Carp (Cyprinus carpio)
Other common names: Oriental carp, European carp, common carp, koi
Common carp Photo: Gunther Schmida
Koi variety Photo: Gunther Schmida
Introduction
Carp are a large freshwater fish native to central Asia. Introductions in many countries have helped to make carp the most widely distributed freshwater fish in the world. They are extensively farmed in Europe, Asia and the Middle East, and are a popular angling fish in Europe. However, in North America, Canada and Australia, carp are considered a significant pest.
Carp are very versatile, and can live in a great variety of habitats including highly degraded areas. Over the past few decades carp have spread across most of south-eastern Australia. They are now the most abundant large freshwater fish in some areas, including most of the Murray-Darling basin, and are thought to have contributed to the degradation of our natural aquatic ecosystems.
Description & biology
Description: Carp, along with goldfish (Carassius auratus), roach (Rutilus rutilus) and tench (Tinca tinca), belong to the Cyprinidae family.
Although small carp can be mistaken for goldfish, carp can be distinguished by having a pair of barbels (whiskers) at each corner of their mouth. They have small eyes, thick lips, a forked tail and a single dorsal (top) fin with strongly serrated spines. The scales are large and thick. Some variants, known as mirrored carp, are only partly scaled, with a few very large scales in patches or along the midline.
The colour of carp varies. In the wild, they are usually olive green to bronze or silvery in colour with a paler underside. Koi carp are an ornamental strain which are brightly coloured with orange, yellow, white and black markings. If they escape into the wild, however, koi carp soon revert to the wild colouring. All strains belong to the same species, Cyprinus carpio.
Carp can grow to a very large size, with reports of fish as large as 1.2 metres in length weighing 60 kg. Fish of up to 10 kg have been caught in Australia, but weights of around 4-5 kg are more common.
Habitat: Carp are usually found in still or slowly flowing waters at low altitudes, especially in areas where there is abundant aquatic vegetation. They are also found in brackish lower reaches of some rivers and coastal lakes.
They are capable of tolerating a range of environmental conditions. They have a greater tolerance of low oxygen levels, pollutants and turbidity than most native fish, and are often associated with degraded habitats, including stagnant waters.
Changes to water flows, declining water quality and other changes to river habitats over the past few decades have negatively affected many native fish while favouring carp.
Feeding: Carp are omnivorous, and their diet varies depending on what is available. They consume a range of small food items such as molluscs, crustaceans, insect larvae and seeds. These food items are sucked up (along with mud and water) from the bottom and filtered out using the gill rakers.
They can also consume plant material and general organic matter, especially when other food sources are not available (during winter, for example).
Carp rarely eat fish, but may consume fish eggs and larvae and disturb breeding sites.
Where are they in NSW?
The distribution of carp in NSW now includes most of the Murray-Darling Basin as well as some coastal river systems (including the Hawkesbury-Nepean, Shoalhaven and Richmond rivers and Prospect Reservoir). Carp are now the most abundant fish species in many NSW rivers, accounting for 90% of the fish biomass (total weight of fish caught) in some areas of the Murray-Darling Basin.
NSW Department of Primary Industries and its employees disclaim any liability for an act done on the basis of information in the map and any consequences of such acts or omissions.
NSW Department of Primary Industries and its employees disclaim any liability for an act done on the basis of information in the map and any consequences of such acts or omissions.
How did they get here?
Carp have been introduced into Australia both deliberately, in an attempt to imitate the European environment, and accidentally, through the escape of ornamental or aquaculture fish.
In Victoria, stocking began as early as 1859, but early stocking attempts were not successful. An ornamental strain was released near Sydney around 1850-60, and a Singaporean koi strain was accidentally released in the Murrumbidgee area in 1876.
A third hybrid strain was imported for aquaculture in Victoria in 1961 and was bred in a dam at Boolara, near Mildura. Although this venture was banned, some fish escaped and soon spread up the Murray and Darling Rivers, assisted by floods (especially in the mid 1970s). They interbred with the koi strain in the Murrumbidgee to produce a genetically diverse population of wild carp.
Carp have since gone on to radiate very successfully throughout the large inland Murray-Darling system, including in Queensland and South Australia as well as NSW and Victoria. Carp now also occur in some coastal catchments, and have recently been found in Lake Crescent and other waterways near Sorell, in Tasmania.
Their spread has been assisted by anglers who use them for live bait or deliberately stock them to create carp fisheries. A number of new populations have become established through accidental or deliberate releases of the koi strain.
What are their impacts?
Because of their adaptability, carp have been very successful in their colonisation of new environments.
Carp are widely believed to have detrimental effects on native aquatic plants, animals and general river health, particularly through their destructive feeding habits.
Carp are often found in degraded areas, although it is not clear whether they cause the degradation or are simply able to survive in areas where native fish have been eliminated. While in some cases carp have probably been blamed for degradation that is actually the result of human activities, it is clear that they can have major impacts.
Some of the probable impacts of carp are outlined below.
Reduced water quality: Carp contribute to poor water quality by uprooting vegetation and stirring up sediments during feeding, leading to increased turbidity.
This in turn reduces light penetration, which can make it difficult for native fish that rely on sight to feed. Reduced light can also decrease plant growth, and suspended sediments can smother plants and clog fishes' gills.
The effects of carp on water quality are well documented; however, poor catchment management practices probably have a more substantial effect.
Algal blooms: There have been suggestions that carp may increase the likelihood of algal blooms by preying on animals that eat algae, stirring up nutrients trapped in bottom sediments, damaging aquatic plants, and reducing plant growth via greater turbidity.
However, carp densities may have to be very high to significantly increase the likelihood of an algal bloom.
Erosion: Carp feeding habits can undermine river banks leading to the collapse of banks and vegetation.
However, clearing of riparian vegetation, changes to river flows through river regulation, and trampling by livestock are more important factors in bank erosion. Restoration of riparian vegetation can minimise the risk of damage by carp.
Impacts on invertebrates: Juvenile carp feed mainly on zooplankton, but start consuming larger (macro-) invertebrates once they reach around 15 cm in length. There is strong evidence that carp impact on native invertebrates in still waters, but only anecdotal evidence for running waters.
Impacts on aquatic plants: Carp have significant effects on native aquatic plants both through direct grazing and through uprooting plants while feeding, leading to a reduction in plant density and biomass. Soft-leaved, shallow-rooted and submerged plants are most likely to be affected.
Disease: In other parts of the world, carp have been associated with the distribution of a range of parasites and fungal, bacterial and viral diseases. However, there have been few disease outbreaks attributed to carp in Australia.
Reduction in native fish numbers: The effects of carp on native fish are not well understood. Negative impacts of carp are thought to include competition for food and habitats and effects on recruitment (population replenishment). However, many native species (such as golden perch, Murray cod, silver perch and freshwater catfish) had experienced well-documented declines even before carp became widespread.
The feeding methods of carp can uproot aquatic vegetation and muddy the water. Carp have been blamed for damaging freshwater habitats and causing decreases in light penetration, dissolved oxygen and plant material. These changes may have affected native fish.
What is NSW DPI doing?
In NSW, a Carp Assessment and Reduction Program has been developed to encourage the commercial utilisation of wild carp and promote and coordinate community carp control efforts.
This program has involved encouraging inland commercial fishers to harvest carp; supporting recreational carp fishing competitions; researching carp control methods; researching the distribution of carp in NSW; and providing education programs for community groups.
In addition, carp are listed as a Class 3 noxious species in NSW under the noxious species provisions of the Fisheries Management Act 1994.
NOTE: Unlike Class 1 and 2 species - which pose greater degrees of threat to the aquatic environment and are subject to different rules - Class 3 species may still be kept in aquaria, garden ponds and farm dams, and may still be bought and sold. However, an education and awareness campaign will be carried out to discourage their possession and sale, particularly in the coastal rivers where carp are not yet established.
This listing recognises the fact that keeping the colourful koi carp strains in garden ponds and aquaria is a popular pastime. At the same time, koi which escape into the wild quickly revert to the common (non-colourful) wild strain, and it is vital to stop the spread of this significant pest into new areas.
Carp have also been listed as a noxious species in Victoria and Queensland, a declared exotic species in South Australia, and a controlled fish in Tasmania. Their importation is prohibited by the Commonwealth government.
At a national level, a National Management Strategy for Carp Control has been developed by the Carp Control Coordinating Group (CCCG), which was established following an agreement between several government bodies including the Murray-Darling Basin Commission. The CCCG consists of state, territory and federal representatives and coordinates nation-wide research and management responses.
Research is also being undertaken into innovative ways of controlling carp populations. One method that offers promise in the long term (for use in conjunction with other control measures) is the 'daughterless carp' technology. This technology involves manipulating the genes of carp to produce an inheritable 'daughterless carp' gene which prevents fish from developing as females. This would result in fewer and fewer females being produced each generation until the carp population was mostly male. It is predicted that this could greatly reduce carp numbers within 20-30 years of its release. However, the technology needs to be further developed and thoroughly tested (e.g. to ensure it is safe) before it can be released.
How can you help?
- Only keep koi in places (garden ponds and other outdoor containers) where they cannot escape into natural waterways.
- Remember that it is illegal to stock carp into streams, rivers or lakes in NSW and fines of up to $11,000 apply.
- Do not use live carp as bait. The use of live carp as bait in freshwater is illegal and carries a high probability of infesting new areas with carp.
- Ensure your boat and trailer are free of weed before re-launching to avoid the possibility of spreading carp eggs and juveniles.
- Assist efforts to restore our rivers (which can help native fauna to out-compete carp) by taking part in a Rivercare, Landcare or Waterwatch project.
- Manage your land in a way that reduces damage to natural waterways, for example by restricting stock access to stream banks and conserving or restoring riparian vegetation.
- Take part in native fish restocking programs with your local angling group, and support recreational fishing for carp in your area.
- Support the commercial harvesting of carp by purchasing products such as carp-based fertilisers or pet food.
- Report any sightings of carp outside their known distribution to your local NSW DPI Office.
References
Braysher M. (2000). Ranking Areas for Action: A Guide for Carp Management Groups. Murray-Darling Basin Commission, Canberra.
Carp Control Coordinating Group. (2000). Future Directions for Research into Carp. Murray-Darling Basin Commission, Canberra.
Carp Control Coordinating Group. (2000). National Management Strategy for Carp Control 2000-2005. Murray-Darling Basin Commission, Canberra.
Gehrke PC, Harris JH. (1994). The role of fish in cyanobacterial blooms in Australia. Australian Journal of Marine and Freshwater Research 45: 905-915.
Harris JH, Gehrke PC. (Eds) (1997). Fish and Rivers in Stress: The NSW Rivers Survey. NSW Fisheries Office of Conservation and the Cooperative Research Centre for Freshwater Ecology, in association with the NSW Resource and Conservation Assessment Council, Cronulla.
Koehn J, Brumley A, Gehrke P. (2000). Managing the Impacts of Carp. Bureau of Rural Sciences, Canberra.
Koehn J. (2001). Carp - A Major Vertebrate Pest in Australia. Proceedings of the 12th Australasian Vertebrate Pest Conference, May 2001, Melbourne.
Mackenzie R, Bryant M. (2001). Controlling Exotic Pest Species in Queensland: A Strategic Approach. Proceedings of the 12th Australasian Vertebrate Pest Conference, May 2001, Melbourne.
National Carp Task Force. (2001). Carp: Villains or Victims. National Carp Task Force, Sydney.
Roberts J, Tilzey R. (Eds) (1996). Controlling Carp: Exploring the Options for Australia. Proceedings of the Workshop 22-24 October 1996, Albury. CSIRO Land and Water, Griffith.
Stuart I, Jones M, Koehn J. (2001). Targeting Spawning Habits to Control Carp Populations. Proceedings of the 12th Australasian Vertebrate Pest Conference, May 2001, Melbourne.