Quick answer
Koi are colorful ornamental carp bred for decoration and kept in garden ponds and water gardens around the world. Developed in Japan from common carp, they come in many color patterns and can grow 60 to 90 cm (2 to 3 ft) long. Hardy and long-lived, well-kept koi commonly reach 25 to 35 years and sometimes far longer.
Key takeaway
Koi are colorful ornamental carp bred for decoration and kept in garden ponds and water gardens around the world. Developed in Japan from common carp, they come in many color patterns and can grow 60 to 90 cm (2 to 3 ft) long. Hardy and long-lived, well-kept koi commonly reach 25 to 35 years and sometimes far longer.
Overview
Koi are colorful ornamental carp bred for decoration and kept in garden ponds and water gardens around the world. Developed in Japan from common carp, they come in many color patterns and can grow 60 to 90 cm (2 to 3 ft) long. Hardy and long-lived, well-kept koi commonly reach 25 to 35 years and sometimes far longer.
Biology
Koi (Cyprinus rubrofuscus) is classified as Fish with conservation status Least Concern. Typical weight about 5 kg; lifespan around 25–35 years, sometimes much longer.
Ecology
Diet: Omnivore. Habitat: Garden ponds; wild carp in rivers and lakes. Movement and social systems reflect those pressures.
People and this species
Learn before you travel or keep related pets. Wild individuals are not toys; captive care needs species-specific husbandry.
Further reading
See the full Koi profile for FAQs, taxonomy, and related guides on this site.
Behavior and intelligence
Koi are social, calm fish that often become tame enough to be hand-fed and to recognize the people who care for them. They are bottom-feeders that browse along the floor of a pond and gather at the surface at feeding time. In cold weather they slow down and rest near the pond bottom, becoming sluggish until the water warms again.
Diet and feeding
Koi are omnivores that eat a wide range of foods, including algae, plants, insects, worms, and prepared koi pellets. Keepers often feed high-protein food in warm months and reduce feeding as temperatures drop, since the fish digest slowly in cold water. Overfeeding and poor water quality are common problems in ponds.
Origins and varieties
Koi were developed in Japan beginning in the 1800s, when farmers selected colorful mutations of common carp raised for food. Today there are many named varieties distinguished by color, pattern, and scale type, and prized show koi can sell for very high prices. Their wild ancestor, the East Asian carp, lives in rivers and lakes across East Asia.
Care and longevity
Koi are hardy fish that can live for decades in a well-maintained pond with clean, oxygenated water and enough space to grow. They are famous for their long lifespans, and some individuals have reportedly lived well past 50 years. Predators such as herons and raccoons, along with poor water quality, are the main risks to pond koi.
Research notes
Figures for kois (Cyprinus rubrofuscus) come from field studies, museum records, and conservation assessments that do not always agree on exact averages. Prefer ranges over single-point claims, and check whether a source describes wild, captive, or mixed populations.
Practical takeaways
If you encounter kois in the wild, prioritise distance and local guidance. If you care for related domestic or captive animals, match diet and housing to species needs rather than generic pet advice. Share accurate status information (Least Concern) when discussing conservation.
Sources
FAQs
Koi: Key Facts & Natural History?
Koi are colorful ornamental carp bred for decoration and kept in garden ponds and water gardens around the world. Developed in Japan from common carp, they come in many color patterns and can grow 60 to 90 cm (2 to 3 ft) long. Hardy and long-lived, well-kept koi commonly reach 25 to 35 years and sometimes far longer.
What is the scientific name of the koi?
Cyprinus rubrofuscus
What do kois eat?
Omnivore
Where do kois live?
Garden ponds; wild carp in rivers and lakes
Are kois endangered?
Listed here as Least Concern. Check IUCN and national lists for the latest assessment.