CARDIOVASCULAR RESPONSES OF THE RED-BLOODED ANTARCTIC FISHES PAGOTHENIA BERNACCHII AND

The aim of this study was to investigate cardiac performance and cardiovascular control in two red-blooded nototheniid species of antarctic fishes, Pagothenia bernacchii (a benthic fish) and P. borchgrevinki (a cryopelagic fish), and to make comparisons with existing information on haemoglobin-free antarctic teleosts. In quiescent P. bernacchii at 0°C ventral aortic pressure (PVA) was 3.09kPa and cardiac output (Q) was 17.6mlmin~1kg~1, with a heart rate (fn) of 10.5 beats min"1 and stroke volume of 1.56 ml kg"1. Following atropine treat-ment, Q was maintained but heart rate increased and stroke volume decreased. Resting heart rate resulted from an inhibitory cholinergic tone of 80.4 % and an excitatory adrenergic tone of 27.5%. The intrinsic heart rate was 21.7 beats min"1 at 0°C. In quiescent P. borchgrevinki at 0°C, PVA was 3.6 kPa, Q was 29.6mlmin~1 kg"1 and stroke volume was 2.16 ml kg"1. The resting heart rate in P. borchgrevinki of 11.3 beats min"1 resulted from an inhibitory cholinergic tone of 54.5 % and an excitatory adrenergic tone of 3.2 %. The intrinsic heart rate wa