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Koi breeding

By the koi.wiki editorial team · Updated

Key facts: Koi breeding is the deliberate spawning and selective rearing of nishikigoi (錦鯉), in which breeders pair chosen parent fish (oyagoi, 親魚), hatch large numbers of eggs, and cull the great majority of fry to isolate the rare individuals with desirable color and pattern[1][2].
Koi breeding originated in the Nijūmuragō (二十村郷) area spanning Ojiya and Yamakoshi in Niigata Prefecture, where farmers raising common carp for food in terraced paddy ponds began, during the Bunka and Bunsei eras (1804–1830), crossing red, white and black individuals to fix red-and-white coloration[1][2]. From this base population nearly all later nishikigoi varieties were developed, with the exception of the metallic Ogon varieties, which emerged more recently[1].Modern breeding still follows the same basic biological process as the carp's wild ancestors: a female releases a large number of adhesive eggs which a male fertilizes, usually in spring and summer[1][4]. Because even champion-grade parents produce mostly offspring that are not acceptable as nishikigoi, breeders rely on intensive culling (選別, senbetsu) at multiple stages to isolate the rare fry worth keeping[1][2]. According to the Japanese-language Wikipedia article on nishikigoi, the proportion of superior individuals from a single spawning is typically below 1 percent[2].

The breeding process

Koi reproduce through broadcast spawning: the male follows and nudges the female, she releases eggs that sink and stick to surfaces such as spawning ropes or mats, and one or more males fertilize them externally[1][3]. According to a US koi dealer, hobbyist spawning setups commonly use one female with two to three males, all older than three years, placed in a tank with spawning ropes once water temperature reaches around 75°F (24°C)[3]. The Southern Regional Aquaculture Center notes that koi and goldfish generally spawn as water temperature approaches 68°F (20°C), that spawning most often occurs in early morning, and that both species eat their own eggs, so broodstock must be separated from egg-covered mats quickly[4].Eggs hatch within a few days depending on temperature; the Kodama Koi Farm describes hatching in about 3 days at a steady 77°F (25°C), while the Southern Regional Aquaculture Center reports hatching in 46 to 54 hours at 84°F (29°C) or 5 to 7 days at 70–75°F (21–24°C)[3][4]. Fry require food roughly 24 hours after hatching; hobbyist guidance describes feeding newly hatched fry brine shrimp (Artemia) before transitioning to artificial feed after about 10 days, while professional breeders in Japan more commonly culture water fleas as a first food[3].

Sexing and selecting oyagoi (parent koi)

Choosing broodstock, or oyagoi (親魚), requires distinguishing males from females. According to the US dealer Kodama Koi Farm, females tend to be rounder and fuller-bodied, especially when carrying eggs, and grow larger in length and girth, while males are slimmer and more torpedo-shaped with larger, stiffer pectoral fins[5]. During the breeding season, males may develop small white breeding tubercles on their gill covers and fins and will actively chase females, whereas females appear swollen in the abdomen and move more slowly[5].The Southern Regional Aquaculture Center notes that brood fish should be selected for traits such as size, color, health and finnage, and that the quality of offspring is directly related to the quality of the broodstock[4]. It adds that champion koi broodstock command very high prices and are usually accompanied by a pedigree demonstrating purity of bloodline, whereas inexpensive, common koi may cost less to breed than the value of the resulting offspring[4]. For background on general animal breeding concepts such as purebred lines and selection for stable traits, see the broader subject of selective breeding[6].

Culling (senbetsu)

Because a single spawning can produce thousands of offspring, and the large majority are unsuitable as ornamental nishikigoi or may carry genetic defects, breeders cull fry at successive stages based on experience and closely guarded techniques[1]. The Japanese-language Wikipedia article on nishikigoi states that the share of superior individuals from a typical spawning is under 1 percent[2]. Culled fry are commonly destroyed or used as feeder fish, while older culls sold in their first year, typically 3 to 6 inches (7.6–15 cm) long, are referred to as tosai and sold as lower-grade, pond-quality koi[1].The Southern Regional Aquaculture Center describes culling and grading as both mechanical, using grader boxes for size, and manual for appearance, noting that this labor is a significant production cost and that expertise in grading ornamental fish takes time to develop[4]. A US koi dealer notes that some fry colors, such as black individuals, can be sorted out using purpose-built separation equipment, and recommends beginners start with varieties that are comparatively easy to sort, such as Shiro Utsuri, or with Kohaku if more red coloration is desired in the resulting pond[3].

Niigata and mud ponds

Niigata Prefecture remains closely associated with koi breeding history and practice. The Nijūmuragō area, covering parts of present-day Ojiya and the Yamakoshi area of Nagaoka, is described as the birthplace of nishikigoi, where farmers raising carp in terraced rice-paddy ponds selected and crossed red, white and black individuals over generations[2][1]. For more on this origin area and its history, see Nijumurago: Ojiya and Yamakoshi, Niigata and the 2004 Chuetsu earthquake and the koi industry, which according to the Japanese-language Wikipedia article caused devastating damage to koi farms in the former Yamakoshi village[2].A breeder profiled by the US dealer Kodama Koi Farm, Seiki Igarashi, operates a farm in the mountains near Ojiya city and breeds Gosanke varieties including Kohaku, Sanke and Showa; according to the same source, the number of breeders in Niigata fell from about 6,000 when he began breeding in 1966 to around 200 decades later[7]. This decline is attributed in the source to the highly competitive, artwork-like nature of nishikigoi breeding, where only superior fish find buyers[7].

Variety outcomes of breeding

Selective crossing over nearly two centuries produced the range of patterns and colors recognized today. The Japanese-language Wikipedia article on nishikigoi lists principal body colors including white, black, red, blue, green, yellow, purple and cream, along with metallic gold- and silver-scaled forms, and states that nishikigoi are said to number around 130 varieties, with the best-known category being the Gosanke group of Kohaku, Taisho Sanshoku and Showa Sanshoku[2]. English-language Wikipedia likewise identifies Gosanke as the most popular category[1].Scaleless varieties, known in Japan as Doitsugoi, resulted from crossing Japanese nishikigoi with German mirror carp (introduced to Japan in 1904) and are described as having large scales confined to the flanks or no scales at all; see Doitsugoi (Doitsu koi)[2]. Other named varieties produced through this breeding tradition include Asagi, Shusui (created by crossing Asagi with mirror carp), Bekko, Utsurimono, Goshiki, Hikari-mujimono (Ogon), and Kujaku[2]. According to the same source, long-finned nishikigoi (Hirenaga) developed in the 1980s through crossing with Indonesian long-finned carp are not considered genuine nishikigoi by some classifications; see Butterfly koi[2].

Breeding for hobbyists vs. professionals

Nurturing fry after spawning is described in general sources as a tricky and tedious task usually undertaken only by professional breeders[1]. A US koi dealer nonetheless presents home spawning as achievable for hobbyists, noting that many keepers breed their own fry in springtime as what it calls an “ultimate pleasure,” while cautioning that mastering sorting and culling techniques takes practice[3]. The same source lists equipment commonly assembled for hobbyist spawning attempts, including spawning ropes, a round viewing bowl, heaters and thermostats for both the spawning tank and a separate brine shrimp vessel, and air pumps with air stones[3].The Southern Regional Aquaculture Center notes that in systems aiming for the most expensive ornamental varieties, as many as 90 percent of production costs can relate to the skilled labor of grading and culling, underscoring why professional operations dominate production of top-quality nishikigoi[4]. For related background on how koi are kept once past the fry stage, see mud ponds (Niigata field ponds) and bloodlines and parent koi (oyagoi).

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Common questions

What is senbetsu in koi breeding?
Senbetsu (選別) refers to the repeated culling and grading of koi fry at different growth stages to remove individuals that lack desirable color, pattern or form, since the large majority of offspring from any spawning are not acceptable as nishikigoi[1][2].
At what water temperature do koi spawn?
General aquaculture sources describe koi spawning as water temperature approaches 68°F (20°C) and occurring mostly in early morning, while a US koi dealer describes hobbyist spawning setups using water around 75°F (24°C)[4][3].
How many eggs does a female koi produce?
Sources state that koi produce thousands of offspring from a single spawning, though the proportion later judged acceptable as ornamental nishikigoi is small, reported as under 1 percent in one Japanese-language source[1][2].
What happens to culled koi fry?
According to Wikipedia, culled fry are usually destroyed or used as feeder fish, while older culls sold within their first year at 3 to 6 inches (7.6–15 cm) long are referred to as tosai and sold as lower-grade, pond-quality koi[1].
Where did koi breeding begin?
Systematic breeding of ornamental koi began in the 1820s in the Nijūmuragō area spanning Ojiya and Yamakoshi in Niigata Prefecture, Japan[1][2].

References

  1. ^ Koi (Wikipedia). Wikipedia. en.wikipedia.org/wiki/Koi. Retrieved November 2026.
  2. ^ ニシキゴイ (Wikipedia). Wikipedia (Japanese). ja.wikipedia.org/wiki/錦鯉. Retrieved November 2026.
  3. ^ How to Breed Koi. Kodama Koi Farm (koi dealer). kodamakoifarm.com/how-to-breed-koi/. Retrieved November 2026.
  4. ^ SRAC Publication No. 7201: Species Profile: Koi and Goldfish. Southern Regional Aquaculture Center. srac.msstate.edu/pdfs/Fact%20Sheets/7201%20Species%20Profile-%20Koi…. Retrieved November 2026.
  5. ^ Male vs Female Koi Fish: How to Identify Gender and Koi Sexing Tips. Kodama Koi Farm (koi dealer). kodamakoifarm.com/male-koi-vs-female-koi-fish/. Retrieved November 2026.
  6. ^ Selective breeding (Wikipedia). Wikipedia. en.wikipedia.org/wiki/Selective_breeding. Retrieved November 2026.
  7. ^ Kin Kikokuryu: The sensational new variety. Kodama Koi Farm (koi dealer). kodamakoifarm.com/sensational-variety-kin-kikokuryu/. Retrieved November 2026.