European regional assessment: Near Threatened (NT)
EU 27 regional assessment: Near Threatened (NT)

In the European region, this species does not approach the range thresholds for Vulnerable under Criterion B (extent of occurrence (EOO) < 20,000 km², area of occupancy (AOO) < 2,000 km²) or D2. The population size does not approach the thresholds for Vulnerable under Criterion C (< 10,000 mature individuals) or D1, and there exists no quantitative analysis of extinction probability which would permit application of Criterion E.

Although no region-wide population trend data exists, it is plausible that a suspected past reduction based on a decline in AOO and the effects of introduced taxa falls within the threshold for Vulnerable under Criterion A2 (≥ 30% over the past 45 years = three generations).

As a result of this data uncertainty, Least Concern and Vulnerable are equally plausible Red List categories for the present assessment, therefore the Eurasian Carp is assessed as Near Threatened for both Europe and the EU 27 member states.

In the European region, this species is native to most rivers draining to the northern and western Black Sea and Sea of Azov basins, plus the Volga and upper Ural River systems in the Caspian Sea basin, and possibly northeastern Greece. Outside of Europe it is native throughout the remainder of the Black, Azov and Caspian basins, plus the Aral Sea basin.

It has been introduced outside of its natural range on a more-or-less pan-global basis alongside a number of congeneric species, particularly Amur Carp (Cyprinus rubrofuscus).

There is strong evidence to suggest that the Eurasian Carp was first introduced to the Mediterranean region centuries ago, possibly dating back to Greco-Roman times. More recently, hybrids and genetically-altered individuals have been translocated to all major continents, where they have been widely released into natural waters (see 'Use and Trade'). They are universally referred to as "Common Carp" or "Carp" despite their disparate and often uncertain ancestral origins. Neither an accurate description nor map of the Eurasian Carp's non-native range could therefore be produced within the scope of this assessment.

Common Carp are ranked among the most invasive freshwater fishes globally. In North America, Australia, and increasingly other areas outside their native ranges, they may dominate fish communities, are regarded as nuisance species, incur significant economic costs, and management efforts are directed toward control and eradication. Elsewhere, e.g. central and western Europe, United Kingdom, they are viewed as "naturalised" posing little or no threat to native aquatic communities, and continue to be extensively stocked.

This species' regional population size is unknown, but it is understood to significantly exceed 10,000 mature individuals. The current population trend has not been quantified, the number of subpopulations is unknown, and the genetic structure of the native population is poorly understood.

A significant reduction in population size is suspected to have occurred throughout its European range as a result of declining habitat quality and introgression with domesticated Common Carp (see 'Threats'). However, it is unclear how many non-introgressed subpopulations remain since exhaustive genetic screening has not been completed. It may have been extirpated from northeastern Greece.

Outside of the European range, large subpopulations apparently remain in the Caspian Sea basin, where introductions of domestic strains have been limited, and in three small lakes of northwestern Republic of Türkiye. The situation in the Black, Azov and Aral sea basins is less clear.

This comparatively large-bodied species naturally inhabits lentic and sluggish lotic habitats with relatively deep water and beds of aquatic vegetation, such as lowland river channels, floodplains and large natural lakes. It is eurytopic, and able to breed prolifically in artificial lakes, ponds, canals and irrigation ditches, while tolerating a wide range of temperatures and oxygen concentrations.

It is primarily an omnivorous benthivore, feeding on aquatic invertebrates and other zoobenthos by sucking in mouthfuls of sediment and ejecting the unsuitable material. Organic detritus and plant material are also consumed, including the stalks, leaves and seeds of both aquatic and terrestrial vegetation. Its foraging activity typically drives nutrient release from the substrate, and in a well-functioning ecosystem this can enhance phytoplankton productivity, accelerate nutrient fluxes and benefit organisms occupying higher trophic levels, including other fish species.

However, if the biomass of adult Eurasian or Common Carp individuals reaches a critical threshold for a given aquatic system there can be serious adverse effects, leading to significant changes in ecosystem community structure and an overall loss of biodiversity. Submerged aquatic vegetation may be uprooted or consumed, inorganic and organic solids from the sediment resuspended, and the fish can excrete large quantities of nutrients into the water column, which can drive deleterious shifts in phytoplankton production and community structure. Such consequences are typically evident in the conversion of shallow, clear-water, macrophyte-dominated lakes and ponds to turbid, unvegetated habitats with increased eutrophication rates. These degraded habitat conditions negatively affect the abundance and richness of native fishes, especially sight predators, thus driving homogeneity in fish communities. In addition, there exists experimental evidence that carp-dominated water bodies are considerably less attractive to waterfowl and other wetland birds.

Research had also demonstrated that Cyprinus species can play a significant role in driving biodiversity loss through predation of fish and amphibian eggs and larvae, dragonfly and other aquatic invertebrate larvae. This suggests that they occupy a dual position in terms of lake and pond community structuring, acting both as bottom-up ecosystem engineers and top-down predators. When present in sufficient numbers, they are therefore likely to induce dramatic biodiversity decline independent of the advancement of the eutrophication process or prior to ecosystem shift to a turbid state.

The Eurasian Carp is long-lived and can reach at least 50 years of age. Within the native range male individuals attain sexual maturity between three to five years of age, and females between four to six years. The generation length is unclear, but is at least 10-15 years. Spawning occurs in late spring (usually May-June, when water temperatures reach 17-18°C) along shallow shorelines, backwaters and in floodplains, and adults may migrate considerable distances in search of suitable habitat. It is a highly fecund, fractional (i.e. females release batches of eggs at intervals during the reproductive period) spawner, and fully-mature females can release as many as 2,000,000 eggs per year. These are released among dense vegetation, with individual females typically pursued by several males which compete to fertilise them. Upon contact with water, the eggs become adhesive and swell three to four times in volume. Hatched fry initially stick to the substrate until their yolk sacs are absorbed, and remain in warm, shallow, marginal habitats during the initial growth period.

It is important to note that much of the available information regarding the biology of Eurasian Carp is based on studies of feral populations comprising domesticated fish. The ancestral wild phenotype possesses a more elongate overall shape than the typically deep-bodied domestic strains, and may be more specialised in terms of habitat requirements and other aspects of life history. For example, in the Black and Caspian Sea basins there is evidence that some subpopulations are semi-anadromous, with adults inhabiting brackish water and migrating from the sea to adjacent rivers or coastal areas to spawn. These traits could feasibly render non-hybrid wild subpopulations more susceptible to anthropogenic habitat modification.

This species is threatened by genetic introgression with domestic Common Carp strains, which have been introduced throughout much of its native range. Uncontrolled and sometimes unauthorised restocking with these strains continues in many areas, and the extent of introgressive hybridisation with wild subpopulations is believed to be high.

Extensive habitat modification has also occurred throughout the Eurasian Carp's range. In particular, damming of lowland river channels has blocked annual migration routes, while canalisation and floodplain drainage has significantly reduced the extent of available spawning grounds (see 'Habitats and Ecology').

The combined effect of these threats on the Eurasian Carp population has not been investigated in detail, although a number of authors have commented on their plausibly adverse impact.

Cyprinus species were probably the first freshwater fishes exploited for aquaculture. Evidence from China dates back to ca. 6,000 BC, while in Europe the Eurasian Carp has been cultured for at least 2,000 years.

Today, they rank among the most commercially-important freshwater food fishes with global fishery and aquaculture production increasing by 35% to c. 3.9 million tonnes in the ten years from 2009-2019 according to FAO data. Aquaculture provides more than 95% of this volume, and Common Carp production occurs in more than 80 countries. China is the largest supplier, producing more than 70% of the global total, while in some European countries (e.g., Czech Republic, Poland), Common Carp account for more than 80% of total fish production. The majority of hatchery-raised individuals comprise hybrids of mixed and often uncertain genetic origin.

As a result of this widespread, long-term exploitation, a number of domesticated strains of Common Carp were developed due to contrasting aquaculture management strategies in different geographical regions. These include three with reduced scale cover, commonly referred to as 'mirror' (scattered scales), 'linear' (with a single row of scales along the side of the body), and 'leather' (entirely scaleless) carp, respectively.

A number of classic methods have been used in attempts to increase productivity and breeding efficiency, including hybridisation, crossbreeding, chromosomal manipulation and selective breeding. Targeted traits have included improved growth rates, manipulation of body shape, and resistance to cold or disease, with varying degrees of success, while genetic techniques have focussed on artificial sex regulation, production of genetically sterile offspring and gene transfer. The majority of global production is still carried out using unselected strains, however, and organised programmes are based mostly on crossbreeding. Research has revealed low genetic diversity in domesticated strains compared with wild populations.

Domesticated strains of Common Carp have been translocated internationally since at least the 18^th century, and this process expanded intensively during the 20^th century. In numerous cases this has been followed by their subsequent release or escape into natural waters, including within the native range of the Eurasian Carp (see 'Threats').

In addition to their aquaculture value, Common Carp are also prized as sport fish with a high socioeconomic value, particularly in Europe and the United Kingdom, but also North America, Africa, and increasingly elsewhere. In some countries carp fishing represents an important branch of tourism and can provide alternative income pathways for commercially-managed fisheries. An international industry based on specialised tackle and techniques to catch large carp for recreational purposes has developed since the mid-20^th century. Where Common Carp have been stocked for angling purposes, they consist entirely of domesticated strains and are often repeatedly restocked using fish from a range of sources. This species is heavily-exploited by the recreational angling sector. It is among the most popular sports fishes in the world.

Contrary to popular understanding, the Eurasian Carp is not the parent species of the ornamental Koi (aka nishikigoi) Carp, which comprises a series of selectively-bred colour forms of the Amur Carp.

This species is not protected at the international scale, and no coordinated conservation management plan exists. Common Carp inhabit numerous protected areas, but it is unclear which, if any, of these comprise genetically pure Eurasian Carp.

In Croatia it is currently assessed as Endangered at the national level, and further stocking of domestic Common Carp strains is illegal throughout the country.

Some authors have suggested that refuge populations using genetically-pure fish from known locations should be established. To that end, field surveys designed to establish where non-introgressed subpopulations remain are recommended as a priority initial measure.