Fig. 3. Examples of on-line venous blood oxygen partial pressure (PVO₂) measurements in the ductus Cuvier of (A,B) cold-acclimated and (C,D) warm-acclimated rainbow trout during the first (habituation) and second (critical speed) swim tests. The incremental increases in water velocity are also shown for reference. The symbols `f' and `b' refer to fighting and burst-and-coast swimming behaviours, respectively, which were visually observed. 1 torr=133.3 Pa.