Variations
14 kinds · tap one for a closer look
Koi
Friendly, can be hand-fed.
- Koi eats animals up to about 8 cm. Neon tetra only grows to 2.5 cm.
- Only a narrow pH range suits both: exactly 7.
- Koi eats animals up to about 8 cm. Cardinal tetra only grows to 3 cm.
- Koi needs cool water and makes a lot of waste, while Cardinal tetra is tropical.
- Koi eats animals up to about 8 cm. Black neon tetra only grows to 3.2 cm.
- Only a narrow pH range suits both: exactly 7.
- Only a narrow temperature range suits both: 24–25 °C.
77 species in our list are a good match.
Care and water
Behavior
Friendly, can be hand-fed.
Good to know: A pond fish. Even young koi outgrow almost every indoor aquarium.
Food
Koi pellets, vegetables.
Tap a food to see what it is.
Male or female
Males are slimmer with larger pectoral fins than females; females are fuller-bodied.
Health
Common problems. Tap one to see the signs. This is a guide, not a diagnosis.
Breeding
Egg-scatterer · Hard
Spawns in ponds in late spring and summer at about 18-25 °C, scattering sticky eggs onto plants or spawning ropes; males chase and nudge the female.
Choose healthy adults with good lines.
Large ponds.
Warming water in spring.
Very many eggs: about 100,000-120,000 per kg of female body weight. Common carp eggs hatch in about 4 days.
Infusoria, then powder food. Cull heavily.
- Poor genetics
- Not culling
- Overcrowding
Where it lives in the wild
Plants that suit it
The story of the koi
Koi are colour-selected Amur carp first bred for ornament in the Niigata area of Japan in the early 19th century (around the 1820s).
Koi were developed in Japan, especially around Niigata, where farmers raised carp as food in rice-growing villages and began selecting colourful mutants in the 1800s. Koi drew wide attention after being shown at an exhibition in Tokyo in 1914 and later spread around the world. The wild carp species they descend from was described by Lacépède in 1803.
First described by Bernard G. de Lacépède in 1803.
- Koi were first bred in the Niigata region of Japan.
- Koi can live for several decades.
- Show koi are judged on pattern, colour and body shape.
Sources
17 facts checked with sources
- Scientific name
Koi are a domesticated form, not a wild species. Eschmeyer's Catalog of Fishes and IUCN treat the Amur carp as Cyprinus rubrofuscus Lacepède, 1803 (Wikipedia, citing them). Many care sheets, vets and older books still call koi Cyprinus carpio (common carp), and genetic data suggest some koi also carry native Japanese carp ancestry (Wikipedia: 'believed to be artificially selected from both the Amur carp and the native Japanese carp'). A proposed name C. melanotus for the Japanese lineage has not been adopted. Keep 'Cyprinus carpio (koi)' as an other name.
Wikipedia: Koi (cites IUCN Red List, Eschmeyer's Catalog of Fishes) · FishBase: Cyprinus rubrofuscus summary - Familycorrected
Legacy has no family field. Subfamily Cyprininae.
FishBase: Cyprinus rubrofuscus summary - Size
Koi-specific sources: up to 75 cm (OATA, length type not stated, likely TL) and up to 3 ft / ~90 cm (PetMD). Legacy 70 cm sits within this. FishBase's 28 cm SL is for wild Amur carp, not domesticated koi, which are selected for large size.
OATA (Ornamental Aquatic Trade Association) pond fish leaflet, Sept 2022 · PetMD: Koi Fish Care Sheet (reviewed by Melissa Witherell, DVM) · FishBase: Cyprinus rubrofuscus summary - Temperature
OATA's 4-24 °C is its general range for pond fish including koi (not koi-only); legacy 25 is rounding. Ideal growing range is narrower: 15-25 °C (Wikipedia) or 64-75 °F = 18-24 °C (PetMD). Wikipedia notes immune systems are very weak below 10 °C.
OATA (Ornamental Aquatic Trade Association) pond fish leaflet, Sept 2022 · Wikipedia: Koi (cites IUCN Red List, Eschmeyer's Catalog of Fishes) · PetMD: Koi Fish Care Sheet (reviewed by Melissa Witherell, DVM) - pH
PetMD (koi-specific) 7.0-8.6; OATA general pond-fish range 6.5-8.5.
PetMD: Koi Fish Care Sheet (reviewed by Melissa Witherell, DVM) · OATA (Ornamental Aquatic Trade Association) pond fish leaflet, Sept 2022 - Hardnesscorrected
Legacy has no hardness. OATA figure is its general pond-fish range, which covers koi; not koi-specific.
OATA (Ornamental Aquatic Trade Association) pond fish leaflet, Sept 2022 - Smallest tankcorrected
OATA: pond of 4,500 L or more, preferably over 90 cm deep. PetMD: about 250 US gal (~946 L) per adult fish. Pond, not aquarium.
OATA (Ornamental Aquatic Trade Association) pond fish leaflet, Sept 2022 · PetMD: Koi Fish Care Sheet (reviewed by Melissa Witherell, DVM) - Group sizecorrected
PetMD recommends keeping at least five koi together. Only one source; treat as guidance.
PetMD: Koi Fish Care Sheet (reviewed by Melissa Witherell, DVM) - Lifespancorrected
Legacy 25-35+ is a fair typical figure but sources go higher: PetMD 'up to 50+ years'; FishBase gives max reported age 38 years for common carp. Claims of 100-226 years (the koi 'Hanako') are anecdotal (scale-ring count, 1974) and should not be used as typical.
PetMD: Koi Fish Care Sheet (reviewed by Melissa Witherell, DVM) · Wikipedia: Koi (cites IUCN Red List, Eschmeyer's Catalog of Fishes) · FishBase: Cyprinus carpio (common carp) summary - Temperament
OATA notes males can be rough with females during spawning.
PetMD: Koi Fish Care Sheet (reviewed by Melissa Witherell, DVM) - Swimming level
FishBase calls the wild species benthopelagic (bottom and mid-water); no source states 'all levels' in substance. Same treatment as goldfish.
FishBase: Cyprinus rubrofuscus summary - Care level
PetMD rates koi intermediate to advanced; they need a large, well-filtered pond.
PetMD: Koi Fish Care Sheet (reviewed by Melissa Witherell, DVM) · OATA (Ornamental Aquatic Trade Association) pond fish leaflet, Sept 2022 - Where it livescorrected
Legacy has no native range. Koi themselves are a domestic form with no wild range; most are bred in Japan, China, Israel and Southeast Asia.
FishBase: Cyprinus rubrofuscus summary · Wikipedia: Cyprinus rubrofuscus (Amur carp) · Wikipedia: Koi (cites IUCN Red List, Eschmeyer's Catalog of Fishes) - Male or female
Breeder source also gives vent shape: male concave, female convex. Breeding tubercles ('stars') on male pectorals/gill covers are standard for carp but were not found stated for koi in a fetched source.
Cuttlebrook Koi Farm (UK breeder): Ten Top Tips for Koi Breeding - Breeding
OATA warns spawning can injure females, especially with more males than females.
Cuttlebrook Koi Farm (UK breeder): Ten Top Tips for Koi Breeding · Wikipedia: Koi (cites IUCN Red List, Eschmeyer's Catalog of Fishes) · FishBase: Cyprinus carpio (common carp) summary - Eggs and youngcorrected
'Thousands' understates it: a large female lays hundreds of thousands. Hatch time: FishBase (common carp) says eggs hatch in 4 days, which fits the legacy 4-6 days (temperature-dependent); no koi-specific hatch time found.
Cuttlebrook Koi Farm (UK breeder): Ten Top Tips for Koi Breeding · FishBase: Cyprinus carpio (common carp) summary - Story
'Prize koi sell for huge sums' was not checked against a fetched source; left out of the value.
Wikipedia: Koi (cites IUCN Red List, Eschmeyer's Catalog of Fishes) · PetMD: Koi Fish Care Sheet (reviewed by Melissa Witherell, DVM)