lungfish, common name for any of a group of fish belonging to the families Ceratodontidae, Lepidosirenidae, and Protopteridae, found in the rivers of Australia, South America, and Africa, respectively. Like the lobefins (coelocanths), the lungfishes are ancestrally related to the four-footed land animals. Fossil lungfish have been found in the United States, Europe, and India. Of the living specimens, the most primitive is an Australian species, a stout-bodied 5-ft (150-cm) fish with paired fins set on short stumps. The function of it single lung (all other species have two) is not clearly understood. The fins of other lungfishes have become long, wispy sense organs, and they are in general more eellike in appearance. Lungfish feed on snails and plants, storing quantities of fat for sustenance during hibernation.
Best-known are the African species, which hibernate in hard clay balls during the dry season. They line their retreat with a waterproof membrane of dried mucus and apply their mouths to tubes of this material that serve as airshafts from the cocoons to the surface of the ground. They can remain dormant in this manner for up to three years. In water, the African lungfishes breathe with gills.
The South American loalach is totally dependent on air and will drown if held underwater. Its eggs are laid in a long tunnel at the bottom of a swamp and are guarded by the male, which sprouts red filamental gills from his pelvic fins. The young are also equipped with temporary external gills.
Lungfish are classified in the phylum Chordata, subphylum Vertebrata, class Sarcopterygii, order Ceratodontiformes, family Ceratodontidae, and order Lepidosireniformes, families Lepidosirenidae and Protopteridae.