Lungfish, the closest living relatives of tetrapods, frequently dwell in anoxic shallow swamps and ponds that dry up during the dry season, therefore these fish have evolved to be obligate air breathers and can spend lengthy periods of time out of water, holed up in tunnels in the dried mud. To breathe, the lungfish’s air bladder has developed into a “lung,” a highly vascularized region of the digestive tract that stores swallowed air to oxygenate the blood that flows through it. Their hearts are also designed to pump oxygenated and deoxygenated blood in separate streams to various regions of the body.

Protopterus is the only genus in the Protopteridae family, which includes four African lungfish species. The marbled lungfish (P. aethiopicus), the largest of these species, can grow to be 200 cm long and has the largest vertebrate genome reported to date; it also has one of the largest genomes known from any living organism (along with the freshwater amoeboid Polychaos dubium and the Japanese plant Paris japonica). They are carnivores, consuming invertebrates, fish, and amphibians. Lungfish are eaten by native Africans, although they have a strong flavor and are hence not frequently loved. Marbled lungfish numbers in Lake Victoria are declining due to increased fishing pressure and the shifting of breeding areas to cultivation.

The Gilled African lungfish (P. amphibius) is the world’s smallest lungfish, measuring approximately 44cm long. Aside from the four Protopterus species, there are two other species of lungfish: the South American lungfish (Lepidosiren paradoxa, family Lepidosirenidae) belongs to the same order (Lepidosirenifores) as the Protopteridae, and the Australian lungfish (Neoceratodus forsteri, family Ceratodontidae) is the only extant species in the Ceratodontifores order.