Fig. 3

Changes in heart rate (f_H) and related parameters when Atlantic salmon were given a critical swim (U_crit) test (water velocity increment of 0.2 BL s⁻¹). a f_H (in bpm) was measured every 2 min in salmon immediately prior to (resting values) and during the U_crit test. Heart rate variability (HRV, in ms); b was manually calculated from the electrocardiograms and the percentage of ‘good’ quality ECGs (i.e., QI₀); c was calculated by the tag algorithm. Dissimilar lower case letters indicate a significant difference between values, as determined by linear mixed-effects models. These models did not include the swimming speeds of 1.8 and 2.0 BL s⁻¹ due to low sample sizes. The percentage of good quality ECGs did not change significantly with swim speed (P > 0.05). Data are means ± S.E.M.; n = 6–8 except where indicated