fish · Cyprinidae

Koi

Cyprinus carpio

Wild range: Domesticated ornamental form (nishikigoi) developed in Niigata, Japan; no wild 'koi' population. Wild Cyprinus carpio native to Black/Caspian/Aral basins (Europe–western Asia); East Asian Amur carp Cyprinus rubrofuscus (China/Mongolia/Russia) frequently cited as ornamental-koi ancestor (Asia)

At a glance: Koi care

Compiled reference information. Review the care notes and original sources below.

What temperature is listed for Koi?

The compiled profile lists 4.0–28.0 °C for Koi (Cyprinus carpio). Check the original sources below for context and differing recommendations.

What tank size is listed for Koi?

The profile lists a minimum tank volume of 1000.0 US gallons (3785.0 liters). Volume alone does not establish suitability; consider dimensions, group size and other inhabitants alongside the full care notes.

What pH is listed for Koi?

The compiled profile lists a pH of 6.5–8.5. Review the cited care sources alongside the other water parameters in this profile.

Natural habitat

Large, long-lived ornamental carp kept as outdoor pond fish. Extreme bioload; adults routinely 60–90 cm. Indoor aquariums are unsuitable for long-term adult housing — juveniles outgrow tanks within the first year. Need deep, heavily filtered ponds with open swimming space.

Where they are found

Catalog primary locked as Cyprinus carpio Linnaeus, 1758 per inventory/trade lock and ITIS Current Standing valid (TSN 163344). Eschmeyer Catalog of Fishes Current status Valid as Cyprinus carpio Linnaeus 1758 (spid 3028; CoF notes widely introduced multicolor varieties). Separate CoF/FishBase/IUCN species Cyprinus rubrofuscus Lacepède 1803 (Amur / East Asian carp; CoF spid 28823 Valid; FishBase summary; IUCN LC) is treated by many modern aquarium sources (Guidarium, AquariumStocking, Wikipedia Cyprinus rubrofuscus) as the ancestral lineage of ornamental koi — recorded in aliases and here, not adopted as primary (Scott naming rule 2026-09-24). Trade names: koi, nishikigoi, Japanese carp. Ornamental varieties (Kohaku, Sanke, Showa, Ogon, butterfly/longfin, etc.) are selectively bred forms, not separate species.

Aquarium care

Pond fish — not a home-aquarium species. Locked minimum ~1000 US gallons (~3785 L) for a small group (Guidarium 3785 L / ≥300 cm length; AquariumStocking 1000 gal min / 2000 gal recommended; PetMD ~250 gal per adult individual and 1000+ gal for a small school). Depth ≥3 ft for temperature stability and winter survival under ice. Heavy multi-stage pond filtration and aeration required (extreme waste). Soft-to-hard alkaline water ~4–28°C, pH ~6.5–8.5, GH ~8–15 dGH (Guidarium 4–28°C / pH 6.5–8.5 / 4–15 dGH; AquariumStocking 4–28°C / pH 7.0–8.5 / 8–25 dGH; PetMD preferred active band ~18–24°C / pH 7.0–8.6; FishBase C. carpio absolute 3–35°C / pH 6.5–9.0 / dH 10–15 — locked core overlap 4–28°C, 6.5–8.5, 8–15 with PetMD preferred 18–24°C, Guidarium GH lower to 4, AquariumStocking GH upper to 25, and FishBase absolute extremes noted). Stop or sharply reduce feeding below ~10°C. Intermediate difficulty: predator protection, quarantine (KHV risk), and oversized filtration are non-negotiable.

Feeding

Omnivore — quality koi pellets as staple plus seasonal wheat-germ formulas in cooler water; color-enhancing and growth formulas in warm months (PetMD, AquariumStocking). Offer only what is eaten in a few minutes; remove leftovers. Fresh vegetable treats OK; avoid bread/fillers. Do not feed in near-freezing water (digestion stalls).

Compatibility

Peaceful, social pond fish — keep at least 3 (Guidarium); PetMD prefers ~5+. Compatible with large goldfish and other cold-tolerant pond cyprinids in adequately sized ponds. Will eat small fish/fry and uproot most plants. Not community aquarium fish. Quarantine all new arrivals 4–6 weeks (Koi herpesvirus / KHV).

Breeding

Outdoor ponds spawn naturally in spring when temperatures climb past ~18–20°C; males chase females; sticky eggs on plants hatch in days (FishBase / AquariumStocking). Controlled breeding and culling are how quality nishikigoi are produced — casual pond spawns rarely yield show-grade fish. Remove adults or eggs if uncontrolled fry are unwanted.

Sources

Compiled from multiple independent care sheets — not copied from a single site.