Approximately 15% of a population of the cryopelagic nototheniid fish Pagothenia borchgrevinki, found constantly swimming immediately beneath the annual fast ice, in McMudro Sound, Ross Sea, Antarctica, was affected by X-cell gill disease. This disease affected blood flow through the gill lamellae, and this in turn affected oxygen uptake. Exercise caused increases in heart rate and ventral aortic blood pressure. Heart rate increased from 15·1 ± 1·55 to 23·1 ± 0·93 beats min−1 in healthy fish, with a similar increase (to 24·6 ± 0·26 beats min−1) in X-cell-affected animals. In healthy fish, pressures rose with exercise (from 2·72 ± 0·11 to 3·75 ± 0·19 kPa) and then rapidly returned to resting levels during recovery. In X-cell fish pressures rose during exercise, but then continued to rise, to reach a high of 4·18 ± 0·13 kPa, close to the predicted maximum pressure able to be generated by these hearts. Recovery was rapid in healthy fish, but was prolonged in diseased animals. As they are constantly swimming, there is the potential that X-cell-affected fish suffer from chronic hypertension.
Department of Zoology, University of Canterbury, Private Bag 4800, Christchurch, New Zealand and 2:
School of Life Sciences, University of Queensland, St Lucia, Brisbane, Queensland, Australia