thumb|Painting by Ellen Edmonson
The common carp (Cyprinus carpio), also known as European carp, Eurasian carp, or simply carp, is a widespread freshwater fish of eutrophic waters in lakes and large rivers in Europe and Asia. The native wild populations are considered vulnerable to extinction by the International Union for Conservation of Nature (IUCN),
The subspecies Cyprinus carpio haematopterus (Amur carp), native to eastern Asia, was recognized in the past, The common carp and various Asian relatives in their pure forms can be separated by meristics and also differ in genetics, but they are able to interbreed. Common carp can also interbreed with the goldfish (Carassius auratus); the result is called Kollar carp. Another artificial hybrid is ghost carp, which is bred between common carp and Japanese Purachina koi. The large variations of colours produced make ghost carp a popular commercial species.
History
The common carp is native to Europe and Asia, and has been introduced to every part of the world except the poles. They are the third-most frequently introduced fish species worldwide, and their history as a farmed fish dates back to Roman times. Carp are used as food in many areas, but are also regarded as a pest in several regions due to their ability to out-compete native fish stocks. The original common carp was found in the inland delta of the Danube River about 2000 years ago and was torpedo-shaped and golden-yellow in colour. It had two pairs of barbels and a mesh-like scale pattern. Although this fish was initially kept as an exploited captive, it was later maintained in large, specially built ponds by the Romans in south-central Europe (verified by the discovery of common carp remains in excavated settlements in the Danube Delta area). As aquaculture became a profitable branch of agriculture, efforts were made to farm the animals, and the culture systems soon included spawning and growing ponds. The common carp's native range also extends to the Black Sea, Caspian Sea, and Aral Sea.
Both European and Asian subspecies have been domesticated. Variants that have arisen with domestication include the mirror carp, with large, mirror-like scales (linear mirror – scaleless except for a row of large scales that run along the lateral line; originating in Germany), the leather carp (virtually unscaled except near dorsal fin), and the fully scaled carp. Koi carp (錦鯉 (nishikigoi) in Japanese, 鯉魚 (pinyin: lĭ yú) in Chinese) is a domesticated ornamental variety that originated in the Niigata region of Japan in the 1820s, but its parent species is likely the East Asian carp, possibly C. rubrofuscus. and the dorsal fin has three or four anterior spines, The mouth of the carp is downward-turned, with two pairs of barbels, one pair at the corners of the upper lip, and the other on the lower. Wild common carp are typically slimmer than domesticated forms, with body length about four times body height, red flesh, and a forward-protruding mouth. Common carp can grow to very large sizes if given adequate space and nutrients. Their average growth rate by weight is about half the growth rate of domesticated carp. They do not reach the lengths and weights of domesticated carp, which (range, 3.2–4.8 times) The largest recorded carp, caught by British angler, Colin Smith, in 2013 at Etang La Saussaie Fishery, France, weighed .<!-- repeat The wild, non-domesticated forms tend to be much less stocky at around 20%–33% the maximum size.--> The average size of the common carp is around and .
thumb|300px|The [[skeleton of a European carp]]
thumb|300px|European carp [[x-ray]]
Habitat
Although tolerant of most conditions, common carp prefer large bodies of slow or standing water and soft, vegetative sediments. As schooling fish, they prefer to be in groups of five or more. They naturally live in temperate climates in fresh or slightly brackish water with a pH of 6.5–9.0 and salinity up to about 0.5%, and temperatures of .
Diet
Common carp are omnivorous. They can eat a herbivorous diet of aquatic plants, plant tubers, and seeds, but prefer to scavenge the bottom for insects, crustaceans (including zooplankton and crawfish), molluscs, benthic worms, fish eggs, and fish remains. Common carp feed throughout the day, with the most intensive feeding at night and around sunrise.
Feeding mechanisms
thumb|22 inch long common carp
Common carp are benthic feeders and root in sediment for food items. Their barbels may help to feel for food embedded in the sediment, like plant tubers or annelids. which contributes to water turbidity.
While common carp have no oral teeth, 10 pharyngeal teeth are used for crushing or grinding food. The carp has no stomach, and the intestinal length can vary based partially on dietary composition in early life. Although carp typically spawn in the spring, in response to rising water temperatures and rainfall, carp can spawn multiple times in a season. In commercial operations, spawning is often stimulated using a process called hypophysation, where lyophilized pituitary extract is injected into the fish. The pituitary extract contains gonadotropic hormones, which stimulate gonad maturation and sex steroid production, ultimately promoting reproduction.
Predation
A single carp can lay over a million eggs in a year. and mammals (including otter and mink).
Salinity
Common carp are quite salt tolerant compared to other types of freshwater fish, research studies showed that they can withstand salinity of at least 12 g/L (12 ppt).
Mirror carp
thumb|A mirror carp
Mirror carp, regionally known as Israeli carp, are a type of domesticated fish commonly found in Europe but widely introduced or cultivated elsewhere. They are a variety of the common carp (Cyprinus carpio) developed through selective breeding. The name "mirror carp" originates from their scales' resemblance to mirrors.
Genetics
The most striking difference between mirror and common carp is the presence of large, mirror-like scales on the former. The mirror-scale phenotype is caused by a genetic mutation present at one of two scale trait loci, denoted by their S and N alleles, respectively. The genotype that produces a mirror scale phenotype is "ssnn" (all recessive), while wild-type carp may have either SSnn or Ssnn genotype. The "N" locus has not been identified, but is hypothesized to have bearing on the development of embryonic mesenchyme.
Contrary to popular belief, a leather carp is not always a mirror carp without scales. Similar to mirror carp, leather, or "nude" carp, are homozygous recessive at the "S" locus, but unlike mirror carp, true leather carp are heterozygous for a dominant mutant allele at the "N" locus (ssNn genotype).