Measurements of cardiovascular physiology of the Antarctic fish Pagothenia borchgrevinki and Trematomus bernacchii acclimatized to -1°C and +4°C

Evolutionary theory predicts that specialisation to a narrow set of environmental conditions will lead to a decreased capacity for phenotypes to change in response to environmental variability. This study tested this hypothesis by determining the thermal plasticity of the Antarctic fish Pagothenia borchgrevinki. Fish were acclimated to either -1°C or +4°C for at least 4 weeks. Fish were exercised in a swimming respirometer using a standardised Ucrit measure of performance at their acclimated temperature and at other temperatures at the opposite end of the range they were acclimated to from -1°C up to 8°C. Cardiac output, heart rate and blood pressure was measured from each fish at rest and during stress (exercise and temperature). Samples of tissue (red and white muscle, heart and liver) were collected from all of the fish and analysed for both anaerobic and aerobic enzyme activity to determine if the fish acclimatized to the new temperatures by determining if their biochemical systems have changed. Further tissue samples (blood, plasma, heart, liver, muscle) were collected from freshly caught and acclimated animals. The time course for change (when fish were acclimatized) was determined by sampling fish at a range of times from one day to one month while they were being acclimatized to a change in temperature to determine whether observed changes were specific to survival at these elevated temperature or whether they were simply generalised effects of temperature increase. There is an assumption that maximum oxygen consumption of an organism does not change greatly with temperature change. The maximum oxygen consumption in animals subjected to a stepped increase exercise regime and the rate of recovery following exercise was measured.