Control of breathing in Amphipnous cuchia, an amphibious fish

Abstract

Gas exchange in the amphibious fish, Amphipnous cuchia, takes place principally by air breathing, the main site of exchange being a pair of specialized pharyngeal air sacs. Air breathing is periodic with bursts of active ventilation interrupted by periods of apnea. Active branchial ventilation of water never occurred unless fish was deprived of air. A respirometer was constructed to measure respiratory frequency ( f), tidal volume (V t), total ventilation ( V) and duration of breath cycles in response to altered ambient conditions. Hypoxie water increased V̇ 3 times mainly by an increase in f and V t. Hyperoxic water decreased V̇ was unchanged when inspired CO 2 was raised from 0 to 4%. Higher CO 2 increased V mainly by f diminished at lowered water temperature. Breathing 100% 0 2 reduced V to 1 3 of value in air. At P i o 2 75 mm Hg V increased 1.5 times while at 40 mm Hg V increased fourfold. V was unchanged when inspired CO 2 was raised from 0 to 4%. Higher CO 2 increased V̇ mainly by increasing f while V t changed little. Control of breathing in Amphipnous is discussed and compared with conditions in water-breathing and other air-breathing fishes. The periodic ventilation is primarily governed by an O 2-dependent chemosensitive mechanism. Ventilation is more sensitive to hypoxia than hypercapnia.