The oxygen consumption of larvae of the frog Rana berlandieri Baird was reduced during exposure to aquatic hypoxia at 25°C, and under severe hypoxia the larvae lost oxygen to the water. The larvae responded to aquatic hypoxia by increasing aerial oxygen consumption and lung ventilatory frequency, and also by altering their heart rate and gill ventilation frequency. Under severe or prolonged aquatic hypoxia without access to air, Rana larvae accumulated lactate. When prevented from breathing air, the larvae were unable to compensate fully by increasing their aquatic oxygen consumption. Body size or the interaction of body size and oxygen partial pressure significantly affected the aerial oxygen consumption, the total oxygen consumption and gill ventilation frequency, but did not affect other aspects of larval gas exchange. Anuran larvae resemble air-breathing fishes in some responses to aquatic hypoxia (e.g. increased dependence upon aerial oxygen uptake and changes in ventilatory frequencies), but are unusual in some ways (e.g. oxygen loss to the water). The interactions of body size and hypoxia are not sufficient to explain why so many anuran larvae without lungs are small.

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