Lungfish, a fish that breathes with a lung as well as by gills. The African and South American lungfishes use their lungs to breathe air while they estivate (are dormant) in mud in times of drought. The Australian lungfish uses its lung to breathe air when the water is stagnant.The lungfish can live out of the water for months.
When its native stream or lake dries up, an African or South American lungfish forms a cell in mud, leaving a small breathing hole, and curls its tail about its nose. Its skin secretes a liquid that looks like transparent plastic film when it dries. The film covers all but a small hole over the mouth and keeps the fish from drying out while it estivates. The lungfish can thus live out of water for months, and then resume active life when water softens the mud. African and South American lungfishes are slender-bodied and almost scaleless. They have pointed tails and stringy, tapering fins. The Australian lungfish, prized as food, grows up to six feet (1.8 m) long. It has a thick body covered with large scales, and short, stout fins.
Actually, many fish can breathe out of water. But none is better at it than a lungfish is. A lungfish breathes out of water by using a lunglike organ called a swim bladder. Some kinds of lungfish can even survive in dried-up rivers for weeks or months.
Most lungfish, like the South American lungfish, have gills that are poorly developed. They breathe air mostly with their swim bladders. If one of these lungfish couldn’t reach the water’s surface, it would drown. However, the Australian lungfish breathes mostly with its gills. It gulps air at the water’s surface only when the water doesn’t have much oxygen in it.
Lungfish are one of a few bony fish that are able to control their fins as land animals control their limbs. Most fish can only raise or lower their fin rays. But a lungfish has joints that attach the fins to its body just as arms and legs are attached to a person’s body.
Lungfishes belong to the superorder Dipnoi. There are four species of African lungfishes, all belonging to the genus Protopterus. The South American lungfish is Lepidosiren paradoxa; the Australian, Neoceratodus forsteri.