FaunaHub

Koi (Cyprinus carpio)

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Colourful koi carp swimming in a garden pond.

Koi — ornamental varieties of the common carp (Cyprinus carpio).

Image: Bernard Spragg. NZ, CC0, via Wikimedia Commons.

Overview

Koi are ornamental varieties of the common carp (Cyprinus carpio), selectively bred in Japan and elsewhere for striking colours and patterns. They are classic ornamental pond fish, valued for their beauty and longevity. Although they descend from the same species as wild and farmed carp, koi are bred purely for appearance. They are large, long-lived fish and a serious long-term responsibility.

Habitat & Range

Koi are kept in outdoor ponds and water gardens rather than the wild, though their carp ancestors live in fresh waters across Eurasia. A suitable koi pond needs to be large and deep enough for big fish, with strong filtration and stable water quality. Koi are coldwater fish that can overwinter in suitable ponds in many climates. Released koi can become invasive, so they should never be put into local waterways.

Diet

Koi are omnivores that forage for plants, invertebrates, and organic matter and are fed prepared pond foods in captivity, with feeding often reduced or stopped in cold weather when their metabolism slows. This page does not give feeding quantities; appropriate diet and amounts depend on the fish, season, and water temperature and should follow qualified guidance.

Behavior

Koi are social, generally peaceful fish that are active in warmer water and slow down as temperatures fall. Many become accustomed to their keepers and may feed at the surface. They can live a long time and grow large, so their behaviour and needs change as they mature. Good water quality is central to their health.

Human Interaction & Conservation

Koi have deep cultural significance, especially in Japan, and koi keeping is a long-established hobby. They are ornamental pond animals, not wildlife; releasing them is harmful and often illegal. Responsible keeping means an adequately sized, well-filtered pond, a long-term commitment to maintenance, and qualified help if a fish appears unwell. This profile is educational and not a substitute for pond-care or veterinary advice.

Appearance & Recognition

Koi are large, torpedo-shaped carp that can reach substantial sizes. They are bred in many named colour varieties — combining white, red, orange, yellow, black, blue, and metallic tones in distinctive patterns. Some have barbels at the mouth like other carp. The variety and quality of colouration are central to how koi are appreciated by enthusiasts.

Similar Animals

Koi are the same species as the common carp covered separately on FaunaHub and are close relatives of the goldfish. They are sometimes confused with large goldfish, but koi grow much bigger, usually have barbels, and are kept in ponds rather than aquariums.

Aquarium & pond care hub →

More photos of the koi

A common carp, the wild ancestor of koi.

A common carp (Cyprinus carpio), the species koi are bred from.

Image: George Chernilevsky, CC BY-SA 4.0, via Wikimedia Commons.

Frequently Asked Questions — Koi

Are koi and goldfish the same?
No. Both are ornamental carp-family fish, but koi are a colour-bred form of the common carp (Cyprinus carpio) and grow much larger, while goldfish are a different species (Carassius auratus). Koi also typically have barbels at the mouth, which goldfish lack.
How big do koi get and how long do they live?
Koi can grow large and are long-lived, often living for many years or even decades in well-maintained ponds. Exact size and lifespan depend heavily on genetics, pond size, and water quality, so figures should be treated as general rather than guaranteed.
Can koi live in a small pond or tank?
Koi need substantial, well-filtered space because they grow large and produce a lot of waste; small ponds or tanks are generally unsuitable for adult koi. Specific pond requirements should follow qualified guidance — keeping koi is a long-term commitment.

Sources and further reading

Authoritative wildlife references used for general educational context. Conservation status should always be verified against current IUCN Red List data. External links open in a new tab.