Oxygen uptake and transport during hypoxic exposure in the sturgeon Acipenser transmontanus

Abstract

Gill ventilation, stroke volume and frequency, % O 2 utilization and oxygen uptake, and dorsal aortic blood oxygen tension, content, pH and oxygen affinity have been determined during normoxia and during a range of hypoxic exposures in the sturgeon, Acipenser transmontanus. In air-equilibrated water gill ventilation was 350 ml/kg/min. % utilization was 35–40%, and oxygen uptake at 15°C was 55–60 ml O 2/kg/h. Dorsal aortic blood P O 2 was 90 mm Hg and blood O 2 content at a normal pHa of 7.84 was 7.0 vol %. V̇g fell considerably through a reduction in branchial stroke volume when P i O 2 was reduced from 150 to 100 mm Hg. Although % utilization remained unchanged, V̇ O 2 was halved, clearly identifying Acipenser as an O 2 conformer with a critical O 2 tension just below air saturation. At a P i O 2 of 60 mm Hg V̇ O 2 was only 15% of that at normoxic levels falling to only 5% at a P i O 2 of 30 mm Hg. There was no hypoxic bradycardia. There was no repayment of an oxygen debt even after severe hypoxic exposure in Acipenser, and pHa remained unchanged under all experimental conditions, a response incompatible with lactate or succinate production. It is concluded that the sturgeon reduces total energy expenditure during hypoxic exposure, rather than switching from aerobic to anaerobic metabolism.