The partitioning of oxygen uptake from air and from water by erythrinids

Oxygen uptake from air and from water was measured during routine activity at 29 °C in two facultative air-breathing teleosts, Hoplerythrinus unitaeniatus and Erythrinus erythrinus. These fish breathe air in hypoxic water, taking a breath every 1 to 2 min. Gill ventilation increases in hypoxic water if air breathing is prevented, but decreases if air breathing is permitted. Average oxygen uptake from water is 105 mg∙h−1∙kg−1 and 69 mg∙h−1 kg−1 from air for Hyplerythrinus; 65 mg∙h−1∙kg−1 from water and 51 mg∙h−1∙kg−1 from air for Erythrinus. In normoxic water Hoplerythrinus obtain from 0 to 56% of oxygen uptake (mean 31%) from air. Two Hoplerythrinus survived in air for 24 h and did not have an elevated oxygen uptake when put back into water.