Air breathing and aquatic gas exchange during hypoxia in armoured catfish

Air breathing in fish is commonly believed to have arisen as an adaptation to aquatic hypoxia. The effectiveness of air breathing for tissue O2 supply depends on the ability to avoid O2 loss as oxygenated blood from the air-breathing organ passes through the gills. Here, we evaluated whether the armoured catfish (Hypostomus aff. pyreneusi)—a facultative air breather—can avoid branchial O2 loss while air breathing in aquatic hypoxia, and we …