Koi

Cyprinus rubrofuscus

Also known as Nishikigoi, Cyprinus carpio, Japanese koi, Amur carp, Ornamental carp

FreshwaterFish

Koi (Cyprinus rubrofuscus) — Published by Zoologische Mededelingen, at http://www.zoologischemededelingen.nl . Creative commons license published on main page. · CC BY 3.0

Care at a glance

Temperature: 39–81°F (4–27°C)
pH: 7.0–8.5
Adult size: 23.6 in (60 cm)
Minimum tank: 264 gal (1,000 L)
Temperament: Peaceful
Social behavior: Social
Swim level: Bottom
Difficulty: Medium
Breeding: Medium
Rarity: Very common
Origin: Ornamental form of the Amur carp from East Asia, now kept in garden ponds worldwide after centuries of color breeding in Japan and China.
Family: Cyprinidae

Overview

Koi are pond fish, not aquarium fish. A single koi needs roughly 1000 litres to start, and a group needs a pond of several thousand litres with strong filtration, since they are big, messy eaters that grow past 60 cm. Keep them in groups in cool to temperate water from about 4 to 27 C and feed a varied omnivore diet of sinking koi pellets, greens, and occasional live or frozen foods. They mix well with goldfish and other large peaceful pond fish, but they uproot plants and eat anything small enough to swallow.

In the wild

Koi are domesticated color forms of the Amur carp, a hardy river and pond fish from East Asia. Wild ancestors live in slow rivers, lakes, and flooded fields with soft substrates they root through for food. They handle a very wide temperature swing, staying active in summer warmth and slowing to near dormancy under winter ice. Stable, well oxygenated, well filtered water matters far more than a narrow parameter target.

Good to know

Koi are usually sold under the old name Cyprinus carpio, but the ornamental strains trace to Cyprinus rubrofuscus, the Amur carp. Color breeding began in Japan in the 1800s and now covers dozens of named varieties such as Kohaku, Sanke, and Showa. Individuals can live for several decades and reach 60 cm or more in a large pond.