CTMax tests were performed on 9–11 salmon parr at each of three Tmin time points (between 04:00 and 09:00); to establish an initial pre-thermal stress value (24 h), the effect of a singular thermal cycle (60 h), and of multiple heat cycles (120 h; Fig. 1B). Prior to testing, fish were transported to a plastic CTMax experimental chamber (40 × 13.5 × 11 cm) with a clear Plexiglas® lid. Chambers contained an aerated water flow of 4 L min−1 and had an initial water temperature matching that of the experimental procedure. Once the fish was in the chamber, water temperature was increased acutely at a rate 0.32 ± 0.002°C min−1 (mean ± SEM; Becker and Genoway, 1979) until fish lost equilibrium. DO and temperature were measured at 1-min intervals; DO saturation remained >72% in all trials.