The lungfish, which is more than 400 million years old, is the oldest "ancestor" of fish, and is the collective name for all air-breathing fish, both extant and extinct in some species. Lungfish are thought to have been the first animals to try to switch from aquatic to terrestrial life, and are a "living fossil" in the history of biological evolution, now found in rivers and lakes in South America, Africa and Australia.

The Australian barramundi is the most primitive of the three regional barramundi, and is native to Queensland, Australia. The body is long and pike-shaped, about 125 centimeters in length, covered with large, thin, round scales, with paddle-shaped pectoral and ventral fins, and the dorsal, caudal, and anal fins connected as one. The Australian lungfish can breathe with both gills and lungs, or with either lungs or gills alone, and comes to the surface to breathe air during the dry season when river flow is reduced, using its individual lungs, which are distributed with many blood vessels, for respiration. However, this fish cannot yet live out of the water.

The South American lungfish and the African lungfish belong to the American lungfish family. The body is elongated and eel-shaped, with tiny round scales arranged in compound tiles on the back, and the body of the African lungfish is mottled with yellow. Both species also have no distinction between the caudal and anal fins, the even fins are radial or whip-like, and the ventral fins are far posterior. The even fins of the African lungfish degenerate into a long, thin whip-like shape, while the even fins of the South American lungfish are also significantly reduced in size, becoming rather small appendages.

Unlike the Australian lungfish, the African and South American lungfish have two lungs and are able to survive for many months after the rivers they inhabit have completely dried up. When the dry season arrives, these lungfish burrow into the mud and encase themselves, leaving only one or a few small holes to ventilate to the outside world so that they can breathe, and can survive for more than 20 days in water that is completely devoid of oxygen.

The lungfish have a very peculiar physiological phenomenon, in the hot summer they will burrow into the deep mud, the body will be balled up, stop eating and the consumption of the body's various organs to a minimum, into a kind of dormant state. When the rainy season comes and the riverbed refloods, the lungfish awakens.