Due to its geographical situation and isolation Australia has distinct fish fauna, including many endemic species. From the 18th century, early colonisers began introducing a number of exotic species including mammals, plant, birds and fish. The introduction of such fish has led to serious ecological damage, most notable being the effect of common carp in the Murray-Darling Basin. Introduced carp now dominate the freshwater systems of southern Australia. While the damaging impact of carp is well recognised, little in the way of control measures have been employed to control their spread. Their ability to colonise almost any body of water, even those previously considered to be beyond their physical tolerances, is now well established. Control of exotic fish species is being undertaken by various government departments, though many problems are faced.
Introduced trout species dominate the upland reaches of rivers in southeast Australia, and may have negative effects on upland native fish like the mountain galaxias species, Macquarie perch and the unfortunately named trout cod, but due to their popularity as sport fish, lack of historical records, and loss of angling memories, their damaging effects are not widely understood.
All recently established exotic fish in Australia stem from the illegal release of aquarium fish species. With the continued and largely uncontrolled importation of many high-risk fish species for the aquarium industry, Australia continues to be at risk of further invasions of exotic fish.
