Koi

Looks how to spot one

Large scaled carp; also scaleless or partly scaled (Doitsu), metallic-scaled (Kinginrin) and long-finned (butterfly) forms

A big, sturdy, torpedo-shaped carp with a pair of barbels by the mouth. Koi are prized for the bold patterns on their backs, which are meant to be admired from above in a pond. Most have normal scales, but some lines have few or no scales, some have sparkling metallic scales, and butterfly koi have long, flowing fins.1

Personality what they are like

Peaceful and sociable pond fish. Koi soon learn who feeds them, gather at the edge at feeding time and can be trained to take food from a hand, which makes them rewarding to keep.1

Daily activity how busy a day looks

Strong swimmers that grow large, so they need a roomy, deep pond rather than an aquarium. They slow right down in cold water and eat very little in winter.12

Grooming and care the hands-on bits

Keep in a well-filtered, well-oxygenated pond with stable pH. Koi are most comfortable at about 15 to 25 C. Ponds should be at least 1 m deep in warm climates and 1.5 m or more where winters are harsh. Protect the pond from predators such as herons, kingfishers, otters, raccoons and cats, and avoid feeding when the water drops below about 10 C.1

Home where they are happiest

An outdoor garden pond with good filtration and aeration and enough depth to stay frost-free at the bottom in winter. Their wild ancestor, the Amur carp, lives in slow-flowing rivers and lakes around 2 m deep.14

Food basics what goes in the bowl

Omnivorous bottom feeders. A quality pellet diet can be topped up with treats such as peas, lettuce and watermelon. Feeding is reduced as the water cools and paused in cold water.14

Company who they like around

Sociable fish that are usually kept as a group in a shared pond, where they feed and move around together.1

The story where it all began

Carp were first kept as a food fish, and odd single-coloured carp appeared by chance in China and Japan long before anyone bred them on purpose. Deliberate breeding of coloured carp began in the 1820s in the snowy mountain villages of the Nijumurago area of Niigata, where farmers raised carp in rice-terrace ponds. Red-and-white fish came first, and colourful koi grew popular enough by 1875 that the trade was briefly banned as speculation before being allowed again. The name nishikigoi, meaning brocaded carp, came into use around 1910, and a display at the 1914 Tokyo Taisho Exposition, where koi won a silver medal, brought them national fame. The Kohaku and Taisho Sanshoku varieties were fixed by 1917 and Showa Sanshoku by 1927. During the 20th century the hobby spread worldwide, long-finned butterfly koi were developed in the 1980s, and in the 21st century collectors from across Asia have bought top fish from Niigata breeders.12

Recognised by the official bits

Zen Nippon Airinkai (All Japan Nishikigoi Promotion Association)

Japanese association that promotes nishikigoi, trains judges and runs the International Koi Show5

British Koi Keepers Society

UK national body supporting local koi clubs6

Japan Agricultural Heritage

Niigata's rice farming and carp-rearing system, the home of nishikigoi, was recognised as a Japan Agricultural Heritage site in 20172