Fig. 4. (A) Heart rate (f_H) and (B) stroke volume (V_s) of resting (•) and swimming () sockeye salmon during an acute temperature increase of 2°C h^–1. Before swimming, a resting value was obtained at 15°C (). At the end of the acute temperature increments, the water velocity for the swimming fish was immediately decreased to the resting value and the temperature was decreased to 15°C over an hour for both groups before a recovery measurement was conducted. All values are means ± s.e.m. Different letters indicate significant differences between temperatures within a group, whereas an asterisk indicates a significant difference between resting and swimming fish at a given temperature.