Most reach 45-60 cm in a UK garden pond, and well-kept Japanese bloodlines can exceed 80 cm.

How deep should a koi pond be?

At least 1.2 m over most of the surface, so the water stays cool in summer and does not freeze to the bottom in winter.

Can koi be kept in an aquarium?

Only as a short-term grow-on for young fish. Adults need pond volumes and there is no aquarium substitute.

Do koi need feeding in winter?

No. Stop feeding below roughly 8 C — koi cannot digest food properly at those temperatures and uneaten food fouls the pond.

How many koi can a pond hold?

A common working guide is around 1,000 litres of well-filtered water per adult koi, with filtration sized generously rather than to the minimum.

Koi (Cyprinus carpio) illustrated in its natural habitat — AI-generated illustration for OneShoal

PondPondIntermediate

Koi

Cyprinus carpio

The ornamental form of the common carp: a large, long-lived, sociable pond fish bred for colour and pattern over centuries in Japan.

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Ideal Conditions

Temperature: 4 – 24 °C
pH range: 7 – 8.5
Hardness: 6 – 20 dGH
Adult size: 45 – 90 cm
Min. pond size: 10,000 litres+
Min. depth: 120 cm
Lifespan: 25 – 50 years
Diet: Omnivore
Water flow: Moderate, well circulated and aerated
Preferred setup: Outdoor pond with heavy filtration, 1.2 m depth and shade

About the Koi

Koi are domesticated carp selected for the pattern and quality of their colouring rather than for any biological difference. They routinely exceed 45 cm and can live for decades, so a koi pond is a long-term structural commitment rather than an aquarium project. They are not aquarium fish at any stage beyond a temporary grow-on.

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Is it right for your tank?

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Where Koi comes from

Native range

East Asia (ancestral wild carp), Domesticated in Niigata, Japan

Countries / regions

Japan, China

Habitat

The ancestral carp lives in slow, warm lowland rivers, lakes and floodplains with soft bottoms and dense plant growth.

Koi are an ornamental domesticated form, so 'native range' refers to the wild ancestor rather than to koi themselves.

Similar species

Goldfish
Carassius auratus
Shubunkin
Carassius auratus (Shubunkin)
Golden Orfe
Leuciscus idus

We’re adding more full species guides as the catalogue grows.

Compatible tank mates

Reviewed guidance based on this species' recorded traits.

View all compatibility

Grass Carp
Ctenopharyngodon idella
Compatible in principle, but keeping this species is restricted or licensed in parts of the UK. Check the rules for your area before considering it.
Insufficient information
Golden Orfe
Leuciscus idus
Active surface-shoaling pond fish that shares coldwater parameters and needs the same high oxygen levels.
Great
Goldfish
Carassius auratus
Classic pond companion with the same temperature tolerance, though it is out-competed at feeding time by large koi.
Great
Sturgeon
Acipenser spp.
Only in very large, cool, strongly oxygenated ponds — sturgeon need sinking food that koi hoover up first.
Compatible with caution
Betta
Betta splendens
Tropical indoor species; koi pond temperatures would be fatal to it.
Not recommended

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Koi