Fig. 2. Mean venous blood oxygen partial pressure (PVO₂) measurements in the ductus Cuvier for cold-acclimated and warm-acclimated rainbow trout during graded exercise. Values were derived from periods of steady-state swimming at each velocity increment. To permit comparisons between the cold- and warm-acclimated fish, swimming velocity is expressed as a percentage of the critical swimming speed (%U_crit). Horizontal and vertical bars indicate the S.E.M. Dissimilar letters represent statistical difference within a swim. Values without letters were not included in the repeated-measures analysis of variance (ANOVA). Asterisks represent significant difference between the acclimation temperatures at similar %U_crit. The inset presents the data for the first (habituation) swim. 1 torr=133.3 Pa.