Breathing
A distinctive characteristic of the Queensland lungfish is the presence of a single dorsal lung, used to supplement the oxygen supply through the gills. During times of excessive activity, times of 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. It has been shown that more frequent air breathing is correlated with periods of greater activity at night when it uses the lung as a supplementary organ of respiration.
Unlike the South-American and African lungfishes, the Australian species has gills on all the first four gill arches, while the fifth arch bears a hemibranch. It is also the only lungfish species that is a facultative air breather, only breathing air when there is not enough oxygen in the water to meet their needs. The lung is a single long sac situated above and extending the length of the body cavity, and is formed by a ventral outgrowth of the gut. Internally, the lung is divided into two distinct lobes that interconnect along its length, compartmentalized by the infolding of the walls. Each compartment is further divided to form a spongy alveolar region. Blood capillaries run through this region close enough to the air space in the lung to enable gas exchange. Lungfish breathe in using a buccal force-pump similar to that of amphibians. The contraction of smooth muscles in the walls of the lung results in exhalation.
The sound of the lungfish exhaling air at the surface prior to inhaling a fresh breath has been compared to that made by a small bellows. Young lungfish come to the surface to breathe air when they are about 25 mm long.
Read more about this topic: Queensland Lungfish
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