Common carp
The common carp, 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, but the species has also been domesticated and introduced into environments worldwide, and is often considered a positive invasive species, being included in the list of the world's 100 worst invasive species. It gives its name to the carp family, Cyprinidae.
Taxonomy
The type subspecies is Cyprinus carpio carpio, native to much of Europe.The subspecies Cyprinus carpio haematopterus, native to eastern Asia, was recognized in the past, but recent authorities treat it as a separate species under the name Cyprinus rubrofuscus. 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 ; 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. 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. In Europe, domestication of carp as food fish was spread by monks between the 13th and 16th centuries. The wild forms of carp had already reached the delta of the Rhine in the 12th century, probably with some human help. Variants that have arisen with domestication include the mirror carp, with large, mirror-like scales, the leather carp, and the fully scaled carp. Koi carp in Japanese, 鯉魚 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.
Physiology and life history
The carp has a robust build, with a dark gold sheen that is most prominent on its head. Its body is adorned with large, conspicuous scales that are very shiny. It has large pectoral fins and a tapering dorsal fin running down the last two-thirds of its body, getting progressively higher as it nears the carp's head. Its caudal and anal fins may either be a dark bronze or washed with a rubbery orange hue. Two or three spines are on the anal fin, the first being serrated, and the dorsal fin has three or four anterior spines, the first of which is also serrated. 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 can grow to a maximum length of, a maximum weight of over. The longest-lived common carp documented was of wild-origin, and was 64 years of age. The largest recorded carp, caught by British angler, Colin Smith, in 2013 at Etang La Saussaie Fishery, France, weighed. The average size of the common carp is around and.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. The ideal temperature is, with spawning beginning at ; they easily survive winter in a frozen-over pond, as long as some free water remains below the ice. Carp are able to tolerate water with very low oxygen levels, by gulping air at the surface.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, 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
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. Carp pick up sediment by generating suction and mouth the content to identify and select food items by taste and size. Gill rakers form a branchial sieve that may aid in food separation, but the carp is also able to clamp down on food items it detects using a muscular palatal pad and inferior postlingual organ. The sediment is passed back and forth between the mouth and pharynx repeatedly as food is found. The carp may end up spitting out sediment, 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.
Reproduction
An egg-layer, a typical adult female can lay 300,000 eggs in a single spawn. 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. Eggs and fry often fall victim to bacteria, fungi, and the vast array of tiny predators in the pond environment. Carp that survive to the juvenile stage are preyed upon by other fish such as the northern pike and largemouth bass, and several birds and mammals.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.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 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", while wild-type carp may have either SSnn or Ssnn genotype. The "S" locus has been identified as containing the gene encoding fibroblast growth factor receptor Fgfr1A1, which was duplicated during the course of carp evolution and consequently does not typically produce lethal phenotypes when only one locus is mutated. 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. Leather carp also have reduced numbers of red blood cells and slower growth rates than scaled carp. Mirror carp from Hungarian and Asian stocks have been observed to have fewer pharyngeal teeth than scaled carp, while nude carp had fewer still.
A population of mirror carp in Madagascar was found to have reverted to full scale cover after being introduced from France in the early twentieth century. The feral Malagasy carp still possessed large scales due to their mirror phenotype, but had increased scale coverage approaching that of wild-type carp. Hubert et al. found that the recessive allele at the "S" locus was still fixed in the population. They believe that the phenotypic reversion was due to compensation by quantitative trait loci as a result of a selective disadvantage for partial scaling in the wild, perhaps related to an impairment in parasite resistance.
Introduction into other habitats
Common carp have been introduced to most continents and some 59 countries. In absence of natural predators or commercial fishing, they may extensively alter their environments due to their reproductive rate and their feeding habit of grubbing through bottom sediments for food. In feeding, they may destroy, uproot, disturb and eat submerged vegetation, causing serious damage to food sources and habitats of native duck and fish populations.In 2020, scientists demonstrated that a small proportion of fertilized common carp eggs ingested by waterfowl survive passing through the digestive tract and hatch after being retrieved from the feces. Birds exhibit strong preference for fish eggs, while cyprinids produce hundreds of thousands of eggs at a single spawning event. These data indicate that despite the low proportion of eggs surviving the digestive tract of birds, endozoochory might provide a potentially overlooked dispersal mechanism of invasive cyprinid fish. If proven under natural circumstances, endozoochorous dispersal of invasive fish could be a strong conservation concern for freshwater biodiversity.