Introduced Animals
Carp (Cyprinus carpio)
Carp originated in Asia and today is widely distributed throughout Europe, Canada, United States and Africa.
| Australia has four strains of carp. It was imported into Australia 150 years ago for the stocking of fish dams. Carp are now distributed throughout the whole Murray-Darling Basin and as a result are an ecological problem. Carp are very mobile and find it easy to spread throughout Australia’s river systems, as they travel in floodwaters and their eggs can be transported by birds to different areas. Carp are characterised by barbels or whiskers on their upper lip. They also have a deeply forked tail, a single dorsal fin and large scales. |
| Carp have affected the river environment in a number of ways. When feeding, carp are likened to a vacuum cleaner in the way they suck up everything and blow out what they do not need. Water quality is reduced when carp are feeding as they stir up sediments and increase the turbidity of the water. Carp increase erosion of stream banks, channels and levees by undermining them. In the feeding process carp uproot vegetation and as a result destroy the breeding habitat of native fish. Native fish have to compete with carp for food. Carp however do not eat native fish.
Carp numbers are now estimated to be between 70 per cent and over 90 percent of fish biomass in the rivers of the Murray-Darling Basin. Carp have been declared a pest fish in most Australian states.
It is ILLEGAL to return carp to the water once you have caught them.Mosquitofish (Gambuisa affinis)
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| Mosquito fish are native to North America and were introduced to control mosquito larvae (but does not prefer mosquito wrigglers to other invertebrates). Mosquito fish feed on a wide variety of foods. They eat insects such as ants and flies together with aquatic beetles, bugs and other fauna. Mosquito fish, with their high reproductive rate and extended breeding season, may overwhelm suitable habitats with juveniles and deplete food supplies. They are now present in nearly every wetland. |
Redfin perch (Perca fluviatilis) The earliest recorded introduction into Australia was in 1862. It was introduced as a sporting fish and for recreational angling.
Redfin prefers slow moving water that has aquatic vegetation growth, and is able to feed on a wide range of foods including crustaceans and molluscs. They are heavy predators of fish species and can breed rapidly.
Redfin perch are considered to be a major threat to our native fish species. Release following capture is illegal. |
| Tench (Tinca tinca)
| The Tench is capable of growing up to about 50cm long. It was introduced into the River Murray by acclimatisation societies in 1876 and spread rapidly throughout the Murray Darling System. Its numbers reduced drastically in the 1970's when Carp (Cyprinus carpio) became abundant. Other introduced fish pose a more serious problem to native fishes than Tench. |
Goldfish (Carassius auratus) | Extremely widespread species found throughout the Murray Darling Basin The Goldfish was imported into Australia in the 1860's as an ornamental fish. It has the capacity to survive in extremely degraded habitats and therefore does well in slow waters of high temperature and low oxygen content. It also has the capacity to feed on a variety of foods including plant materials, organic detritus, small aquatic insects and other animals. |
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Cats
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Cats that have become wild or feral threaten small native animals and birds. Bigger and more aggressive than domestic cats, these feral cats are difficult to control.
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Foxes Foxes were introduced for hunting and have spread since because there are few native predators in Australia to rival them. Along the River Murray, they prey on animals that live on the ground, especially rabbits and tortoises that breed on the riverbanks. When rabbit numbers crash because their plant food is low, foxes prey on native animals and birds.
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Rabbits | 
| Rabbits are very adaptable and breed quickly, which is why they flourish. They compete with livestock for food and water. They degrade pasture and damage crops. Grazing down to ground level, they eat the shoots, roots and the seeds of plants. These plants can’t reshoot and so they die. This leaves the soil vulnerable to erosion. Bare ground in turn encourages weeds to invade. The resulting decrease in the diversity of plants affects the native animals that depend on different species for food and shelter. |
Goats and Pigs | Goat and Pigs are also pests along the river, but less so than rabbits and foxes. Goats climb into low-branching trees and eat all the leaves as well as the bark, which often kills the trees, especially young ones. Pigs destroy the root of plants as they search for food. Both animals have hard hooves that compact the soil and wear down plant cover more quickly than the soft-padded native animals. | 
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Photos provided by the Murray-Darling Basin Commission
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