Gas exchange in fish with and without hemoglobin

Abstract

Hemoglobinless antarctic icefish exposed to P i O 2 , levels of 600 –700 mm Hg reduced their gill irrigation and cardiac output. Cardiac output was reduced by a decrease in heart rate while stroke volume remained relatively constant. Ventral and dorsal aortic blood pressure decreased slightly. The response to hypoxia was an increase in gill irrigation accomplished by a large increase in respiratory amplitude. There was an atropine abolishable bradycardia and ventral and dorsal aortic blood pressure increased slightly. The icefish could not withstand P i O 2 levels below 40 –50 mm Hg for long whereas red blooded antarctic fish tested could withstand a P i O 2 of 14 – 18 mm Hg. A simple analysis of the icefish oxygen transport system showed that a tiny amount of hemoglobin might greatly extend the resistance to hypoxia. It is suggested that in cold environments fish which appear to be independent of their hemoglobin for normoxic conditions may primarily use their hemoglobin under hypoxic conditions. Such a role for hemoglobin would emphasize the dissociation characteristics rather than the quantity of hemoglobin.