African Lungfish

1 Species Overview

The African lungfish is one of the most unusual freshwater fish alive. Beyond its gills, it can use its swim bladder as a lung to breathe air, and when waters recede it burrows into the mud and enters aestivation — a summer dormancy — to wait out the dry season.

It is a lobe-finned bony fish (class Osteichthyes, subclass Sarcopterygii). Living lungfish make up the orders Ceratodontiformes and Lepidosireniformes, families Neoceratodontidae and Lepidosirenidae, distributed across the equatorial regions of Africa, Australia, and South America.

2 Morphological Characteristics

What sets the African lungfish apart is its ability to breathe with its swim bladder in place of lungs. Although it is not a true lung-breather, this lets it survive the dry season: even when a river dries up, it slips into the mud and aestivates for months at a time (within limits).

In fresh water it breathes mainly with gills but supplements with the bladder-lung. Its bladder is highly developed — the front part is a short single chamber that then splits into paired chambers reaching the rear of the body cavity; the chamber walls form many small air sacs (alveoli) much like the lungs of land animals.

Because the bladder is built like a lung, rich with branching blood vessels and a spiral valve, a short duct links it to the esophagus so the fish can take in oxygen and expel carbon dioxide when the water is poorly oxygenated. Remarkably, in the dry season it digs a sturdy ‘mud burrow,’ opens a tiny breathing hole at the mouth, and lies dormant through up to six months of drought, breaking out when the rains return.

3 Habitat & Living Environment

Often called a living fossil, the African lungfish is increasingly at risk: as people learn more about it, scientists have found the waters it breeds and lives in are shrinking, putting wild populations under threat.

Modern African lungfish live mainly in rivers and can reach 1–2 m in length; their skulls are weakly ossified, the spine is cartilaginous, and the scales are reduced to small bony cycloid scales. Four species occur, mostly in rivers and large lakes near equatorial Africa, ranging north to Senegal and south to Mozambique. Like their South American relatives, they have paired lungs and relatively small gill covers; when a river dries out completely they tunnel into the riverbed mud and aestivate up to six months, leaving the water entirely to survive on air. Columnar mud deposits with scattered lungfish fossils from the Carboniferous and Permian show they have weathered hard times this way for hundreds of millions of years.

4 Feeding Guidelines

African lungfish are carnivorous, feeding mainly on fish, mollusks, crustaceans, insect larvae, and worms. Also known as the proto-fin fish or tiger-spotted lungfish, they need sensible, scientific feeding in captivity.

Individuals vary greatly in size and color; some are striped, some are not, yet no two patterns are alike — the markings work like a fingerprint to tell them apart. Young fish have external gills that persist as they grow but gradually shrink and atrophy; they grow quickly.

Their eyesight is poor, but their sense of smell is keen, and they emit a faint electric field to sense nearby life, so they react sharply at feeding time.

Although they prefer live prey such as small fish and shrimp and are not aggressive by temperament, be careful during feeding and water changes: their sharp teeth and powerful jaw bite can inflict surprisingly severe injury.