Control of the respiratory mode in air-breathing fishes

Abstract

The transition from water breathing to air breathing for most bimodally breathing fishes appears to be critically dependent on sensory information from three major sets of peripheral receptors. Dominant control over the respiratory mode arises from stimulation of oxygen-sensitive chemoreceptors. Stimulation of internally oriented chemoreceptors generally increases both aquatic and aerial respiration, while stimulation of external chemoreceptors may shift the ventilatory emphasis from water to air breathing. Air-breathing organ mechanoreceptors may help to reflexively stimulate or inhibit air breathing upon deflation or inflation of the air-breathing organ, and probably play a major role in matching ventilation to perfusion in the air-breathing organ. Waterborne irritants or emersion stimulate defense receptors that may override control priorities set by other receptors, and inhibit branchial ventilation in favor of air breathing. While there is still little detailed information about the distribution and characteristics of these sensory receptors, it seems likely that similar sets of receptors control the respiratory mode in most air-breathing fishes, and that differences in the central integration of this sensory information may best account for the great variability of respiratory reflex responses in this diverse group of animals.