Department of Primary Industries & Fisheries



Noxious fish - species information

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The fish listed on this page are priority species in Queensland.  Carp, tilapia and gambusia have established populations in several Queensland waterways.  The remaining 15 species of noxious fish have not established in Queensland.


colour photo of a common carp
common carp

Carp belong to the family Cyprinidae, the largest of all fish families. Carp originated in China and spread throughout Asia. They are not native to north America or southern continents.

Three different varieties of carp are present in Australian waters.  The common or European carp (generally referred to as 'carp') the more ornamental Koi variety and the mirror carp. All are declared noxious in Queensland. The goldfish (Carassius auratus) is closely related to carp but is not listed as noxious in Queensland.Carp was originally imported into Australia as a sportfish and the goldfish is currently imported for aquarium and ornamental display purposes.

The release of these cyprinids (carp species) has resulted in their colonising many Australian freshwater systems.

The spread of carp

Colour photo of koi carp
koi carp

Carp has been present in the wild in Australia for over 100 years. The first introductions occurred in the 1850s and 1860s in Victoria and New South Wales. The carp did not spread very far from the original sites of release.

In the early-1960s a strain of carp was released at Boolarra in Gippsland, Victoria. This strain, known as the Boolarra strain, was more vigorous and resulted in a dramatic population explosion. The Boolarra strain has spread extensively throughout south-eastern Australia and has become far more widespread and problematic than any original stock.

During the 1960s an extensive and intensive program was mounted to eradicate carp from all public and private waters. This proved unsuccessful and carp spread throughout the Murray-Darling River system to Queensland.

Colour photo of mirror carp
mirror carp

Confirmed populations exist in the Condamine-Balonne catchment, Paroo River, Warrego River, Nebine Creek, Culgoa River, Barwon River and MacIntyre River. Carp in these rivers comprise approximately 20-30% of the total fish population.

Carp are also present in the Logan and Albert Rivers in south-east Queensland and in various dams. Farm dams should not be stocked with carp as their potential for spread during times of heavy rain is high. The elimination of this species is now impracticable and, although the peak invasion levels have now declined, it is presently still expanding its range. 

Impacts of carp

Carp disturb the bottom substrate through their feeding habits and may increase the turbidity (the amount of suspended silt or sediment) of the water, particularly in shallow, warm, slow-flowing waters and small bodies of still water such as farm dams. They feed by 'roiling', that is, sucking up mud and plants from the bottom, ejecting it and selecting food whilst it is suspended in the water. The actual plant material plays a relatively minor role in the diet of carp but the water appears muddy or turbid and the vegetation is physically damaged or uprooted. Modificaton of habitat due to feeding and spawning behaviour of carp may occur, but this has not been clearly documented. Carp have been implicated in the reduction of shallow-rooted and soft-leaved species of aquatic macrophytes.

Increased silt or sediment in the water decreases light penetration and photosynthesis and therefore inhibits plant growth. Aquatic plants play a vital role in freshwater environments, providing cover and protection for fish and spawning areas for some native fish species.

While there is no evidence to suggest that carp compete directly with native species, their diet includes some macro-invertebrates, which may lead to competition with many native species, although few species feed in the same way as carp. While there may be some competition for food and space, dietary overlaps appear minimal and the effects of habitat interactions have not been quanitified. Because of the large body size of carp, their longevity and rapid growth rates, carp can utilise large amounts of the total food resource. There is little evidence that carp consume native fish, and ingestion of native fish eggs is likely to be incidental.

Carp can tolerate poor environmental conditions including high turbidity, a wide range of water temperatures (4ºC to 35ºC), moderate salinities and low dissolved oxygen levels. Carp will often survive where water quality is too low to support other fish species.

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The group of fish species known as cichlids (Family Cichlidae), of which the tilapia is part, are endemic to the warm, fresh and brackish waters of Africa, South and Central America, southern India and Sri Lanka. One hundred and fifty species of cichlids have been imported into Australia for aquarium display purposes. Of these, three species have established breeding populations in Australian inland water bodies.

These are the Mozambique mouth-brooder (Oreochromis mossambicus) and the black mangrove or niger cichlid (Tilapia mariae). Other cichlids with small isolated populations in Queensland include the three-spot cichlid (Cichlasoma trimaculatum), red devil (Amphilophus citrinellus), oscar (Astronotus ocellatus ) and Victoria Burton's Haplochromine (Haplochromis burtoni).


The African cichlid Oreochromis mossambicus, known as the Mozambique mouth-brooder or tilapia, is the most widely distributed and problematic of tilapiine species. This species has established breeding populations at several sites in northern and southern Queensland.

Confirmed populations in Brisbane exist at Tingalpa Reservoir, Tingalpa Creek, North Pine Dam, North River, South Pine River, Dowes Lagoon (Sandgate), Wivenhoe Dam, Somerset Dam, Kedron Brook, Forest Lake.

Unconfirmed populations are at Lake Kurwongbah and farm dams in the North Pine Dam area.

Tilapia have been confirmed in Boondooma Dam. To prevent their spread into waterways below the dam, screens have been installed.

In Northern Queensland, tilapia populations occur in the vicinity of:

  • Townsville (T.mariae and O. mossambicus) - Ross River, Alligator Creek, Louisa Creek, Rowes Bay drainage system, Healey Creek, Bohle river, Woolcock Street drains;
  • Kewarra Beach to Palm Cove, Barron River, Port Douglas, lower Mulgrave River, lower North and South Johnstone Rivers and coastal waterways and estuaries around Cairns.
  • Unconfirmed populations in Townsville common, Yeppoon area and the Burdekin River.

The convict cichlid has a very restricted distribution. There is increasing evidence that other cichlid species are spreading into new areas.

Mozambique mouth-brooder in Queensland waters

The Mozambique mouth-brooder is readily able to establish as the dominant fish species, to the detriment of native fish populations, in freshwater and upper estuaries. Its success as an invading species can be attributed to several factors, including:

  • simple food requirements  The Mozambique mouth-brooder feeds mainly at the base of the aquatic food chain, i.e. algae, zooplankton and detritus, and therefore exploits a food resource unutilised by most native fishes. Furthermore, this species is able to switch food resources according to availability;
  • flexible habitat preferences Within Australia the Mozambique mouth-brooder has colonised a variety of aquatic habitats including large artificial reservoirs, ornamental ponds, farm dams, artificial drainage channels, freshwater and the upper sections of tidally-flushed creeks;
  • highly efficient reproductive strategy The Mozambique mouth-brooder is a prolific breeder, capable of reproducing several times a year when conditions are favourable.

The female deposits eggs in a nest constructed by the male. After the male has fertilised the eggs, the female takes them up in her mouth and incubates them for 3 to 5 days. Newly hatched fry remain in the female's mouth for another 10 to 14 days. Mouth-brooding protects the eggs and larvae until they are released as independent juveniles and effectively ensures that a high proportion of eggs survive and hatch. This allows very rapid population growth. Juveniles may also live for a considerable time in the female's mouth after the female dies. If a dead female is thrown back into a stream the young may survive and breed. The spread of tilapia may be assisted by anglers illegally using them as bait.

colour photo of a Oreochromis mossambicus juvenile
Oreochromis mossambicus juvenile

These attributes give the Mozambique mouth-brooder a competitive advantage over co-occurring fish species. Furthermore, Mozambique mouth-brooders are under little predation pressure except from the crocodile and the local larger predatory fish species (for example, barramundi), although adult Mozambique mouth-brooders are too large for native piscivorous (fish-eating) fish.

Mozambique mouth-brooders are disease-resistant and can survive in conditions too poor to support other fish species.

They have very wide environmental tolerances and can survive in temperatures between 8 and 42ºC, although temperatures greater than 16ºC are required to remain active and feed, and temperatures greater than 20 to 24ºC are required to breed.

In addition, Mozambique mouth-brooders can withstand a wide range of salinities - from 0 to about 36o/oo (parts per thousand), and low dissolved oxygen (0.1 milligrams per litre). They can survive, grow and even breed in seawater. These tolerances allow them to disperse between river systems.

colour photo of an adult tilapia , Oreochromis mossambicus, an exotic freshwater species
Oreochromis mossambicus adult

The Mozambique mouth-brooder can almost totally displace native species in rivers, lakes and estuaries as a result of its prolific breeding habits. It is likely that Mozambique mouth-brooders compete with native fishes for food and space. However, little is known about these interactions and research is required to evaluate this. Although there is little documented evidence, Mozambique mouth-brooders may also occasionally ingest the eggs and larvae of other fish.

When environmental conditions are unfavourable, for example limited food and space are available, Mozambique mouth-brooders mature and breed at considerably smaller body sizes than usual. This phenomenon is known as stunting and results in large populations of mature fish with small body sizes. Stunting is an adaptive response to environmental stress and therefore ensures the survival of the species.

Mozambique mouth-brooders are also known to breed prolifically in food-rich environments, which may lead to overcrowding, reduced growth rates and early sexual maturity. This again results in large populations of mature fish with small body sizes. These stunted populations may have the greatest impact on native fishes, as small individuals in extremely high densities may interfere with the spawning of native species.

Black mangrove cichlid in Queensland waters

 The black mangrove cichlid (T. mariae) is not a mouth brooder and prefers hard substrates to spawn. It has similar environmental tolerances to O. mossambicus but requires higher temperatures to spawn.

colour photo of a Tilapia mariae adult
Tilapia mariae adult

Black mangrove cichlid (Tilapia mariae) is found in the Cairns region, the lower Barron River and its tributaries, Leslie Creek, Freshwater Creek and also in the South Johnstone River (probably due to translocation, not natural spread). It has moved into Trinity Inlet streams and Thomatis Creek and is present in the Mulgrave and Russell rivers.


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Colour photo of a Gambusia / mosquito fish
Gambusia/ mosquito fish

Gambusia (Gambusia holbrooki), belong to a group known as livebearers (Family Poeciliidae). Livebearers or ovoviviparous fish have internal fertilisation in which embryos develop fully within the female, culminating in birth of live larvae.

These noxious fish are known to dominate fish communities in many streams in the Brisbane region, often resulting in either a reduction in native fish numbers or the total elimination of native fish species. Many of these streams have a high level of habitat disturbance.

Gambusia was first introduced into eastern Australian waters in 1929 and by 1945 this species was widespread throughout eastern Queensland. Gambusia were originally imported from North America as a mosquito control agent. They have had a minimal impact on mosquito populations and in fact they are less effective than native fish in controlling mosquitoes. They have had a detrimental effect on native fish almost everywhere they were introduced.  (See Native fish as alternatives to the exotic fish, Gambusia, for mosquito control  for information on the use of native fish as mosquito control agents.)

Gambusia are highly successful due to early maturation, a high reproductive rate, a large number of annual broods and their mode of reproduction (live bearing). This species is well known for aggressive behaviour and the habit of nipping the fins of other fish species and eating their eggs.