The lungfish is a peculiar and prehistoric freshwater fish found in South America, Africa, and Australia. Historically there were hundreds of lungfish species, although only a handful survive today, and many scientists believe that the lungfish represents a bridge from entirely aquatic to amphibious species. The lungfish is considered to be a threatened species, because it has lost a great deal of habitat. In Australia, conservation programs have begun to improve the status of the lungfish, but it is not faring so well in other parts of the world.

The lungfish resembles an over-sized eel, with some specimens weighing up to 25 pounds (11 kilograms) at maturity and reaching six feet (1.8 meters) in length. The larger fish are more commonly found in Australia. Lungfish are mottled green in color, with fins resembling vestigial legs and long dorsal fins. The lungfish is a voracious predatory fish, consuming any small fish that can be caught as well as some plant material. Some lungfish have been known to live to over 80 years in age, with several such senior citizens being kept in captivity.

Lungfish gain their peculiar name from the lung, or bladder, that they possess. In addition to filtering the oxygen out of water, lungfish are also capable of breathing air and some species will in fact drown if held underwater. This adaptation allows the fish to survive in environments with low oxygen levels and means that they can often be found in areas with very minimal water. Lungfish must surface to breathe oxygen, and are often found in shallow lakes and streams.

Lungfish enjoy muddy stream beds, and will burrow into them to lay eggs and nest. In addition, some species have been known to go into dormancy during dry spells by digging deep into muddy areas and building a cocoon with an air hole to supply the fish until water levels rise again. Lungfish can suspend themselves in this way for up to three years, seeming to grow out of the earth when the rains return.

Lungfish are kept by some aquarists who can accommodate larger fish species. Because the lungfish is a predator, lungfish are usually kept alone or with other hardy species which can protect themselves. In addition, because lungfish like to burrow, a high volume filtration system is needed to keep the water clear. They certainly make a unique addition to fish collections, with their surprisingly expressive faces and archaic look.