Our measured physiological responses to thermal cycling were strikingly similar amongst the treatments and could be indicative of partial acclimation to increased temperatures caused by a slow ramping rate, or could suggest phenotypic plasticity to cope with thermal variability (Schulte et al., 2011; McBryan et al., 2013; Anttila et al., 2014). Metabolic stress in Atlantic salmon occurs at temperatures between 22°C and 24°C (Breau et al., 2011) demonstrating a limited ability to tolerate temperatures >28°C (Garside, 1973; Elliott, 1991), enduring 33°C only in acute circumstances (Elliott and Elliott, 1995). It is possible that genetic makeup and thermal history, specifically the frequency that these upper thermal thresholds are surpassed, may play a larger role in the metabolic and cellular status of juvenile salmon, while nighttime temperature may have little influence on a fish's ability to re-establish basal cellular and metabolic conditions. Wehrly et al. (2007) determined maximum temperature tolerance to be a function of time in two trout species, Salvelinus fontinalis and Salmo trutta, where prolonged warm periods negatively influenced upper thermal tolerance limits. Furthermore, in chronically warmed European perch (Perca fluviatilis), Sandblom et al. (2016) determined that, despite cardiorespiratory plasticity to deal with a warmer resting condition, the upper thermal limit remained relatively rigid in both cold and warm adapted fish, consequently reducing the available ‘thermal buffer’.