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Color and pigment genetics

By the koi.wiki editorial team · Updated

Key facts: Koi coloration arises from pigment-containing skin cells called chromatophores, whose output is shaped by both genetics and diet; red and orange tones come mainly from carotenoid pigments obtained from food, while black comes from melanin produced within the fish[1][2].
The color of a koi’s skin results from specialized pigment cells called chromatophores, combined with structural coloration and the fish’s diet[1][3]. Chromatophores are classified by the color they produce: melanophores (black/brown), xanthophores (yellow), erythrophores (red/orange), iridophores and leucophores (reflective and white), and cyanophores (blue)[3][1].Unlike melanin, which fish synthesize internally, many red, orange and yellow pigments cannot be produced by the fish itself and must come from the diet[1]. This interplay between genetics and nutrition is why selectively bred ornamental koi such as those seen in Kohaku or Taisho Sanshoku require both the correct genetic pattern and appropriate feeding to display their full coloration[1][2].

Chromatophores and pigment cells

Chromatophores are pigment-containing cells found in the skin of ectothermic animals, including fish, and are grouped into subclasses by the color they display under white light: xanthophores (yellow), erythrophores (red), iridophores (reflective/iridescent), leucophores (white), melanophores (black/brown) and cyanophores (blue)[3]. At least six types of chromatophores have been described in fishes generally, with each cell type named for its principal pigment or the color it reflects[1]. The shape of the pigment-containing organelle within a chromatophore corresponds to the color produced[1].Melanophores contain eumelanin, an insoluble pigment formed through the breakdown of proteins and synthesized from tyrosine via the enzyme tyrosinase; eumelanin is packaged in vesicles called melanosomes distributed through the cell and is responsible for most dark browns, grays and blacks[3][1]. According to the US dealer Kodama Koi Farm, the black pigment melanin is produced by the koi itself rather than obtained from food, and functions in part as protective coloration: koi kept in darker environments may appear more jet-black, while those in brighter settings appear grayer, though this color-shifting applies to wild Magoi rather than improved nishikigoi varieties, whose black coloration is described as fixed[2]. The same source attributes the blue tones seen on some koi to melanin viewed through light-scattering skin layers, likened to the optical effect that makes deep water appear blue[2].

Carotenoids, diet and red/yellow pigmentation

Carotenoids are yellow, orange and red organic pigments produced by plants, algae and some microorganisms, not synthesized by the animals that display them; more than 1,100 carotenoids have been identified, divided into oxygen-containing xanthophylls and oxygen-free carotenes[5][1]. In fish, the carotenes astaxanthin and canthaxanthin are the most abundant carotenoid pigments and are responsible for predominant red pigmentation in many finfish and shellfish[1]. Astaxanthin is a keto-carotenoid, a metabolite of zeaxanthin and canthaxanthin, and is produced naturally by certain algae, yeast and bacteria before moving up the food chain to the animals that consume it[6].According to the US dealer Kodama Koi Farm, nishikigoi carry about three of the roughly twenty carotenoid pigments found in fish generally — lutein, zeaxanthin and astaxanthin — which are stored in skin pigment cells to produce red coloration, and which the koi cannot produce itself but must absorb from food[2]. Because of this dependence on diet, farmed koi raised without pigment supplementation lose vibrant hues and fade over time, and producers commonly add carotenoid sources to feed to ensure consistent, long-lasting coloration[1]. Fish differ in how efficiently they absorb particular carotenoids: salmonids absorb canthaxanthin and astaxanthin far more efficiently than lutein and zeaxanthin, whereas channel catfish show the opposite pattern, and the most desirable reds in ornamental fish are generally obtained from astaxanthin extracts[1]. Related pages discuss color-enhancing foods used to support this pigmentation.

Genetics versus environment in color expression

Skin color in fish is principally genetically determined, and can be inherited across generations, but several genes influence color rather than a single one, which allows environmental factors such as diet to strongly affect the final appearance and makes selective breeding for color slower and less predictable[1]. Wild color mutations in carp occur relatively commonly in nature, but according to one secondary source, such mutation-induced color change is distinct from the deliberate artificial selection used to create today’s ornamental koi varieties[4]. The same source notes that color inheritance in koi breeding is unstable, and that maintaining color variation through selection is costly; in current commercial koi farming, the proportion of superior-colored offspring relative to the total number of fry is reported to be less than 1%[4].Breeders use pattern terminology to describe how red (hi) and black (sumi) pigmentation is distributed, including classifications such as Maruten (a head spot separate from body markings) and Sandan (a three-step body pattern), according to the dealer Kodama Koi Farm[7]. Quality in major varieties such as Kohaku, Taisho Sanshoku and Showa Sanshoku is judged partly on the depth, edge sharpness (kiwa) and symmetry of these hi and sumi patterns, per the same source[7][8].

Research on how red and black are inherited

Peer-reviewed genetic studies specifically mapping the inheritance of red and black pigmentation in koi are not represented among the sources available for this article. What is documented is more general: skin color across fish species is described as polygenic, meaning multiple genes govern how much pigment such as melanin is produced and how it is deposited within chromatophores, which complicates straightforward Mendelian prediction of outcomes and slows selective breeding for color[1]. A secondary source states that color inheritance in koi is unstable and that selecting to maintain color variation is costly, citing a success rate of under 1% superior-colored fish among koi farm spawn as an illustration of this unpredictability[4].At the cellular level, research on chromatophores more broadly in fish and amphibians has established the biochemical pathways by which melanophores generate eumelanin from tyrosine via the enzyme tyrosinase, and how xanthophores and erythrophores derive their colors from pteridines and carotenoids respectively, sometimes within the same cell depending on the ratio of pigments present[3]. This general chromatophore biology underlies pigmentation in koi, even though koi-specific inheritance studies are not cited here[3][1].

Pigment patterns across varieties

Different nishikigoi varieties illustrate combinations of melanin- and carotenoid-based pigmentation. Utsurimono (写り物) varieties are black koi with white, red or yellow zebra-style markings; according to a secondary source, Shiro Utsuri, Hi Utsuri and Ki Utsuri are genetically the same as Showa Sanshoku but lack either red or white pigment[9]. Asagi display light blue coloration above the lateral line and red below, while Shusui, created by crossing Asagi with German mirror carp, shows a similar pale blue-gray and red/orange pattern on a largely scaleless body[10]. Koromo varieties combine a Kohaku-style red pattern with blue- or black-edged scales over the red areas[4].Solid metallic varieties grouped as Hikari-mujimono, including Ogon, display a single pigment type across the whole body combined with structural shine[4]. Goshiki combines a dark, reticulated base pattern with a Kohaku-style red overlay[11]. These pattern names describe how melanin- and carotenoid-based pigment cells are distributed rather than naming separate pigment chemistries[3][7].

Feeding practices and color maintenance

Because carotenoid pigments cannot be synthesized by the fish, farmers and keepers commonly supplement diets with pigment sources to enhance and maintain red and yellow coloration, and fish raised without such supplementation in aquariums or recirculating systems will lose vibrant hues over time[1]. According to Kodama Koi Farm, koi sold commercially are often fed color-enhancement (“color-up”) food specifically to bring out carotenoid-based pigments, and foods lacking these additives will not enhance coloration[2]. Further detail on these products is covered on the page about color-enhancing foods.

Common questions

Do koi produce their own red pigment?
No; according to the University of Florida IFAS Extension and the dealer Kodama Koi Farm, red and yellow carotenoid pigments such as astaxanthin, lutein and zeaxanthin cannot be synthesized by the fish and must be obtained from the diet[1][2].
Is black coloration in koi inherited or produced by the fish itself?
Black coloration comes from melanin, which koi produce internally rather than obtaining from food, unlike red and yellow carotenoid pigments[2][3].
Why is it hard to predict koi color outcomes from breeding?
Fish skin color is controlled by multiple genes rather than one, and environmental factors such as diet strongly affect final appearance, making selective breeding for color slower and less predictable; a secondary source notes that under 1% of farmed koi spawn achieve superior coloration[1][4].
What causes the blue color seen on some koi?
According to Kodama Koi Farm, blue coloration results from melanin pigment viewed through light-scattering skin layers, an optical effect compared to why deep water appears blue[2].
Has a specific gene for koi red/black patterning been identified in published research?
The sources used here do not describe a specific koi gene mapped by peer-reviewed study; available information is limited to general statements that color is polygenic and that inheritance of ornamental coloration is unstable[1][4].

References

  1. ^ UF/IFAS EDIS FA192: How Ornamental Fishes Get Their Color. University of Florida IFAS Extension (EDIS). ask.ifas.ufl.edu/publication/FA192. Retrieved November 2026.
  2. ^ What is a Nishikigoi? - Koi Fish History Explained and Meaning. Kodama Koi Farm (koi dealer). kodamakoifarm.com/what-is-nishikigoi-history-meaning/. Retrieved November 2026.
  3. ^ Chromatophore (Wikipedia). Wikipedia. en.wikipedia.org/wiki/Chromatophore. Retrieved November 2026.
  4. ^ Koi (Wikipedia). Wikipedia. en.wikipedia.org/wiki/Koi. Retrieved November 2026.
  5. ^ Carotenoid (Wikipedia). Wikipedia. en.wikipedia.org/wiki/Carotenoid. Retrieved November 2026.
  6. ^ Astaxanthin (Wikipedia). Wikipedia. en.wikipedia.org/wiki/Astaxanthin. Retrieved November 2026.
  7. ^ Koi Patterns and Markings: A Guide to Their Meaning, Types, and Selection. Kodama Koi Farm (koi dealer). kodamakoifarm.com/koi-patterns-and-markings/. Retrieved November 2026.
  8. ^ All About Gosanke Koi Fish Varieties "The Big Three!". Kodama Koi Farm (koi dealer). kodamakoifarm.com/gosanke-koi-fish/. Retrieved November 2026.
  9. ^ Koi (Wikipedia). Wikipedia. en.wikipedia.org/wiki/Utsurimono. Retrieved November 2026.
  10. ^ Koi (Wikipedia). Wikipedia. en.wikipedia.org/wiki/Shusui. Retrieved November 2026.
  11. ^ Koi (Wikipedia). Wikipedia. en.wikipedia.org/wiki/Goshiki. Retrieved November 2026.