What are the characteristics of lungfish? Information about the classification, facts, description of lungfish.
LUNGFISH, any of a group of archaic air-breathing freshwater fishes, making up the order Dipnoi. Unlike most other fishes, lungfishes have internal organs that are related in function and embryologic origin to the lungs of land vertebrates. Lungfish were first known from fossil remains, the earliest of which date from the early Devonian period, more than 400 million years ago. There are six living species of lungfish—one in Australia, one in South America, and four in Africa.
The Australian lungfish, or barramundi (Neoceratodus forsteri), the only living membfer of the family Ceratodontidae, is a rare and legally protected fish found only in two small rivers in the southeastern part of Queensland. Anatomically it is the most primitive of the living lungfishes. It may reach 6 or 7 feet (about 2 meters). The elongated trunklike body is covered with large scales and has a tapering tail fin connected to dorsal and anal fins. Its paired pectoral and pelvic fins, used for support and locomotion, are muscular, scaly paddles with marginal fringes of rays. The barramundi can live out of water for 8 to 10 hours if wrapped in damp cloth or vegetation. But it depends on gills as well as on lungs for obtaining oxygen and under normal circumstances is not found out of water. It is, however, able to live in highly stagnant water, where it rises to the surface at frequent intervals to fill its single lung with fresh air. The barramundi is generally nocturnal and feeds on water plants and small animals that it grinds with its platelike teeth.
The South American lungfish (Lepidosiren paradoxa) and the four African lungfishes (genus Protopterus) are classified together in the family Protopteridae. They are all elongate, eel-like fishes with relatively small scales and slender whiplike pectoral and pelvic fins. Most are 2 1/2 to 3 feet (75-90 cm) long but larger examples are not rare. The young resemble some salamanders in having feathery external gills and a ventral sucker with which it adheres to vegetation. Protopterids have fewer gills than the barramundi and depend to a greater extent on their paired lungs, through which they obtain about 95% of their oxygen. Protopterids will drown if prevented from coming to the surface to breathe. They can live out of water for a long time. During the dry season, they burrow in the muddy bottom of a swamp and form a thick mucous cocoon that becomes encapsulated in a dry shell of mud. They can aestivate in this state, with their metabolism at a very low rate, for as long as 18 months, but in nature they need only wait until the next rainy season floods the swamps.