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Taxonomy: Cyprinus rubrofuscus or Cyprinus carpio?

By the koi.wiki editorial team · Updated

Key facts: Koi were long described as a domesticated form of the common carp, Cyprinus carpio, but most recent genetic authorities instead treat them as a domesticated Amur carp, Cyprinus rubrofuscus, a separate East Asian species[1][2].
The scientific name applied to koi (錦鯉, nishikigoi) has shifted as genetic analysis has advanced. Older literature almost universally calls koi a variety of Cyprinus carpio, the common carp of Europe and western Asia[3][1]. More recent molecular studies of mitochondrial DNA, microsatellite DNA, and genomic DNA have found a clear genetic split between the European/West Asian carp population and an East Asian population that includes koi, leading many authorities to reclassify the East Asian lineage as its own species, Cyprinus rubrofuscus, commonly called the Amur carp[1][2].Because of this ongoing reclassification, both names remain in circulation. Some literature still uses C. carpio or C. carpio haematopterus for koi, while newer sources use C. rubrofuscus (with C. c. haematopterus treated as a junior synonym)[6][2]. Regardless of which Latin name is used, sources agree koi are a domesticated, selectively bred population rather than a distinct wild species of their own[1].

The two candidate species

Cyprinus carpio, the common carp, is native to Europe and western Asia, with wild populations centered on basins draining to the Black, Caspian, and Aral seas; the type subspecies is C. c. carpio[4][3]. Cyprinus rubrofuscus, the Amur carp, originates in eastern Asia, with a native range spanning Mongolia, Russia, China, Laos, and Vietnam, and was historically treated as the eastern Asian subspecies C. c. haematopterus[2][6].The two can be distinguished by meristic counts: Amur carp have fewer lateral line scales (29–33) than common carp (33–37), but more branched dorsal rays (18–22 versus 17–20)[2][4]. Wild common carp tend toward gray and bronze coloration, while wild Amur carp are typically silver-bodied with red pelvic, anal, and caudal fins, though some Laotian stocks are solid gray[2][7].

The genetic case for C. rubrofuscus

Several studies using mitochondrial DNA, microsatellite DNA, and genomic DNA have found a clear separation between European/West Asian carp populations and East Asian populations, with koi falling into the East Asian group[1]. On the basis of this split, recent authorities — including ITIS and the IUCN Red List — have recognized the Amur carp as a distinct species, C. rubrofuscus, rather than a subspecies of C. carpio[2][6]. One mitochondrial DNA study was unable to find clear geographic structure, possibly because of historical translocation of carp stocks between regions, illustrating that extensive hybridization and movement of populations has complicated the historical zoogeography of carp relatives[1].Even among studies supporting a separate East Asian species, questions remain. One mtDNA study suggested koi are genetically closer to Southeast Asian carp populations than to Chinese stocks, and researchers have noted that a fuller taxonomic review of Cyprinus carp from eastern and southeastern Asia may be needed because genetic variation does not neatly match currently recognized species boundaries[1]. Separately, some researchers have proposed that Japan's native carp lineage is a distinct species, tentatively identified as Cyprinus melanotus, based on nineteenth-century descriptions by Philipp Franz von Siebold and on more recent mitochondrial DNA analysis distinguishing native Japanese carp from carp introduced from Eurasia; a new scientific name for this native lineage is reportedly under consideration[1].

Why C. carpio persists in the literature

Because C. rubrofuscus was for many years treated as a subspecies of the common carp under the name C. carpio haematopterus, a large body of older and some current literature continues to refer to koi as C. carpio or C. carpio carpio[2][6]. In scientific literature more broadly, the Amur carp is still often listed under the synonym C. carpio haematopterus[2]. A molecular study of the Amur carp mitogenome similarly classified the fish as a subspecies in its tree construction, even though the species has since gained standing as its own species in subsequent taxonomic treatments[2].The Wikipedia entry for the common carp itself notes that C. c. haematopterus was recognized in the past but that recent authorities treat it as the separate species C. rubrofuscus, and that koi (錦鯉, nishikigoi in Japanese; 鯉魚 in Chinese) is a domesticated ornamental variety whose parent species is likely the East Asian carp, possibly C. rubrofuscus[3].

Domestication, not a new species

Regardless of which Latin binomial is used for the ancestral wild population, sources agree that koi themselves are not a separate species from their wild ancestor. Koi are described as domesticated Amur carp that have been selected or culled for color, and if allowed to breed freely they will revert to the original wild coloration within a few generations[1]. Carp have been cultured in Japan for over two thousand years, and genetic data suggest nishikigoi were artificially selected from both Amur carp stock and native Japanese carp[2].Most ornamental koi varieties distributed worldwide today are described as originating from Amur carp bred in Japan during the first half of the nineteenth century[1]. A separate account dates the domestication of koi carp as an ornamental variety to the Niigata region of Japan in the 1820s, again noting its parent species is likely the East Asian carp, possibly C. rubrofuscus[3].

A Japanese industry definition of nishikigoi

Separate from the biological species debate, Japan's agricultural standard JAS 0020, issued by the Ministry of Agriculture, Forestry and Fisheries, defines nishikigoi administratively as carp (Cyprinus carpio) possessing ornamental external characteristics, and explicitly uses the scientific name Cyprinus carpio in its definition[5]. The same standard defines a nishikigoi “variety” (品種) as a type classified by shared external characteristics such as body shape, color, and pattern, and includes a footnote clarifying that this commercial sense of “variety” differs from the biological taxonomic rank of species (種)[5]. This illustrates how a regulatory or industry definition can continue to use C. carpio even as biological taxonomy moves toward C. rubrofuscus[5][2].Confusion between carp lineages extends to several commercially recognized hybrids. Ghost koi are described as an artificial hybrid bred between common carp and Japanese “Purachina” koi, valued commercially for the wide range of colors the cross produces[3]. Mirror carp, also called Israeli carp, are a scaled variant of the common carp produced through selective breeding for large, mirror-like scales caused by a recessive genotype at specific scale-trait loci, and are a separate lineage from ornamental koi[3].Goldfish (Carassius auratus), which were developed in China more than a thousand years ago and can superficially resemble koi, especially the butterfly koi and plain-colored forms, belong to an entirely different genus; koi and goldfish can interbreed, but because they come from different species of carp, their offspring are sterile[1].

Common questions

Is koi's scientific name Cyprinus carpio or Cyprinus rubrofuscus?
Both names appear in the literature. Older and some current sources use Cyprinus carpio[3][5], while recent genetic studies favor Cyprinus rubrofuscus (Amur carp) as the ancestral species, since East Asian and European/West Asian carp populations form genetically distinct groups[1][2].
What is the Amur carp?
The Amur carp (Cyprinus rubrofuscus) is an East Asian freshwater fish native to Mongolia, Russia, China, Laos, and Vietnam, and is considered the ancestral form of some domesticated koi[2].
Are koi a different species from common carp?
Koi are not considered a separate species from their wild ancestor; they are a domesticated, selectively bred population that will revert to wild coloration within a few generations if left to breed freely[1].
Can koi and goldfish interbreed?
Koi and goldfish can interbreed, but because they descend from different species of carp, their offspring are sterile[1].
Does Japan's own standard use a scientific name for nishikigoi?
Yes. Japan's JAS 0020 standard defines nishikigoi as carp (Cyprinus carpio) with ornamental external characteristics, and separately defines “variety” as a commercial classification distinct from biological species[5].

References

  1. ^ Koi (Wikipedia). Wikipedia. en.wikipedia.org/wiki/Koi. Retrieved November 2026.
  2. ^ Cyprinus rubrofuscus (Wikipedia). Wikipedia. en.wikipedia.org/wiki/Amur_carp. Retrieved November 2026.
  3. ^ Common carp (Wikipedia). Wikipedia. en.wikipedia.org/wiki/Common_carp. Retrieved November 2026.
  4. ^ Cyprinus carpio, Common carp : fisheries, aquaculture, gamefish, aquarium. FishBase. fishbase.se/summary/Cyprinus-carpio.html. Retrieved November 2026.
  5. ^ JAS 0020 Nishikigoi. Vocabulary (MAFF) — Ministry of Agriculture, Forestry and Fisheries (Japan). maff.go.jp/j/jas/jas_standard/attach/pdf/index-536.pdf. Retrieved November 2026.
  6. ^ Cyprinus rubrofuscus (Wikipedia). Wikipedia. en.wikipedia.org/wiki/Cyprinus_rubrofuscus. Retrieved November 2026.
  7. ^ Cyprinus rubrofuscus. FishBase. fishbase.se/summary/Cyprinus-rubrofuscus.html. Retrieved November 2026.