Some of the major colors are white, black, red, orange, yellow, blue, brown and cream, besides metallic shades like gold and silver-white ('platinum') scales.

Carp are coldwater fish, and their ability to survive and adapt to many climates and water conditions allowed the domesticated species to be propagated to many new locations, including Japan.

[5] In addition, pharyngeal teeth of all six subfamilies of the Cyprinidae family living in Japan today, including carp (Cyprinus), have been found at the Awazu lakebed site (粟津湖底遺跡) dating from the Middle Jomon Period (5500 – 4400 years ago).

), as well as the East Asian ancient lineage of wild common carp (C. carpio), previously proposed on the basis of fossil data.

[10] In the Japanese history book Nihon Shoki (Chronicles of Japan, 720), it is written that Emperor Keikō released carp in a pond for viewing when he visited Mino Province (present Gifu Prefecture) in the fourth year of his reign (74 AD).

[12] In addition, Hitomi Hitsudai's drug dictionary Honchō Shokkan (本朝食鑑, Japanese Medicine Encyclopedia, 1697) states that red, yellow, and white carp of the three colors were in Japan at that time.

[13] However, it is believed that these single-colored carp were not a variety created by artificial selection, as is the case with today's koi, but rather a mutation-induced color change.

The name Nishikigoi is said to have been given by Kei Abe, who was the chief fisheries officer of the Niigata Prefectural Government in the Taisho era (1912–1926), after he admired the Taishō Sanshoku when he first saw it.

In 1927, Shōwa Sanshoku (by Shigekichi Hoshino) was fixed as a breed, and in 1939, koi were exhibited at the Japanese pavilion at the Golden Gate International Exposition held in San Francisco.

[30] In particular, since the 21st century, some wealthy Chinese have imported large quantities of koi from Niigata in Japan, and the price of high-quality carp has soared.

[3] The koi are a group of breeds produced by artificial selection primarily from black carp called nogoi (野鯉, lit.

[33] Cyprinus haematopterus is thought to refer to the Amur carp of Eurasian origin, traditionally called Yamatogoi (大和鯉, lit.

Extensive hybridization between different populations, coupled with widespread translocations, has muddled the historical zoogeography of the common carp and its relatives.

However, they differ in meristics from the common carp of Europe and Western Asia,[16] leading recent authorities to recognize them as a separate species, C. rubrofuscus (C. c. haematopterus being a junior synonym).

[49] On the other hand, most ornamental koi breeds currently distributed worldwide originate from Amur carp (Cyprinus rubrofuscus) bred in Japan in the first half of the 19th century.

The bright colors of koi put them at a severe disadvantage against predators; a white-skinned Kōhaku is highly noticeable against the dark green of a pond.

Herons, kingfishers, otters, raccoons, skunk, mink, cats, foxes, and badgers are all capable of spotting out koi and eating them.

[48] A well-designed outdoor pond has areas too deep for herons to stand, overhangs high enough above the water that mammals cannot reach in, and shade trees overhead to block the view of aerial passers-by.

With proper care, they resist many of the parasites that affect more sensitive tropical fish species, such as Trichodina, Epistylis, and Ichthyophthirius multifiliis infections.

Some koi farms in Israel use the KV3 vaccine, developed by M. Kotler from the Hebrew University of Jerusalem and produced by Kovax, to immunise fish against KHV.

[62] Only biosecurity measures such as prompt detection, isolation, and disinfection of tanks and equipment can prevent the spread of the disease and limit the loss of fish stock.

In 2002, spring viraemia struck an ornamental koi farm in Kernersville, North Carolina, and required complete depopulation of the ponds and a lengthy quarantine period.

Although a koi breeder may carefully select the parents they wish based on their desired characteristics, the resulting fry nonetheless exhibit a wide range of color and quality.

However, unlike cattle, purebred dogs, or more relevantly, goldfish, the large majority of these offspring, even from the best champion-grade koi, are not acceptable as nishikigoi (they have no interesting colors) or may even be genetically defective.

These unacceptable offspring are culled at various stages of development based on the breeder's expert eye and closely guarded trade techniques.

While it requires diligent oversight to narrow down the favorable result that the breeder wants, it also makes possible the development of new varieties of koi within relatively few generations.

This makes waterways unattractive, reduces the abundance of aquatic plants, and can render the water unsuitable for swimming or drinking, even by livestock.

In some countries, koi have caused so much damage to waterways that vast amounts of money and effort have been spent trying to eradicate them, largely unsuccessfully.

[69] In many areas of North America, koi are introduced into the artificial "water hazards" and ponds on golf courses to keep water-borne insect larvae under control through predation.

[71] The custom of koinobori (carp streamers), which began in the Edo period (1603–1867), is still practiced today and displayed in gardens on Children's Day, 5 May.