A comparative study of the oxygen equilibria of blood from 40 genera of Amazonian fishes

Abstract 1. We have examined the oxygen-affinity of the fresh, whole blood from representatives of 40 genera of Amazonian fishes. 2. When all the air-breathing fishes and all the water-breathing fishes were considered, no differentiation in oxygen affinity could be distinguished, although in two cases of closely related species, i.e. Osteoglossum , a water breather, vs Arapaima , an air breather, and Hoplias , a water breather, vs Hoplerythrinus , an air breather; the air breathers have bloods with lower oxygen affinity than do the water breathers. 3. Significant differences in the oxygen affinity were found when fishes were considered by habitat: the oxygen affinities were in general correlated with available environmental oxygen and relative oxygen demand of the fishes.