Taxonomy & naming
Linnaeus described Cyprinus carpio in 1758, with the type locality given as Europe. The Catalog of Fishes treats it as the valid name for the European and western Asian carp. East Asian carp, long included in the species, are now often placed in C. rubrofuscus, and koi and farmed carp are variously assigned. Wild populations of the Danube and the Black, Caspian and Aral sea basins are the reference for the species in its natural range.
Morphology
A large, deep-bodied cyprinid with a long dorsal fin, a stout serrated spine at the front of the dorsal and anal fins, and two pairs of barbels at the mouth. Fully scaled wild fish are olive to bronze above and paler below. Domesticated forms include mirror and leather carp with few or no scales, and coloured koi. FishBase gives a maximum of 51 in TL, and fish of tens of kilograms are reported.
Habitat
It lives in lowland rivers, backwaters, floodplains and lakes with soft bottoms and vegetation, tolerating warm, turbid and low-oxygen water and surviving winters under ice. FishBase gives a temperature range of 37–95 °F, pH 6.5 to 9 and hardness of 10 to 15 dH. It occurs naturally in the Danube and the rivers of the Black, Caspian and Aral basins, and has been introduced very widely.
Feeding
Omnivorous and benthic. Carp take insect larvae, worms, molluscs, crustaceans, seeds and plant matter by rooting in the bottom, which muddies the water and damages vegetation.
Mating
Spawning is seasonal in late spring and summer. Groups of males accompany a female over flooded vegetation in shallows, with much splashing as eggs are shed.
Breeding
Eggs are sticky and attach to plants, with no parental care. Carp are bred commercially in ponds and with hormone induction. Fry feed on zooplankton.
In the aquarium
It is not an aquarium species. Stock is kept in ponds, where it needs a large volume, deep water and strong filtration, and it will dig up plants. Listings under the scientific name are for ornamental or pond stock; koi and mirror carp are normally sold by variety name.
Conservation
The IUCN Red List category is Least Concern, assessed in 2022. Within the native range, wild populations have declined, with hybridisation with and replacement by domesticated stock as a main threat. As an invasive fish the species is also a damaging introduction in many regions.