As well as having a fundamental economic importance, Atlantic cod are very temperature sensitive. As such, we examined the swim physiology of two cod populations from a latitudinal cline, i.e. from the Barents Sea (NEAC) and the German Bight (NSC). Groups of cod were acclimated in excess of 1 year to 4 or 10°C. The extrapolated standard metabolic rates (SMR) showed no significant differences, however a comparison of the Q10s showed that while the NSC can acclimate to warmer temperatures (Q10=1.3), the NEAC could not (Q10=3.1). The active metabolic rate (AMR) was similarly affected by temperature, Q10=2.6 for NEAC and 1.9 for NSC. Because the AMR was also elevated in the 10°C acclimated NEAC, no significant differences were seen in the net aerobic scope, nor the critical swimming speeds, although both were higher in both 10°C acclimated groups than the 4°C acclimated groups. The recovery half-life was significantly longer in the 10°C acclimated NSC compared to 10°C acclimated NEAC, and both 4°C acclimated groups. Despite the long acclimation period, i.e. >1 year, the NEAC appeared to have reduced acclimation capacity when warmed to 10°C. Nevertheless, an uncompensated and thus increased AMR meant aerobic scope and ultimately critical swimming speed were maintained. The increased aerobic capacity in the 10°C acclimated NEAC was also reflected in the faster recovery times. This means that despite a higher metabolic rate when warmed, swimming performance in NEAC is comparable to that of NSC at 10°C. However, questions remain, such as what affect this elevated metabolic cost would have on fecundity, the lethal temperature or hypoxia tolerance?