Fish
Koi Carp
Cyprinus rubrofuscus
Origin: Koi are an ornamental form of the East Asian (Amur) carp, developed in Japan from fish imported for food. Their ancestor inhabits slow rivers and ponds of East Asia. Modern koi are the result of centuries of selective breeding in pond farms.
Also known as: Nishikigoi, Brocaded carp, Cyprinus rubrofuscus
Fact sheet
- Size
- 60 cm
- Lifespan
- 30 years
- Minimum tank size
- 1000 L
- Temperature
- 2–30 °C
- pH
- 7–8.5
- Hardness GH
- 8–25 °dH
- Temperament
- Peaceful
- Social behavior
- Schooling
- Group size
- 4+ individuals
- Swimming zone
- Middle, Bottom
- Diet
- Omnivore
- Jumps out
- Yes
- Eats plants
- Yes
Overview
Koi are large coldwater pond fish famous for their bright patterned colours and their symbolism of luck and longevity in Japan. They are intelligent, calm, and very long-lived fish that recognise their owner and take food from the hand. Koi grow very large and are intended primarily for garden ponds, not aquariums. They need a huge volume of water, powerful filtration, and good aeration. With proper care they live for decades and become family pets.
Appearance
The body is powerful and elongated, usually 45–60 cm long, sometimes to 90 cm. Colour depends on the variety (nishikigoi grades): combinations of white, red, black, yellow, blue, and metallic form strictly classified patterns (Kohaku, Sanke, Showa, and others). Two pairs of barbels sit by the mouth. Sexual dimorphism is weak; females are fuller.
Care
A garden pond of at least 1000 L (ideally several tonnes) for a few fish, with powerful external filtration, aeration, and protection from overheating and freezing. Temperature 2–30 °C (a coldwater species, optimum 15–25 °C), pH 7.0–8.5, hardness GH 8–25. In an aquarium only juveniles can be kept temporarily. Large regular water changes are essential.
Feeding
An omnivore with an excellent appetite. The diet is based on special floating koi pellets; supplement with vegetables, greens, live and frozen food, and fruit. The amount depends on water temperature: metabolism slows in the cold, so feeding is reduced. They are prone to overeating.
Compatibility
Peaceful but very large fish. In a pond they mix with goldfish, Prussian carp, orfe, and other coldwater fish. They may accidentally swallow small fish. They usually dig up and graze pond plants. Keep in a group.
Breeding
Spawning is in spring and summer as the water warms above 18–20 °C. Koi scatter eggs over plants and spawning brushes, after which the parents are removed as they eat the eggs. Breeding true varieties requires careful fry selection: only a small fraction inherit a quality pattern.
Fun facts
Record koi live over 50 years; the famous fish Hanako is said to have reached 226. Dozens of classified varieties are recognised by colour and pattern. In Japan koi symbolise perseverance, luck, and family well-being.