A distinctive characteristic of the Australian lungfish is the presence of a single dorsal lung, used to supplement the oxygen supply through the gills. During times of excessive activity, drought, or high temperatures (when water becomes deoxygenated), or when prevailing conditions inhibit normal functioning of the gills, the lungfish can rise to the surface and swallow air into its lung. More frequent air breathing is correlated with periods of greater activity at night when it uses the lung as a supplementary organ of respiration.
