The Queensland lungfish, Neoceratodus forsteri (also known as the Australian lungfish, Burnett salmon, and barramunda), is the sole surviving member of the family Ceratodontidae and order Ceratodontiformes. It is one of only six extant lungfish species in the world. Endemic to Australia, the Ceratodontidae are an ancient family belonging to the subclass Sarcopterygii, or fleshy-finned fishes.
Fossil records of this group date back 380 million years, around the time when the higher vertebrate classes were beginning to evolve. Fossils of lungfish almost identical to this species have been uncovered in northern New South Wales, indicating that Neoceratodus has remained virtually unchanged for well over 100 million years, making it a living fossil and one of the oldest living vertebrate genera on the planet.
It is one of six extant representatives of the ancient air-breathing Dipnoi (lungfishes) that flourished during the Devonian period (about 413-365 million years ago) and is the most primitive surviving member of this lineage. The five other freshwater lungfish species, four in Africa and one in South America, are very different morphologically from N. forsteri. The Queensland lungfish can live for several days out of the water, if it is kept moist, but will not survive total water depletion, unlike its African counterparts.
The small settlement of Ceratodus, Queensland, derives its name from that of the Queensland lungfish.
The Queensland lungfish is native only to the Mary and Burnett River systems in south-eastern Queensland. It has been successfully distributed to other, more southerly rivers, including the Brisbane, Albert, Stanley, and Coomera Rivers, and the Enoggera Reservoir in the past century. The Queensland lungfish has also been introduced to the Pine, Caboolture, and Condamine Rivers, but current survival and breeding success are unknown. Formerly widespread, at one time at least seven species of lungfish were in Australia.
This species lives in slow-flowing rivers and still water (including reservoirs) that have some aquatic vegetation present on banks. It occurs over mud, sand, or gravel bottoms. Australian lungfish are commonly found in deep pools of depths between 3 and 10m and live in small groups under submerged logs, in dense banks of aquatic macrophytes, or in underwater caves formed by the removal of substrate under tree roots on river banks. The lungfish is tolerant of cold, but prefers waters with temperatures between 15 and 25ºC.
The Queensland lungfish is incapable of surviving complete desiccation of its habitat, although it can live out of water for several days if the surface of its skin is constantly moist. Unlike the African species, Protopterus, it does not survive dry seasons by secreting a mucous cocoon and burying itself in the mud.
The Queensland lungfish is essentially a sedentary species, spending its life within a restricted area. Its home range rarely extends beyond a single pool or, occasionally, two adjacent pools. It does not follow a set migratory path, but may actively seek out suitable spawning habitats between July and December.
Queensland lungfish are olive-green to dull brown on the back, sides, tail, and fins, and pale yellow to orange on the underside. They have been described as having a reddish colouring on their sides which gets much brighter in the males during the breeding season. This colouration is the only distinguishing sexual characteristic of the lungfish. They have stout, elongated bodies and flattened heads with small eyes. The mouth is small and in a subterminal position. The lungfish can grow to a length of about 150 cm (4.9 ft), and a weight of 43 kg (95 lb). It is commonly found to be about 100 cm (3.3 ft) and 20 kg (44 lb) on average. Both sexes follow similar growth patterns, although the females grow to a slightly larger size. They are covered in slime when taken from the water.
The skeleton of the lungfish is partly bone, and partly cartilage. The vertebrae are pure cartilage, while the ribs are hollow tubes filled with a cartilaginous substance. The body of the lungfish is covered with large, bony scales. Ten rows occur on each side, grading to small scales on the fins. The scales are each embedded in their own pockets, and overlap extensively, such that vulnerable areas of the body are covered by a thickness of at least four scales. Two unusually large and thick interlocking scales cover the back of the head where the bony skull is thin. They have powerful diphycercal tails that are long and paddle-shaped. The pectoral fins are large, fleshy, and flipper-like. The pelvic fins are also fleshy and flipper-like and situated well back on the body. The dorsal fin commences in the middle of the back and is confluent with the caudal and anal fins.
The dentition of the lungfish is unusual: two incisors, restricted to the upper jaw, are flat, slightly bent, and denticulated on the hind margin. These are followed by dental plates on the upper and lower jaws.
Juveniles have different body proportions from mature adults. The head is rounder, the fins are smaller, and the trunk is more slender. The mouth is initially terminal, but shifts back as the fish grows. The dorsal fin typically reaches to the back of the head in young juveniles, and gradually moves caudally until it only extends to the mid-dorsal region in adults. They show a gradual change in body form as they develop, but no metamorphosis is externally detectable and no obvious point occurs at which they can be termed adult. As a juvenile, the lungfish is distinctly mottled with a base colour of gold or olive-brown. Patches of intense dark pigment will persist long after the mottling has disappeared. Young lungfish are capable of rapid colour change in response to light, but this ability is gradually lost as the pigment becomes denser.
The lungfish is reputed to be sluggish and inactive, but it is capable of rapid escape movements with the use of its strong tail. It is usually quiet and unresponsive by day, becoming more active in the late afternoon and evening.