Thought of as a potential precursor in the evolution of amphibians, the lungfish is an interesting and primitive animal. A freshwater fish that has evolved to survive in areas prone to long periods of drought, lungfish have developed several characteristics that allow them to thrive in environments where water is either scarce or contains very low oxygen content. One of these characteristics has given rise to their name by their ability to breathe air through a primitive but functional lung.
Another adaptation for making efficient use of low levels of oxygen is related to the structure of their heart. The majority of fish have a very simple, two chambered heart consisting of a ventricle and an atrium. In contrast, amphibian hearts are slightly more complex with three chambers consisting of a ventricle and two atria. This division gives them better separation of oxygen rich blood coming from the lungs and oxygen depleted blood coming from the rest of the body, making their oxygen usage more efficient. Unlike most fish species, lungfish have a partial separation that has formed in the heart to create a three chambered heart very similar to that of amphibians.
Of the six living species of lungfish, four are found in Africa, one species each in South America and Australia. The South American and African species are able to survive for many months in mud in a dormant state of hibernation by lowering their metabolism and using their lungs to breathe air during periods of drought. However, it is the Australian lungfish (Neoceratodus forsteri) that can be seen in the waters surrounding and flowing under the General Admission walkway. The Australian lungfish only has one lung, as compared to the two lungs found in the other species. They cannot survive long periods of time completely deprived of water, so Australian lungfish do not leave the water to hibernate in the mud during a drought. Instead, they use the ability to breathe air through their lung as a mechanism to survive in the small stagnant and poorly oxygenated pools of water that remain.
Adult Australian lungfish are very compact and have large scales that overlap. The head is wide and flat; eyes are small; body is quite thick; pectoral and pelvis fins are somewhat like broad flippers; and dorsal fin adjoins the caudal and anal fins. They are normally olive-green to dull brown on the back, may have some dark blotches scattered about and they become lighter in color on the belly.
Australian lungfish are slow-growing and long-living. The Shedd Aquarium has housed an Australian lungfish known as “Granddad” since 1933, making him more than 80 years old, as he was mature when he arrived in Chicago. They eat frogs, tadpoles, fish, shrimp, prawns, snails, earthworms, mollusks, etc., but will also eat aquatic plant material. Although these animals may not be considered as “flashy and colorful” as other new residents on the entrance walkway, they certainly add to the prehistoric group of interesting animals at the DWA.