Climate warming is expected to alter distribution patterns of fishes, with temperatures in some systems already approaching the upper thermal tolerance of endemic species (Caissie, 2006). In salmonids, warming water temperatures affects migration (Crossin et al., 2008), smoltification (McCormick et al., 1999), growth and survival (Swansburg et al., 2002). The Miramichi River, located in eastern Canada, is a prominent Atlantic salmon (Salmo salar) river (DFO, 2013) where maximum summer temperatures can reach 27–30°C (Caissie et al., 2014), well beyond the range for optimal growth in juveniles (~15–20°C; Jobling, 1981; Elliott and Hurley, 1997; Jonsson et al., 2001; Elliott and Elliott, 2010). The upper threshold for normal feeding behavior (i.e. 22–24°C; Breau et al., 2011) can be surpassed for as many as 62 days during the spring/summer (Caissie et al., 2012). Peak water temperatures typically occur in conjunction with diel fluctuations of ≤9°C in summer months (our unpublished work). Thus, the Miramichi River is an ideal system for understanding the effects of climate warming on salmon physiology. An appreciation of a fish's physiological capacity to cope with climate-driven environmental stress is emerging as a powerful approach in conservation and management as has been demonstrated for Pacific salmon (Cooke et al., 2012, Muñoz et al., 2014).