Cardiorespiratory responses in an Antarctic fish suggest limited capacity for thermal acclimation

Abstract

Polar fishes are at high risk from increasing seawater temperatures. Characterising the physiological responses to such changes may both clarify mechanisms that permit life under extreme conditions, and identify limitations in the response to continued global warming. We hypothesised that Notothenia coriiceps would show physiological compensation after an acute exposure to 5°C, and following 6wk warm acclimation, compared to ambient temperature (0°C). However, initial tachycardia (22.4±2.8 vs. 12.8±1.1min−1; P<0.01) was not reversed by acclimation (21.0±1.9min−1). Hyperventilation (45.5±3.1 vs. 21.4±2.4min−1; P<0.001) showed a modest reduction (38.0±2.9min−1; P<0.05), while resting oxygen consumption (0.52±0.08mmol.kg−1.h−1) was acutely increased at 5°C (1.07±0.10mmol.kg−1.h−1; P<0.001) but unchanged with acclimation. Autonomic blockade showed initial responses were mainly of vagal origin, with little subsequent withdrawal or recovery in long-term heart rate variability after 6wk. Given the limited cardiorespiratory capacity to withstand sustained warming, effective physiological compensation likely requires a more prolonged acclimation period.