The lungfish is a peculiar and prehistoric freshwater fish found in South America, Africa, and Australia. Historically there were hundreds of species of this fish, although only a handful survive today, and many scientists believe that the lungfish represents a bridge from entirely aquatic to amphibious species. This fish is considered to be a threatened species, because it has lost a great deal of habitat. In Australia, conservation programs have begun to improve its status, 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 6 feet (1.8 meters) in length. The larger fish are more commonly found in Australia. The fish are mottled green in color, with fins resembling vestigial legs and long dorsal fins. They're voracious predatory fish, consuming any small fish that can be caught as well as some plant material. Some 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, they 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. They must surface to breathe oxygen, and are often found in shallow lakes and streams.
These fish 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. they can suspend themselves in this way for up to three years, seeming to grow out of the earth when the rains return.
Some aquarists keep lungfish as pets. Because they are predators, lungfish are usually kept alone or with other hardy species which can protect themselves. In addition, because they 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.