Fish

More than 4,400 species of fish inhabit Australia's waterways; of these, 90% are endemic. Australia has a relatively small freshwater fish fauna of only 170 species—this may be related to the relative scarcity of freshwater waterways in the continent. Two families of freshwater fish have ancient origins: the Queensland Lungfish and the bony tongues. The Queensland Lungfish is most primitive of the lungfish, having evolved before Australia separated from Gondwana. The Salamanderfish, peculiar to the southwest of Western Australia, is one of the smallest freshwater fish and can survive dessication in the dry season by burrowing into mud. Other families with a potentially Gondwanan origin include the Retropinnidae, Galaxiidae, Aplochitonidae and Percichthyidae. Apart from the ancient freshwater species, 70% of Australia's freshwater fish have affinities with tropical Indo-Pacific marine species that have adapted to freshwater. These include freshwater lampreys, herrings, catfish, rainbowfish, and some 50 species of gudgeon, including the Sleepy Cod. Native freshwater game fish include the Barramundi, Murray Cod, and Golden Perch. Two species of freshwater shark are found in the Northern Territory, both endangered.

A number of exotic freshwater fish species, including Brown, Brook and Rainbow Trout, Atlantic and Chinook Salmon, Redfin Perch, Carp and Mosquitofish have been introduced to Australian waterways, with serious detrimental effects.

The Mosquitofish are a particularly aggressive species known for nipping the fins of other fish and have been linked to the decline of, and localised extinctions of several small native fish species.

The predatory introduced trout species have had serious negative impacts on a number of upland native fish species including Trout Cod, Macquarie Perch, and Galaxias species as well as other upland fauna such as the Spotted Tree Frog. The Common Carp has been conclusively linked with the loss of aquatic vegetation.

Most of Australia's fish species are marine. Groups of interest include the Moray eels, squirrelfish, pipefish and seahorses, whose males incubate the eggs in a specialised pouch. There are 80 species of grouper in Australian waters, including one of the world's biggest bony fish— the Giant Grouper— which can grow as large as 2.7 m and weigh up to 400 kg. The trevally, a group of 50 species of silver schooling fish, and the snappers are popular species for commercial fishing. The Great Barrier Reef

Sharks inhabit all the coastal waters and estuarine habitats of Australia’s coast. There are 166 species, including 30 species of requiem shark, 32 of catshark, six of wobbegong shark, and 40 of dogfish shark. There are three species from the family Heterodontidae: the Port Jackson Shark, the Zebra Horn Shark and the Crested Horn Shark. In 2004, there were 12 unprovoked shark attacks in Australia, of which two were fatal. Only 3 species of shark pose a significant threat to humans; the Bull shark, the Tiger Shark and the Great White Shark. Some popular beaches in Queensland and New South Wales are protected by shark netting, a method that has reduced the population of both dangerous and harmless shark species through accidental entanglement. The overfishing of sharks has also significantly reduced shark numbers in Australian waters, and several species are now endangered. A Megamouth Shark was found on a Perth beach in 1988; very little is known about this species, and this discovery may indicate the presence of the species in Australian coastal waters.