What species are Koi Carp?
♪
Scales 29 lateral,
with markings unnatural;
that's Amur-ay ♪
Joshua Pickett
Adorned in sunset red daubs; peppered with dalmation-esque speckling; shiny, steel blue scales; streaked in vibrant orange; or completely piebald—these ornated fish come in a wild assortment of markings and colours that would've made the likes of even Vivienne Westwood envious. To the Japanese, they're called Nishikigoi, to species competition organisers, they're known as a nightmare, and to you and me, they're the kicky koi carp!
 |
| One of the oldest depictions of Koi Carp, illustrated around the time the "modern" strains were first being selectively bred. Utagawa Hiroshige, 1840-42. |
Koi weren't always like this, however, and no doubt most people know they are selectively bred "ornamental" fish, but what species are they exactly? For a long time, many of us have assumed they are just domesticated Common Carp (Cyprinus carpio), also known as the European Carp, as they are abundant in aquaculture for both fish-keeping and angling; why wouldn't it be them? As it happens, this is only part of the story, and it's more complicated than we might've expected. I won't bore you with the details... but the readers I might've would've buggered off by now, so, let's get into details!
Now, this is a tricky feature to write, and will no doubt trigger some debate and discussion; which, might I add, is completely welcome and justified. While the science is beginning to point towards an answer, it's not that clear cut yet, and there has been some simplification and omission here for the sake of effective communication, so let's take a deep breath before smashing abuse into your keyboard—hell hath no fury like that one, random social media 'expert' atop the first peak of Mount Dunning-Kruger.
Origins of Cyprinus in Eurasia
It all begins with the ancient mega-lake known as Paratethys (discussed before in a previous article); this vast, inland sea was Eurasia's greatest biodiversity hotspot, and countless freshwater species we see across the continent were descended from the species inhabiting Paratethys itself. The lake, which peaked in size approximately 10 million years ago (becoming the largest lake in our planet's history), went through a great deal of change that led to its eventual draining in the Pliocene, leaving behind three smaller inland seas (Aral, Black and Caspian). It appears that the carp which were ancestral to Cyprinus carpio evolved in the Caspian Sea during the end of the Pliocene (5.3–2.6ma). With the numerous glacial periods during the Pleistocene (2.5ma–11,700ya), different pathways were closed and opened for them, forcing their range to branch radically. It pushed them West into the Black Sea basin (even into the Danube River post glacier); and East into the Aral Sea basin, pushing into the far East of mainland Asia. One branch of carp whose populations trended mostly westerly, stemmed into the well-known European/Common Carp (Cyprinus carpio); and those which made their way far East, stemmed into the Amur Carp (Cyprinus rubrofuscus).
 |
The carp which migrated outwards from the Caspian Sea, with a westerly trend, became the European/Common Carp Cyprinus carpio (native range¹, as of 2022, in orange). |
When this became known to us, scientists at the time had tentatively recognised both the western (European) and eastern (Asian) branches to just be Cyprinus carpio. Later, the eastern branch was defined by two distinct populations, the southern group, "viridi-violaceus" and the northern group haematopterus, though the differences between the longitudinal groups was of no significance in comparison to the differences between their counterparts in Europe. The Asian branch was redescribed as Cyprinus carpio haematopterus, a subspecies of Cyprinus carpio, though contemporary research has gone a step further, and shown meristic and genetic evidence which positions the Asian branch as a species of their own, Cyprinus rubrofuscus, the East Asian Carp, better known as the Amur Carp.
Historic Cultivation
For roughly 2,400 years, humans have been cultivating carp for food. The first of whom were evidenced to do so were the Romans, who had collected specimens of Common Carp from the Danube River (their most westerly range at the time). They had reared them in ponds, called "piscinae" which persisted as tradition in monasteries throughout the Middle Ages. It appears Common Carp ranging further West than the Danube was entirely down to human interference; though the history and motivation for bringing carp to western Europe, while a far more well-known story which has been told in other literature, is extraneous to the origin of koi.
Around the same time as the Romans, possibly earlier, carp were also being bred for food across Asia (China, Korea and eventually Japan). There's little evidence to tell us what species these were exactly, though it's more-than-likely they were the native Cyprinus species, such as the Amur Carp, and perhaps a medley of other local species too, such as Black, Bighead, Grass, and Silver Carp.
 |
| Black Carp Mylopharyngodon piceus are fast growing and able to exceed 200lb; it's no wonder these freshwater megafauna are among the world's 15 most cultured food fishes. © Jo Kuyken / Animal Taxonomy Database |
When
Amur Carp were introduced to Japan, roughly 1,000 years ago, farmers reared
them in mud ponds to supplement their diet. During their spawning in captivity,
farmers would've noticed the odd carp differing in appearance to the rest of
the fry. These are colour morphs and are completely normal for all animals;
with morphs including albinism (albino), erythrism (red), xanthism
(yellow/orange), melanism (black), and leucism (a group of morphs lacking in
pigment). In the wild, animals with these morphs stick out like a sore thumb,
and tend to be eaten before reaching maturity, but in captivity their survival
rate jumps. Cultures which bred carp would've seen such morphs (we still do today²), but it seems back then, it
was the Japanese who were more infatuated with them, keeping them as prized
pets, whereas the Romans still used them as food regardless of morph. In the
early 19th century (1840–1844), this was celebrated further with the Japanese
Niigata Prefecture artificially selecting these morphs, presumably beginning
with the so-called Red Carp, which were already revered at the time, and known
to us today as a xanthic morph of Amur Carp which take on an orangish hue.
This supposed "mother-of-all-koi" was named Hookazuki, and there have been varying accounts on its existence, though still far more credible than the claims made about Hanako, an alleged 226-year-old Scarlet koi born in 1751 and died in 1977. Very few people have also brought up the fact that Hanako would've also pre-dated the Japanese koi strain of which she was descended from in the first place. In any case, her final owner was very guarded when it came to allowing people to independently verify the claim, with the owner alleging they had inspected two of Hanako's scales (a flawed way to determine age, if true).
Quickly after the emergence of Hookazuki, selective breeding of different morphs, generated unique markings which allowed these carp to become the ornamental Nishikigoi, "Swimming Flowers", or Koi Carp that we know and love today.
 |
| These
fish (up to 30") were selected in person during a visit to a Japanese
koi farm and exported back to the retailer in the UK. One of the
qualities they look for are crisp edges around the markings in the adult fish;
a feature normally seen in juveniles, but fades in lower grade koi as
they grow. Some of the individuals that were in this pond fetched for over £3,000. © Cuddra Aquatics |
"Although the diversity of the East Asian species of Cyprinus has long been documented in the Chinese literature, it is largely ignored, if not flatly negated, in western literature, where it is often assumed that Asian carps are derived from introduced European carps and that the species recognized by Chinese authors are domesticated or feral forms." —Kottelat, M. (2006)
Presently, it seems that Koi Carp are accepted as being domesticated Amur
Carp (Cyprinus rubrofuscus), and are
not descended from Common Carp (Cyprinus
carpio); despite the initial delay in western literature to acknowledge this.
Well, just to throw some fuel on the fire, it seems that Common Carp made their way to Japan shortly after they were first selectively breeding Amur into koi, along with other Cyprinus species too! The consequences of this, means that the koi we know may have a mixed heritage. Other breeders could've bred ornamental carp from other closely related Cyprinus species, some may have unknowingly crossed multiple species. Breeders could've also traded different strains increasing the gene pool and preventing complications from inbreeding, though largely all the koi which come out of Japan are mostly C. rubrofuscus in origin. Additionally, the long delay in recognising the different species meant that Common Carp may have been introduced to koi bloodlines in Europe, potentially mixing a further time.
 |
| Koi in mixed species fisheries will occasionally hybridise with other carp, though you'd probably never be able to tell visually. |
How do you identify them?
Modern angling has complicated this even more, as fisheries which have multiple cyprinid species in the same lake, will result in hybrids, and yes, they are fertile! Though fisheries which do stock ornamentals like koi, do not [usually] like to dilute their bloodlines with the typical Common/Mirror carp, so it's safe to say, if you catch a koi, it should still be considered an Amur Carp, according to the available science; at least as close as you can get without catching the wild type. Though the only [known] exception would be the Ghost Carp, which begins as a traditional 50/50 hybrid of one of two koi strains with Common/Mirror carp.³
 |
| Wild Amur Carp Cyprinus rubrofuscus from the Amur River © Food and Agriculture Organization of the United Nations |
 |
| True wild (Sazan) Common Carp Cyprinus carpio from the Danube River © Fennel's Journal, No. 4 Wild Carp (2020) |
If you really want to be certain (as best you can) that the koi you're trying to identify is an Amur Carp, you can check their lateral line scales. Common Carp have 33–37, whereas Amur Carp average less with just 29–33. Though, there's sometimes fluctuation outside of these meristic averages, especially with cultivated fishes, so it's not a sure thing, though it is the best method after genetic testing.
 |
| On vibrant koi such as this, you can see the lateral line clearly dotted horizontally along the scales; it is the scales along this row which you should count. |
For the purists out there, don't be alarmed that there may be more than one species mixed into their distant heritage, this is common for over 10% of all animal species, especially birds and freshwater fishes. Modern humans from Europe and Asia, for example, can share no more than 3% DNA with Homo neanderthalensis and remarkably up to 5% with the (to-be-categorised) Denisovans. Similarly, a different species may be introduced into the bloodline of another species through very occasional hybridisation, but as the generations pass by, the introduced species is, for lack of a better word, "diluted" to an imperceptible amount. This happens naturally all the time (arguably more than we've been able to observe), or through anthropogenic means, like escapees or misidentifications in aquaculture. On the other end of the spectrum, you have hybrid speciation, where a new species can arise if it's beneficial for two different species to hybridise (occurring mostly in plants and insects, but some vertebrates too, perhaps most notably the Clymene Dolphin Stenella clymene).
Remember, this is not all cut and dry, as what defines a species is completely arbitrary; after all, there's no exact boundary between the end of one species and the start of another—it's just the best way we have to organise taxa. There are also major inconsistencies surrounding what to categorise domesticated animals as, since there's no universally accepted system in place, as of yet.
● Some are considered distinct species, such as the Domestic Cat Felis catus, which are the domesticated North African Wildcat Felis lybica.
● Others are regarded as subspecies, like the Ferret Mustela putorius furo, a domestication of the European Polecat Mustela putorius.
● Lastly, there are those who are considered forms of the same species, with no recognised change in nomenclature, such as the Silver Fox Vulpes vulpes, sharing the same scientific name as its wild counterpart, the Red Fox.
 |
| The goldfish Carassius auratus is another example of a domesticated species sharing the same scientific name as its ancestral species. No, they're not descended from the Prussian Carp Carassius gibelio, as some literature cites, although they do also take on 'gold' forms. Pictured is one of the many "Fancy" goldfish breeds, a juvenile Oranda, bred for the aquarium trade. |
Again, the way these have been categorised comes down to largely (though not exclusively) which side of the argument the authors rest on. It is the latter of which the Koi Carp falls into; not considered its own species, nor a subspecies of the Amur Carp, but it is currently recognised as an ornamental form of the Amur Carp. There's strong arguments on all sides, which I'll link here, (summarised by communicator and paleo-artist, Daniel Foidl quite well). I'll add, neither side is wrong, they are just in pursuit of a clearer and consistent system for the scientific categorisation of domesticated animals, so it's within reason that this decorated descendant of the Amur Carp could one day be categorised as a subspecies of them, or perhaps even its own species entirely.
 |
| There is some debate as to whether ornamentals such as koi should be allowed in recreational fisheries, due to the evidence that their domestication has fundamentally changed their behaviour in how they interact with humans. |
_______
¹ The true wild European/Common Carp Cyprinus carpio (Sazan), of which the cultivated so-called "King Carp" descend are virtually extinct, limited only to isolated shoals in rivers draining into the Black and Caspian seas—many of which have been accidentally cross-bred out of existence with the cultivated strains, thanks to flooding events which connected the cultivation farms with the rivers. The majority of wild Common Carp you see in this native range map, are now replaced by feral King Carp (wildies).
² It is possible to create your own ornamental carp with any species of Cyprinus, as the colour morphs which led to Amur Carp becoming koi, are not exclusive to them. A great example of this is carp breeder Ross Osborne, who has occasionally encountered xanthism in some of his stock of "Mirror" strain Common (King) Carp, which give them an orange colour. Ross calls them "wild koi" (as he did not selectively breed for them), and whilst they're not true koi (as these are not ornamental domesticated Amur Carp), they are a near perfect modern example (sans the "mirror" scales) of what early 19th century Japanese breeders would've seen (xanthic carp, which they aptly named "Red Carp"), cultivating them for more ornamental colours and markings.
³ True Ghost carp are a cross of European/Common Carp Cyprinus carpio (either Common or
Mirror) and either of the following two breeds of ornamental Amur Carp Cyprinus rubrofuscus: Yellow Ogon
(Yamabuki) to make Yellow Ghost Carp; or Platinum Ogon (Purachina) for White
Ghost Carp.
_______
Appendix 1 the Propagation Technologies for Chinese major carps (1982) MADAGASCAR TECHNICAL ASSISTANCE FOR INLAND FISHCULTURE AND FISHERY IMPROVEMENT (Third Consultancy). Available at: https://www.fao.org/4/p8669e/P8669E03.htm (Accessed: 07 December 2024).
Balon, E.K. (1995) ‘Origin and domestication of the wild carp, Cyprinus carpio: From roman gourmets to the swimming flowers’, Aquaculture, 129(1–4), pp. 3–48. doi:10.1016/0044-8486(94)00227-f.
Craig, J.F. (2015). Freshwater Fisheries Ecology. Wiley-Blackwell. p. 297. ISBN 978-1-118-39442-7.
Dyldin, Yu.V. et al. (2023) ‘Ichthyofauna of the fresh and brackish waters of Russia and adjacent areas: Annotated list with taxonomic comments. 2. Order Cypriniformes, Suborders Catostomoidei, Cobitoidei and Cyprinoidei’, Вопросы ихтиологии, 63(4), p. 386. doi:10.31857/s0042875223040069.
Fife-Cook, I. and Franks, B. (2021) ‘Koi (Cyprinus rubrofuscus) seek out tactile interaction with humans: General patterns and individual differences’, Animals, 11(3), p. 706. doi:10.3390/ani11030706.
‘Fishes of the Indochinese Mekong’ (2021) in. Nagao Natural Environment Foundation, p. 153. [Directly linked as this is a great and free resource]
Gentry, A., Clutton-Brock, J. and Groves, C.P. (2004) ‘The naming of wild animal species and their domestic derivatives’, Journal of Archaeological Science, 31(5), pp. 645–651. doi:10.1016/j.jas.2003.10.006.
Kottelat, M. (1997). European freshwater fishes. An heuristic checklist of the freshwater fishes of Europe (exclusive of former USSR), with an introduction for non-systematists and comments on nomenclature and conservation. Biologia, Bratislava, Section Zoology, 52 (Suppl.5): 1–271.
Kottelat, M. (2001a). Fishes of Laos. Wildlife Heritage Trust Publications, Colombo.
Kottelat, M. (2006) Fishes of Mongolia: A check-list of the fishes known to occur in Mongolia with comments on Systematics and nomenclature. Washington, D.C: Environment and Social Development Unit, East Asia and Pacific Region, World Bank. [Directly linked as this is a great and free resource]
Kottelat,
M. (2001b). Freshwater fishes of northern Vietnam. A preliminary
check-list of the fishes known or expected to occur in northern Vietnam
with comments on systematics and nomenclature. World Bank, Washington.
Liu, Z. et al. (2020) ‘Differentiating wild, Lake-farmed and pond-farmed carp using stable isotope and multi-element analysis of fish scales with chemometrics’, Food Chemistry, 328, p. 127115. doi:10.1016/j.foodchem.2020.127115.
Macholán, M. (2013) ‘Hybridization, organismal’, Brenner’s Encyclopedia of Genetics, pp. 594–597. doi:10.1016/b978-0-12-374984-0.00759-2.
Mousavi-Sabet, H. et al. (2023). Exotic fishes in the southern Caspian Sea basin; with four new records. Iranian Journal of Ichthyology, 10(1), 28–40. https://doi.org/10.22034/iji.v10i1.978.
Species that contain: Cyprinus and rubrofuscus (2024) Eschmeyer’s Catalog of Fishes. Available at: https://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp
U.S. Fish & Wildlife Service (2019) Cyprinus rubrofuscus ecological risk screening summary. Available at: https://www.fws.gov/sites/default/files/documents/Ecological-Risk-Screening-Summary-Koi.pdf (Accessed: 07 December 2024).
Wang, M. et al. (2024) ‘Asymmetric and parallel subgenome selection co-shape common carp domestication’, BMC Biology, 22(1). doi:10.1186/s12915-023-01806-9.
Wang, S.-Y. et al. (2013) ‘Origin of Chinese goldfish and sequential loss of genetic diversity accompanies new breeds’, PLoS ONE, 8(3). doi:10.1371/journal.pone.0059571.
Wu, H.-W. et al. (1977). The cyprinid fishes of China. 2. Technical Printing House, Shanghai, 2: pp. 229–598, 109 pls. [Translated from Chinese].
Yue, P.-Q. et al. (2000). Fauna Sinica. Osteichthyes. Cypriniformes III. Science Press, Beijing, v+653 pp.
Zhou, J. et al. (2004). Molecular phylogeny of three subspecies of common carp Cyprinus carpio, based on sequence analysis of cytochrome b and control region of mtDNA. Journal of Zoological Systematics and Evolutionary Research, 42: 266–269.
