormone-transgenic coho salmon Oncorhynchus kisutch

In coho salmon Oncorhynchus kisutch, no significant differences in critical thermal maximum (c. 269 degrees C, C-Tmax) were observed among size-matched wild-type, domesticated, growth hormone (GH)-transgenic fish fed to satiation, and GH-transgenic fish on a ration-restricted diet. Instead, GH-transgenic fish fed to satiation had significantly higher maximum heart rate and Arrhenius breakpoint temperature (mean +/- s.e. = 173 +/- 01 degrees C, T-AB). These results provide insight into effects of modified growth rate on temperature tolerance in salmonids, and can be used to assess the potential ecological consequences of GH-transgenic fishes should they enter natural environments with temperatures near their thermal tolerance limits.