Koi

About the koi

Koi are ornamental varieties of carp, bred for color and pattern rather than for food. The more precise term is nishikigoi, or "brocaded carp," and the fish themselves are a domesticated form of the Amur carp (Cyprinus rubrofuscus), a species long treated as a subspecies of the common carp but now classified separately by taxonomic authorities such as Eschmeyer's Catalog of Fishes.

Carp were originally domesticated in China for food, and the practice of farming them for consumption spread from there into Japan, where they were raised in ponds and rice paddies for centuries. Mutation-driven color changes in carp — red, blue, black, white, and yellow individuals — were recorded in both China and Japan long before anyone bred deliberately for color; those single-colored fish were naturally occurring variants kept alongside ordinary food carp, not a purpose-built variety.

Systematic breeding for color began in the 1820s in the Nijūmuragō area of Niigata Prefecture, which spans the towns of Ojiya and Yamakoshi on Honshu. Farmers there, breeding red and white koi and crossing them with black koi during the Bunka and Bunsei eras (1804–1830), eventually fixed the varieties recognized today. The most popular group, called Gosanke, is made up of three of these: Kōhaku, Taishō Sanshoku, and Shōwa Sanshoku. Koi are also classified by scale type — including fully scaled fish and the low-scaled "Doitsu," or German-carp, lineage — and by metallic colors such as gold and platinum.

Behavior and diet

Little in the historical record concerns koi behavior as distinct from other carp. Carp generally are coldwater fish, and their tolerance for a wide range of climates and water conditions is what allowed the domesticated form to spread from continental Asia into Japan and, eventually, into ponds worldwide. Villagers in the Nijūmuragō area raised carp in fallow rice fields as an emergency winter food supply, one of the reasons koi breeding flourished in that region in the first place.

Breeding for color, as opposed to breeding for size or hardiness, has always been a game of long odds. Even in modern koi farming, the share of offspring from a single spawning that come out with superior, sellable coloration is less than one percent, which helps explain why individual prizewinning koi can carry very high price tags — a single fish sold to a Chinese collector for about $2 million in 2018, the highest price ever recorded for one.

Range and habitat

Koi trace their ancestry to the Amur carp, native to East Asia, though genetic studies show Japan also has its own ancient native carp lineage, distinct from the Eurasian domesticated lineages introduced later. Ornamental breeding took root specifically in the Nijūmuragō area of Niigata Prefecture, on the northeastern coast of Honshu, where farmers kept carp in terraced ponds near rice paddies.

Today koi are not a wild population in any meaningful sense; they are raised and displayed in outdoor koi ponds and water gardens, a hobby that spread from Japan across the world over the twentieth century. Since the start of the 21st century, collectors — many from other parts of Asia — have imported large numbers of high-quality koi from Niigata, and prices for top fish have risen sharply as a result.

Conservation status

Koi are Not Evaluated (NE) on the IUCN Red List. They are a domesticated, selectively bred form of carp, and domestic animals aren't assessed on the Red List.

Their closest wild relative, the Amur carp, is farmed widely across East Asia as a food fish and has been raised in aquaculture there for at least two and a half thousand years. Because koi are bred deliberately for the ornamental trade rather than taken from the wild, the conservation concerns that affect many wild fish don't apply to them in the same way.