Lung and gill ventilation of the african lung fish

The influence of changes in ambient gas tensions on gill and lung ventilation was determined in the African lung fish. Experiments were performed with the fish in water, but with free access to the air over it. Gill and lung frequency were measured using implanted electrodes; tidal volumes were determined by spirometry and by cinéradiography. The results indicate that moderate hypoxia stimulates, whereas hyperoxia depresses, both gill and lung ventilation. Slight hypercapnia (0.5 per cent CO₂ in inspired air) increases both lung and gill ventilation whereas increasing concentrations depress both. On the other hand, the combination of moderate hypoxia and hypercapnia has different effects on gills and lungs, increasing lung frequency and depressing gill frequency. The tidal volume remained virtually unchanged despite the wide variations in lung frequency. These observations are considered with respect to the chemoreceptors which mediate the ventilatory responses.