Koi Care Guide - Pond Setup, Feeding & Breeding

Koi are brightly patterned ornamental carp, prized for their bold red, white, black, yellow and metallic colour combinations. Their patterns are given traditional Japanese names, and individual fish can become recognisable long-term companions as they grow larger and develop more distinctive markings.

These are powerful, intelligent and highly active fish with a calm nature when kept in suitable surroundings. Koi often learn to associate people with feeding and may rise to the surface, although their constant activity can make them unsuitable for delicate planted aquariums or small community tanks.

In the wild, their carp relatives inhabit slow-moving rivers, floodplain lakes, ponds and other relatively calm freshwater environments. They are bottom-oriented foragers, using their sensitive mouths to search through mud, gravel and vegetation for edible organisms.

Koi have been selectively bred in Japan for centuries, producing many named varieties such as Kohaku, Sanke and Showa. Although often sold when only a few centimetres long, they are long-lived fish capable of reaching impressive proportions and becoming substantial pond inhabitants.

Koi are domesticated ornamental forms of the common carp complex, with their ancestry traced to carp from East Asia. The species Cyprinus rubrofuscus is native to parts of China and surrounding eastern Asian waters, while the familiar coloured varieties were developed extensively in Japan.

Koi are pond fish rather than conventional aquarium residents. A small group of adult Koi should have at least 5,000 litres, with substantially more space preferred as they mature; a pond around 3 metres by 2 metres with a depth of at least 1.2 metres is a more appropriate starting guideline than a standard aquarium. Use a smooth, fish-safe substrate or leave much of the base open, provide strong biological and mechanical filtration, reliable aeration, shade and some cover, and avoid sharp decor that could damage their bodies or barbels. A secure cover or suitable pond net may be needed to deter predators.

Up to about 90 cm (35 in) in total length, although many captive Koi remain closer to 50–75 cm (20–30 in). Females commonly grow larger and deeper-bodied than males.

Koi are omnivorous opportunistic feeders. Offer a high-quality Koi pellet as the staple, choosing a formulation appropriate to water temperature and the fish's age, and supplement it occasionally with foods such as peas, leafy greens, earthworms, prawns or other suitable aquatic invertebrates. Feed modest portions that are consumed promptly, since excess food rapidly affects pond water quality.

Suitable companions include other Koi and robust pond fish such as larger goldfish, tench and some weather loaches, provided the pond is spacious and well filtered. Avoid housing Koi with tiny fish, slow delicate species or highly territorial fish, since their size, feeding activity and tendency to stir the bottom can cause stress. Koi may also consume very small fish, fry and aquatic invertebrates.

Koi are egg-scattering spawners that usually breed in spring when temperatures rise and daylight increases. Provide mature females and several males with spawning brushes, fine-leaved plants or other surfaces for the adhesive eggs to cling to. Spawning can be vigorous, so use plenty of space and remove the adults or protect the eggs afterwards, as Koi readily eat both eggs and fry. The young hatch after several days and require very fine foods before gradually accepting larger fry diets.

Mature females are generally larger, broader and fuller through the abdomen, particularly before spawning. Males are usually slimmer and may develop rough breeding tubercles on the head and pectoral fins during the spawning season.