Gas exchange in an air-breathing fish, the snakehead Channa argus, in normoxic and hypoxic water and in air.

Abstract

Gas exchange in an air-breathing fish, the snakehead Channa argus, was measured when the fish breathed bimodally in normoxic (PW, O2≥130mmHg) and hypoxic (PW, O2≤40 mmHg) water and when the fish was exposed to air at 25°C. During bimodal breathing, total ?? O2 and total ?? CO2 remained constant regardless of change in PW, O2. Of the total ?? CO2 about 60% and 85% were satisfied by air breathing in normoxic and hypoxic water, respectively. Contribution of air breathing to total ?? CO2 was small (about 15% of the total) and was unaffected by PWO2. Thus, water breathing contributed mainly to CO2 release and less to O2 uptake. When the fish was exposed to air, ?? O2 and ?? CO2 did not significantly differ from total ?? O2 and ?? CO2 during bimodal breathing. The gas exchange ratio was 0.75 in this condition. Frequency of gill ventilation markedly increased after the fish was returned to water, and this may imply that CO2 accumulated to some extent during exposure to air.