Koi

Care at a glance

Koi are not aquarium fish but pond animals, and that is the first thing to know. A full-grown koi easily reaches seventy to eighty centimetres and can outlive most pets — fifty years is not exceptional. Young koi in an indoor tank is a stopgap, not a destination.

In the pond it is all about filter capacity and oxygen: koi produce a lot of waste and are sensitive to nitrite. They eat virtually every water plant and uproot the rest, so a planted pond and koi go badly together. They handle northern winters fine as long as the water is deep enough and a hole is kept open in the ice; through those cold months you do not feed.

Good to know

• Outgrows most home tanks
• Eats or uproots live plants

Related species

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