Lungfish is a type of fish that can breathe out of water. It breathes air by means of a lunglike organ called a swim bladder or gas bladder. The lungfish is one of the oldest known kinds of fish. Scientists have found fossils of lungfish that date from about 400 million years ago. Scientists believe that land-dwelling vertebrates (animals with a backbone) developed from fish similar to the lungfish.
There are several species (kinds) of lungfish. They live in freshwater marshes, swamps, and rivers. They are found in Africa, Australia, and South America. African lungfish are the largest kind. Some grow up to 7 feet (2 meters) long.
The Australian lungfish breathes chiefly with its gills. It gulps air at the water’s surface only when the water contains little oxygen. This lungfish has a long, broad body and two pairs of flipperlike fins.
African and South American lungfish are eel-shaped with two pairs of long, threadlike fins. These lungfish have poorly developed gills and breathe almost entirely with their “lung.” If held underwater, they will drown. African and South American lungfish can survive hot, dry periods when the water in which they live dries up. At such times, they tunnel into the mud and remain there inactive until the rains return. This behavior is called estivation. During estivation, lungfish live off protein stored in their muscle tissues. African lungfish estivate inside a cocoon made of mud and a slimy substance given off by their bodies. This cocoon can be easily dug from the ground and the fish removed for food.
Lungfish eat mainly small fish and other water animals, such as frogs and snails. Female lungfish lay eggs. Among African and South American lungfish, the males fiercely protect the eggs and young.
