Abstract
The mechanisms of aquatic and aerial ventilation in four bimodally breathing species of teleosts of the genus Channa were studied by high-speed light and X-ray ciné films, pressure transducer recordings and electromyography. Neither inter- nor intraspecific differences were found in the pattern of aquatic and aerial ventilation. Aquatic ventilation proceeds with a partially air-filled buccopharyngeal cavity. The electromyographic patterns, pressure waveforms in the buccal and opercular cavities, and kinematics of jaw and opercula resemble those found for aquatically breathing teleosts. The pattern of aerial ventilation differs significantly from that of aquatic ventilation. Aerial ventilation is initiated by a reversed flow of water brought about by a low pressure in the buccal cavity. In this way the air in the suprabranchial cavity is moved forward and expelled from the mouth. The buccal, suprabranchial and opercular pressures are maintained at below ambient pressures throughout the aerial respiratory cycle. The kinematic pattern of bone movements, pressure waveforms and electromyographic profiles during air ventilation are identical to those of the cough and do not differ interspecifically. The complex aerial ventilation mechanism in Channa may be homologous with the primitive cough mechanism. Fishes employing the cough mechanism for air ventilation remain totally dependent on water and are therefore poorly adapted to explore terrestrial habitats.
