Common questions about koi
Questions readers often ask about koi, collected from the entries on this site. Each answer is cited; follow the entry link for the full context.
Koi varieties
How many koi varieties are there?
Zen Nippon Airinkai states there are no less than a hundred varieties when patterns are considered in detail, though it formally groups them into 17 categories for show judging.[1][2] A secondary source citing JNPA figures states there are said to be more than 140 varieties, with those outside 20 regulated types collectively called Kawarigoi.[3]
From the entry Koi varieties.
What is Gosanke?
Gosanke is the grouping of Kohaku, Taisho Sanshoku (Sanke), and Showa Sanshoku, considered the most prestigious and widely kept koi varieties.[4][5]
From the entry Koi varieties.
Do all koi organizations classify varieties the same way?
No. ZNA uses a 17-variety show system, JNPA lists its own variety set, and the American Koi Judges Association uses a related but distinct list, with show organizers permitted to adapt structures locally.[6][7][8]
From the entry Koi varieties.
What is Kinginrin?
Kinginrin, often shortened to Ginrin, refers to koi with metallic, glittering scales and occurs across versions of nearly every other named variety.[4]
From the entry Koi varieties.
Are ghost koi and butterfly koi true nishikigoi varieties?
According to Wikipedia, both ghost koi and butterfly koi were developed in the 1980s through hybridization and are considered by some not to be true nishikigoi.[4]
From the entry Koi varieties.
How many koi varieties are there?
Estimates vary by source: the Ministry of Agriculture, Forestry and Fisheries cites over 100 varieties[9], the JNPA states there are over 140[10] and elsewhere references more than 150[11], while ZNA describes no less than a hundred[1].
From the entry How koi varieties are classified.
What is the difference between ZNA's and JAS's classification?
ZNA's system is a show-judging framework with 17 varieties plus extra male categories, developed by the Zen Nippon Airinkai organization[1][2], whereas JAS 0020 is a formal Japanese Agricultural Standard enacted by the Ministry of Agriculture, Forestry and Fisheries that names 21 (now 22) varieties with legal, standardized definitions[12][13].
From the entry How koi varieties are classified.
What is Hikari-kawarigoi?
Hikari-kawarigoi (光り変わり鯉) is a variety category added to JAS 0020 in a revision effective 30 September 2026, covering koi that do not fit any other defined variety and whose whole body shines; cited examples include Beni Kikokuryu and Kogane Ochiba[14][13].
From the entry How koi varieties are classified.
Koi biology
Are koi the same species as common carp?
Historically koi were classified as Cyprinus carpio, but recent genetic and meristic studies lead many authorities to treat koi's ancestor as the separate East Asian species Cyprinus rubrofuscus, a question covered in detail on the taxonomy page[4][15].
From the entry Koi biology.
What are the whisker-like organs on a koi's face called?
They are barbels, sensory organs near the mouth that help koi taste and locate food, and they are the easiest visual way to tell a koi from a goldfish, which lacks them[16].
From the entry Koi biology.
How many fins does a koi have?
A koi has seven fins in total: one dorsal, one anal, one caudal, two pectoral and two pelvic fins[16].
From the entry Koi biology.
How long do koi live compared to goldfish?
A dealer comparison lists koi lifespan at roughly 25 to 40-plus years versus 10 to 20 years for goldfish, though individual outcomes depend on care[17].
From the entry Koi biology.
Can koi recognize their owners?
Koi can learn to associate a person's approach with feeding and may swim toward them, a behavior attributed to learning, sensory cues and conditioning rather than confirmed recognition, according to the US dealer Kodama Koi Farm[18].
From the entry Koi biology.
Is koi's scientific name Cyprinus carpio or Cyprinus rubrofuscus?
Both names appear in the literature. Older and some current sources use Cyprinus carpio[15][14], 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[4][19].
From the entry Taxonomy: Cyprinus rubrofuscus or Cyprinus carpio?.
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[19].
From the entry Taxonomy: Cyprinus rubrofuscus or Cyprinus carpio?.
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[4].
From the entry Taxonomy: Cyprinus rubrofuscus or Cyprinus carpio?.
Koi breeding
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[4][20].
From the entry Koi breeding.
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)[21][22].
From the entry Koi breeding.
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[4][20].
From the entry Koi breeding.
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[4].
From the entry Koi breeding.
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[4][20].
From the entry Koi breeding.
At what water temperature do koi spawn?
The Southern Regional Aquaculture Center reports that koi and goldfish generally spawn as water temperature approaches 68°F (20°C)[21], while the koi dealer Kodama Koi Farm describes setting up spawning ropes at around 75°F (24°C) and recommends a stable range of 65–75°F (18–24°C) to encourage spawning[22].
From the entry Spawning.
What are spawning ropes used for?
Spawning ropes and mats give koi an adhesive surface, similar to aquatic vegetation, onto which the sticky eggs can attach and be kept from clumping on the tank floor[21][22].
From the entry Spawning.
How long do koi eggs take to hatch?
Hatching time depends on temperature: Kodama Koi Farm reports about 3 days at a constant 77°F (25°C)[22], while the Southern Regional Aquaculture Center gives a range of 2 to 9 days depending on temperature, with faster hatching (46–54 hours) at 84°F (29°C)[21].
From the entry Spawning.
History of koi
When did nishikigoi breeding begin?
The JNPA dates the birth of nishikigoi to over 200 years ago in the late Edo period[11], while Wikipedia places the start of systematic breeding of ornamental Amur carp in the 1820s in the Nijūmuragō area of Niigata Prefecture[4].
From the entry History of koi.
What happened at the 1914 Tokyo Taisho Exposition?
Around twenty koi, then called “kawarigoi” or “colored carp,” were exhibited in Ueno Park and won a silver medal, after which eight were presented to the future Emperor Showa, triggering expanded sales and rising market value[11][4].
From the entry History of koi.
When was koi certified as Japan's national fish?
Nishikigoi was certified as the National Fish by the Japan Ornamental Fish Promotion Business Association in October 2022, according to the JNPA's institutional history[23].
From the entry History of koi.
How did koi become an export priority for Japan?
In December 2022 the Japanese government added koi as a key export species, following the October 2022 national fish certification and the 2017 designation of nishikigoi as the ornamental fish of Niigata[23].
From the entry History of koi.
Where did the Gosanke varieties originate?
Kohaku, Taisho Sanke, and Showa Sanshoku all trace to the Niigata region, with Kohaku fixed first in the late 19th century, Taisho Sanke during the Taisho era, and Showa introduced during the Showa period, according to the dealer Kodama Koi Farm[5]; Wikipedia dates the formal fixation of Taisho Sanshoku and Kohaku both to 1917[4].
From the entry History of koi.
What does Nijumurago mean?
Nijumurago (二十村郷, "twenty villages") is the historical name for a snowbound mountain district spanning what is now eastern Ojiya City and the Yamakoshi area of Nagaoka City in Niigata Prefecture, where ornamental koi breeding is said to have begun.[11][24]
From the entry Nijumurago: Ojiya and Yamakoshi, Niigata.
Why did nishikigoi originate in this area?
Farmers in the isolated, heavy-snow region kept common carp through the winter as a food source, and color and pattern mutations that appeared among these fish were selectively bred into what became nishikigoi.[11][25]
From the entry Nijumurago: Ojiya and Yamakoshi, Niigata.
What can visitors see at Ojiya Nishikigoi no Sato?
The facility combines an outdoor park with koi ponds, waterfalls and bridges where visitors can feed the fish, an exhibition hall covering nishikigoi history and varieties, and a viewing pool of prize specimens, with roughly 40 varieties on display.[26][27]
From the entry Nijumurago: Ojiya and Yamakoshi, Niigata.
Koi breeders and farms
Which prefecture is most associated with koi breeding in Japan?
Niigata Prefecture is the historic center of nishikigoi breeding, accounting for 43.1% of Japan's reported sales volume in 2024, with the Ojiya area alone producing about 45% of the prefecture's koi[28][26].
From the entry Koi breeders and farms.
What are considered the most prestigious koi breeders?
Sources repeatedly name Dainichi Koi Farm (Ojiya), Sakai Fish Farm (Hiroshima) and Okayama Momotaro Koi (Okayama) as breeders of grand champion koi at major Japanese shows, and the dealer Kodama Koi Farm describes Dainichi, Sakai and Momotaro as "elite breeders"[29][5].
From the entry Koi breeders and farms.
How are breeders verified or found?
The All Japan Nishikigoi Promotion Association maintains a searchable membership list of registered farms and dealers by area[30]; the association also offers a production-certificate system to help verify an individual koi's breeder and lineage[31].
From the entry Koi breeders and farms.
Has koi herpesvirus affected major breeders?
Yes; according to Kodama Koi Farm, an outbreak around 2019 affected well-known Japanese farms including Hoshikin Koi Farm and Yamacho Koi Farm, and infected fish had already been shipped internationally before cases were confirmed[32]. See koi herpesvirus (KHV) for more on the disease.
From the entry Koi breeders and farms.
What is the record price paid for a breeder's koi?
According to Koi Judges UK, the Kohaku known as S Legend, bred and sold through a Sakai auction in Hiroshima, was purchased for £1.4 million for a Chinese buyer and was Grand Champion of the 50th Anniversary Shinkokai Show in 2019[33].
From the entry Koi breeders and farms.
What was the most expensive koi ever sold at auction?
S Legend, a Kohaku bred by Sakai Koi Farm in Hiroshima, sold for 203 million yen (about £1.4 million, or $1.8 million) at a farm auction, reported by some sources as reaching 230 million yen[34][10][35].
From the entry Koi auctions.
Can I buy koi through an online auction?
Yes; dealers such as Kodama Koi Farm run ongoing online auctions with starting bids and "buy now" prices, though the All Japan Nishikigoi Promotion Association recommends buying from association-affiliated retailers because of disease risk concerns with online sales[36][10].
From the entry Koi auctions.
Do koi clubs hold their own auctions?
Many hobbyist clubs, including the Australian Koi Association, the Koi Society of Western Australia, and ZNA SoCal, hold regular or annual koi auctions for members[37][38][39].
From the entry Koi auctions.
Buying koi
Where can koi be purchased?
According to the All Japan Nishikigoi Promotion Association, koi can be bought from specialty koi shops, breeders, retailers, breeder-retailers, home improvement stores, pet shops and online, though the association recommends buying from its affiliated retail stores.[10]
From the entry Buying koi.
How much should a beginner spend on a first koi?
The US importer Kodama Koi Farm suggests beginners typically spend $45 to $150 per koi when starting with smaller, younger fish or mixed packs before investing in higher-quality fish.[35]
From the entry Buying koi.
Do new koi need to be quarantined?
Kodama Koi Farm strongly recommends quarantining every new koi, suggesting a tank of 100–300 gallons, a water temperature of at least 72°F, and salt at 0.3% concentration, with a KHV-focused quarantine of at least four weeks.[40][41]
From the entry Buying koi.
What is the difference between Japanese and domestic koi?
Kodama Koi Farm describes Japanese koi as bred in Japan with generations of lineage and considered the highest quality, while domestic koi are bred outside Japan, sometimes from broodstock originally imported from Japan.[42]
From the entry Buying koi.
How many koi varieties exist?
The JNPA states there are over 140 varieties of Nishikigoi, officially grouped into 22 show categories recognized as Japanese Agricultural Standards, while Kodama Koi Farm cites over 100 officially recognized varieties.[10][35]
From the entry Buying koi.
What does tosai mean in koi terminology?
Tosai refers to a koi in its first year, born that year, according to the American Koi Judges Association glossary[43], a stage the All Japan Nishikigoi Promotion Association calls “tosaigyo” from hatching until about one year old[10].
From the entry Age terms: tosai, nisai, sansai and yonsai.
What is a nisai koi?
Nisai means a koi born the previous year, effectively in its second year[43], and the All Japan Nishikigoi Promotion Association recommends nisaigyo for first-time koi owners[10].
From the entry Age terms: tosai, nisai, sansai and yonsai.
How big should a sansai or yonsai koi be?
According to a growth timeline published by the dealer Kodama Koi Farm, sansai (year three) koi average about 20–26 inches and yonsai-stage koi fall within the broader adult range of roughly 24–32 inches by three to six years old, though actual size depends heavily on pond conditions and feeding[44].
From the entry Age terms: tosai, nisai, sansai and yonsai.
Koi ponds
How deep should a koi pond be?
Koi ponds usually have at least a meter of depth where summers are warm, and a minimum of about 1.5 m (5 ft) in regions with harsh winters, since koi’s immune systems weaken sharply below 10 °C (50 °F).[4] Some sources describe winter depths of 3 to 5 feet so koi can swim beneath an ice layer without the pond freezing solid.[45]
From the entry Koi ponds.
Does a koi pond need a filter?
Most dedicated koi ponds use a pump and filtration system to keep water clear and manage fish waste through the nitrogen cycle, though lightly stocked, heavily planted water gardens may not strictly require filtration.[45][46]
From the entry Koi ponds.
How do I calculate how many koi my pond can hold?
Pond volume is calculated by multiplying surface area by average depth, and a commonly cited general rule is no more than 1 pound of adult fish per 100 gallons of water, though koi can grow much larger than this rule-of-thumb example implies, so stocking should account for adult size.[47][46]
From the entry Koi ponds.
Should UV or ozone be used to control pond algae?
According to the koi dealer Kodama Koi Farm, UV clarifiers are generally simpler and sufficient for most residential ponds focused on controlling green water, while ozone systems offer broader treatment capability but need more specialized equipment and monitoring.[48]
From the entry Koi ponds.
Can a koi pond be built indoors or on a balcony?
Yes; the All Japan Nishikigoi Promotion Association describes keeping koi in balcony tanks or indoor fish tanks with an appropriately sized filtration system, air pump and sunshade, noting that this has become increasingly popular in apartments and condominiums.[49]
From the entry Koi ponds.
How deep should a koi pond be?
Sources vary: some water garden guidance allows 18 to 24 inches in warm climates with light stocking, while koi-specific sources recommend 3 to 5 feet, or ideally 4 to 6 feet or more, so koi have a stable, cool retreat and protection from freezing and predators[50][45][44].
From the entry Pond design: size, depth and volume.
How do I calculate my pond's volume in gallons or liters?
Volume equals surface area multiplied by average depth; for rectangular or circular shapes simple geometric formulas apply, and cubic inches can be converted to gallons (×0.00433) or liters using standard conversion tables, or volume can be estimated using a salt/chloride concentration test[47][51].
From the entry Pond design: size, depth and volume.
How many koi can I keep per gallon or liter?
General ornamental pond guidance suggests no more than 1 pound of fish per 100 gallons of water without good filtration, rising to about 2 pounds per 100 gallons with strong aeration and filtration, though top Japanese exhibitors reportedly stock only 10 to 15 koi even in large water gardens[46][50].
From the entry Pond design: size, depth and volume.
Koi pond equipment
Do all koi ponds need a filter?
Not necessarily: ornamental ponds and water gardens with large quantities of plants and a modest number of fish may not require filtration because plants act as active biological filters, though dedicated koi ponds commonly use a circulation filtration system[46][49].
From the entry Koi pond equipment.
Should koi pond equipment run during winter?
According to the dealer Kodama Koi Farm, pond pumps and filters are commonly stopped during winter dormancy to avoid disturbing hibernating koi, while air pumps are kept running to maintain a hole in the ice and aid de-gassing[52].
From the entry Koi pond equipment.
Is UV or ozone better for a koi pond?
For most residential koi ponds, Kodama Koi Farm states UV is simpler and more practical for controlling green water, while ozone offers broader oxidation but requires more equipment and careful residual control[48].
From the entry Koi pond equipment.
What does a bottom drain do?
A bottom drain carries heavy solids settling on the pond floor to the mechanical filter and, in many designs, also includes air diffusers that add oxygen to the pond[45].
From the entry Koi pond equipment.
Why is aeration important for koi?
Warm water holds less dissolved oxygen while fish and microorganisms demand more of it, so aeration helps maintain the oxygen supply, particularly overnight when plants and algae also consume oxygen[53][54].
From the entry Koi pond equipment.
What is the difference between mechanical and biological filtration in a koi pond?
Mechanical filtration physically traps solid waste such as uneaten food and feces using a sieve-like material, while biological filtration provides surfaces for nitrifying bacteria that convert toxic ammonia into nitrite and then into less toxic nitrate.[45][55]
From the entry Pond filtration explained.
How long does it take to establish a new biofilter?
A new biofilter generally requires six to eight weeks to build up enough nitrifying bacteria to effectively reduce ammonia and nitrite levels.[56]
From the entry Pond filtration explained.
Do all ponds need filtration equipment?
Not necessarily; ponds with abundant plants and a modest number of fish can rely on plants as biological filters, but ponds stocked more heavily, as is typical with koi, generally need dedicated mechanical and biological filtration.[46]
From the entry Pond filtration explained.
Water quality
What are the most important water quality parameters for a koi pond?
Core parameters cited by aquaculture extension sources are ammonia, nitrite, nitrate, pH, alkalinity, dissolved oxygen and temperature, with hardness and chlorine also relevant depending on water source[57][58].
From the entry Water quality.
What dissolved oxygen level do koi need?
A concentration of 5 mg/L or more dissolved oxygen is recommended for optimum fish health, with distress common at 2–4 mg/L and mortality typically below 2 mg/L[59].
From the entry Water quality.
Why does ammonia become more dangerous at higher pH?
Ammonia exists partly as toxic un-ionized ammonia (NH3) and partly as less toxic ionized ammonium (NH4+); the proportion of the toxic form increases roughly tenfold for each one-unit rise in pH[60][61].
From the entry Water quality.
What causes nitrite to build up in a pond?
Nitrite accumulates when ammonia is oxidized faster than nitrite-oxidizing bacteria can convert it to nitrate, which is more likely in closed or intensive systems with insufficient filtration, and during fall and spring temperature fluctuations[62].
From the entry Water quality.
Is nitrate dangerous to koi?
Nitrate has traditionally been considered non-toxic even up to 200 mg/L, but more recent research suggests it may be more harmful than previously believed, and it can accumulate above 250 mg/L in closed systems with little water exchange[56].
From the entry Water quality.
What bacteria are responsible for the nitrogen cycle in a koi pond?
Ammonia-oxidizing bacteria, commonly identified as Nitrosomonas, convert ammonia to nitrite, and nitrite-oxidizing bacteria, commonly identified as Nitrobacter (with Nitrospira also cited in some sources), convert nitrite to nitrate[56][55][63].
From the entry The nitrogen cycle.
How long does it take to establish the nitrogen cycle in a new pond or filter?
A new biofilter typically requires six to eight weeks to build up enough nitrifying bacteria to effectively reduce ammonia and nitrite[56][55].
From the entry The nitrogen cycle.
Why is ammonia dangerous if it cannot be seen or smelled?
Ammonia is colorless and odorless even at levels toxic to fish, so testing water parameters is the only reliable way to detect it before it harms koi[56].
From the entry The nitrogen cycle.
Feeding koi
How often should koi be fed?
General aquaculture guidance suggests feeding around 0.5–1.0% of body weight per day for maintenance, often as a single daily feeding, though young fish need smaller, more frequent meals[64]. The dealer Kodama Koi Farm recommends 2–4 small feedings per day to support growth[44].
From the entry Feeding koi.
Should koi be fed in winter?
Feeding is not recommended once water temperature drops below 10 °C (50 °F), since koi digestion slows nearly to a halt and they eat very little[4]. A dealer source states feeding should be reduced or stopped depending on temperature during winter[44].
From the entry Feeding koi.
What protein level should koi food contain?
Protein needs vary by life stage; aquaculture research notes fry and fingerling diets often exceed 50% crude protein while maintenance diets may be 25–35%[64]. A koi dealer recommends 30–40% protein food for juvenile, rapidly growing koi[65].
From the entry Feeding koi.
Can koi eat fruit and vegetables as treats?
Yes, koi are omnivorous and commonly eat items such as peas, lettuce, and watermelon in addition to commercial food[4].
From the entry Feeding koi.
Is hand feeding koi beneficial?
According to the dealer Kodama Koi Farm, hand feeding allows closer observation of koi health and behavior, provides enrichment, and can be a bonding experience, though overfeeding should be avoided[66].
From the entry Feeding koi.
What is the difference between floating and sinking koi food?
Floating pellets let keepers watch koi feed at the surface and check them for parasites or ulcers, while sinking food suits koi's natural bottom-feeding tendency; some products combine both forms.[4][64]
From the entry Koi food types.
What protein percentage should koi food contain?
Omnivorous fish such as koi are generally reported to need about 25–35% crude protein, with higher levels (sometimes over 50%) used in starter foods for young, fast-growing fish.[67][64]
From the entry Koi food types.
Why do some koi foods use wheat germ?
Wheat germ-based foods are marketed as digestible options as water cools, and raw wheat germ is described by the US importer Kodama Koi Farm as supplying natural vitamin E linked to immune support and skin luster.[68]
From the entry Koi food types.
Seasonal koi care
At what temperature should koi feeding stop in winter?
Kodama Koi Farm states that koi should not be fed once water temperature drops below 50°F (10°C) because they cannot properly digest food, though some foods are marketed as digestible down to 45°F (7°C)[52].
From the entry Seasonal koi care.
Why are spring and autumn considered risky for koi?
Fluctuating water temperatures in these transition seasons can stress koi and increase susceptibility to parasites and disease, and University of Florida IFAS Extension notes that koi herpesvirus outbreaks typically occur in spring and autumn[52][69].
From the entry Seasonal koi care.
Should a koi pond be covered in winter?
Kodama Koi Farm recommends covering a koi pond in winter to retain warmth and keep debris out, suggesting options such as a greenhouse frame or a pool-style solar cover held down with weighted objects[52].
From the entry Seasonal koi care.
How should feeding change during a summer heat wave?
Kodama Koi Farm advises reducing feeding quantity once water reaches around 28°C (82°F) and above, and stopping feeding entirely if koi show poor feeding response or respiratory distress, since uneaten food adds to biological load and lowers oxygen levels[70].
From the entry Seasonal koi care.
Does koi growth continue year-round?
No; according to Kodama Koi Farm, growth is fastest in summer, slows during autumn conditioning, nearly stops in winter maintenance mode, and accelerates again in spring as metabolism rises with temperature[44].
From the entry Seasonal koi care.
At what temperature should koi feeding resume in spring?
Wikipedia states that feeding is not recommended below 10°C (50°F) and that koi appetite does not return until the water warms in spring[4]; Kodama Koi Farm describes roughly 65–68°F as a key turning point for adjusting feeding programs[52].
From the entry Spring care.
Why are koi more vulnerable to parasites in spring?
UF/IFAS Extension notes that Ich outbreaks often appear when water temperatures are changing rapidly, and that in spring the parasite's life cycle proceeds faster in warming water, increasing infection risk[71].
From the entry Spring care.
Is spring viremia of carp (SVC) treatable?
No treatment for SVC is known, according to Wikipedia, so prevention and biosecurity are emphasized by sources such as UF/IFAS Extension[4][72].
From the entry Spring care.
Koi health and disease
What is the single most important factor in preventing koi disease?
Sources emphasize that good water quality management, proper nutrition, and sanitation form the foundation of disease prevention, since medications cannot substitute for proper husbandry[58].
From the entry Koi health and disease.
How long should new koi be quarantined?
A fish health extension source recommends quarantine lasting through the full range of seasonal water temperatures at which a disease of concern can be detected[73], while the US dealer Kodama Koi Farm recommends at least 21 days to 2–4 weeks for newly purchased koi[40][65].
From the entry Koi health and disease.
Can stress alone make a koi sick?
Stress itself does not directly cause infectious disease but compromises the mucus, skin, and immune barriers that normally protect koi, making them more susceptible to pathogens already present in the water[74][75].
From the entry Koi health and disease.
Should a sick koi be treated at home or seen by a professional?
Extension sources recommend contacting a fish health specialist or veterinarian, especially for suspected bacterial or viral disease, since laboratory culture and sensitivity testing are needed to identify the cause and choose an effective treatment[58][76].
From the entry Koi health and disease.
Are viral koi diseases treatable with medication?
No specific medications cure viral infections of fish; diagnosis requires specialized laboratory tests, and management focuses on prevention, biosecurity, and supportive care rather than curative drugs[58][69].
From the entry Koi health and disease.
What does it mean if a koi is flashing or rubbing against the pond?
Flashing, where a koi rubs or scrapes its body against the pond bottom or sides, can indicate skin irritation from parasites, poor water quality, or other environmental problems; occasional flashing may not be serious, but frequent flashing should prompt a water-quality check.[18] Several koi flashing and swimming erratically together is often linked to parasites.[77]
From the entry Signs of illness.
Why do koi jump out of the water?
According to Kodama Koi Farm, koi may jump because of parasites, poor water quality, stress, sudden disturbances, or a lack of oxygen; occasional jumping can be natural, but repeated jumping may signal irritation or stress requiring a check of water quality and aeration.[18]
From the entry Signs of illness.
Is gasping at the surface always a sign of low oxygen?
Gasping at the surface is associated with low dissolved oxygen, which the University of Florida IFAS Extension identifies as a frequent cause of mortality especially in warm water, but it can also reflect gill disease or gill infection, as noted by Kodama Koi Farm, so water quality and gill condition should both be checked.[58][78]
From the entry Signs of illness.
Predators of koi
What animals prey on koi?
Sources list herons, kingfishers, otters, raccoons, skunks, mink, cats, foxes and badgers as animals capable of spotting and eating koi[4], while aquaculture literature also documents cormorants, pelicans, egrets and other wading birds as fish predators at ponds[79].
From the entry Predators of koi.
How can a pond be designed to reduce predation?
A well-designed pond includes areas too deep for herons to stand in, overhangs too high for mammals to reach into, and shade trees to block aerial view, with netting or wires sometimes strung above the surface[4]; a minimum depth of around 3 feet (about 0.9 m) is also recommended to give fish a safe retreat from birds and land predators like raccoons[46].
From the entry Predators of koi.
Is koi theft a common problem?
According to the US importer Kodama Koi Farm, koi theft is uncommon but can occur, particularly where ponds are easily visible or accessible from outside the property, and owners of valuable collections may want to take additional precautions such as cameras, lighting and record-keeping[80].
From the entry Predators of koi.
Can bird predators be legally killed?
Most fish-eating birds in the United States are protected under the Migratory Bird Treaty Act and generally cannot be killed without a depredation permit from the US Fish and Wildlife Service, and some species such as Wood Storks and eagles have additional legal protections restricting control measures[81].
From the entry Predators of koi.
Do otters and mink actually eat koi, or mostly wild fish?
General sources list otters and mink among animals capable of eating koi[4], and both are also documented predators of common carp[15]; North American river otters are described as favoring fish such as perch, suckers and catfish[82], while American mink diets are dominated by small mammals, with fish as a secondary component[83].
From the entry Predators of koi.
Do herons actually eat koi?
Yes; both grey herons and great blue herons are recognized fish predators that forage in shallow water, and garden ponds stocked with ornamental fish are described as attractive, easy sources of prey, particularly for young birds learning to hunt[84][85].
From the entry Herons.
Is it legal to kill a heron that is eating koi?
In the United States, great blue herons and other fish-eating birds are protected under the Migratory Bird Treaty Act, and a depredation permit from the U.S. Fish and Wildlife Service is required before any lethal control[81]. In the United Kingdom, the grey heron has Green conservation status according to the RSPB[86].
From the entry Herons.
What deterrents are used against herons at fish ponds?
Aquaculture guidance describes dispersal techniques such as propane exploders, spotlights, strobe lights, and lasers aimed at roosting or feeding birds, timed around feeding periods when fish are near the surface[81].
From the entry Herons.
Koi laws and regulations
Is koi herpesvirus (KHV) a notifiable disease?
Yes. In England and Wales, KHV is a “Listed” (notifiable) disease that must be reported immediately to the Fish Health Inspectorate, Cefas, under the Aquatic Animal Health (England and Wales) Regulations 2009[87]. In the United States, University of Florida IFAS Extension describes KHV as notifiable to USDA APHIS Veterinary Services and the relevant state veterinarian[69].
From the entry Koi laws and regulations.
Do I need a permit to import koi into the UK?
Yes. Importers need authorization from the Fish Health Inspectorate (FHI), Cefas, and must meet certification and pre-notification requirements through the IPAFFS system; there is no fee for applying, but importing without authorization can result in an unlimited fine[88].
From the entry Koi laws and regulations.
Are koi illegal to own in some places?
In Victoria, Australia, koi carp are listed as a noxious aquatic species, and it is illegal without a permit to import, keep, sell, trade, transport, or possess them[89]. New Zealand’s Department of Conservation also treats koi carp as an animal pest[90].
From the entry Koi laws and regulations.
Can KHV-vaccinated koi be imported anywhere?
Not necessarily; University of Florida IFAS Extension notes that some countries’ import requirements specifically exclude KHV-vaccinated fish from entry, so breeders and dealers should check APHIS and destination-country requirements before shipping[69].
From the entry Koi laws and regulations.
Does the Lacey Act apply to koi shipments within the US?
Yes. According to the Southern Regional Aquaculture Center, the Lacey Act is a federal law regulating interstate transportation of live fish, and proper permits must accompany each load along with required paperwork and signage[91].
From the entry Koi laws and regulations.
Is koi herpesvirus (KHV) notifiable everywhere?
KHV is a listed, notifiable disease in the United Kingdom, where it must be reported to the Fish Health Inspectorate immediately[87]. In the United States, UF/IFAS EDIS describes KHV reporting obligations to state officials, while a separate SRAC fact sheet states KHV is not a reportable disease there, so requirements should be confirmed locally[69][21].
From the entry Notifiable koi diseases.
Is spring viremia of carp (SVC) notifiable?
Yes. SVC is listed by WOAH as notifiable and is reportable in the United States to USDA APHIS, federally reportable in Canada to the CFIA, and notifiable in the UK[72][92][93].
From the entry Notifiable koi diseases.
Is carp pox a notifiable disease?
No. According to UF/IFAS EDIS, carp pox (Cyvirus cyprinidallo1) is not a reportable or notifiable disease in the United States, unlike KHV and SVC[69].
From the entry Notifiable koi diseases.
Koi clubs and associations
What is the difference between ZNA and JNPA?
Zen Nippon Airinkai (ZNA) is a Japanese organization authorized as an Ippan Shadan Hojin focused on promoting nishikigoi keeping, judging standards, and international chapters, founded by Dr. Kuroki Takeo.[94] The All Japan Nishikigoi Promotion Association (JNPA) is composed of koi breeders and dealers and focuses on production, sales, and breeding information, holding its own set of annual shows.[95][96]
From the entry Koi clubs and associations.
Is the Nishikigoi Vereniging Nederland affiliated with ZNA?
Yes, the NVN is listed by Zen Nippon Airinkai as its Dutch Chapter.[97]
From the entry Koi clubs and associations.
What happened to the British Koi-Keepers Society?
According to its own website, the British Koi-Keepers Society (BKKS) has closed after 50 years, is not currently inviting new memberships, and a separate National Koi Show website was expected to launch.[98]
From the entry Koi clubs and associations.
How large is the JNPA?
As of the end of June 2024, JNPA reported 299 domestic members in Japan and 223 overseas members, for a total of 522.[96]
From the entry Koi clubs and associations.
Which show does the NVN organize?
The NVN organizes the Holland Koi Show, which it describes as the largest koi show in the world, along with a Young Holland Koi Show; the main show moved to Appeltern as announced in April 2024.[99]
From the entry Koi clubs and associations.
When was Zen Nippon Airinkai founded?
ZNA's predecessor, Oita Airinkai, was founded on 11 February 1962 in Beppu, Oita, and the organization became the nationwide Zen Nippon Airinkai on 11 May 1968.[94][100]
From the entry Zen Nippon Airinkai (ZNA).
Who founded ZNA?
ZNA was founded by Dr. Kuroki Takeo, MD, who led the organization as chairman from 1962 to 1991.[94][100]
From the entry Zen Nippon Airinkai (ZNA).
How many koi varieties does ZNA recognize for shows?
For appreciation and show entry, ZNA divides nishikigoi into 17 varieties grouped into two judging groups for its Zipangu Prize, plus six extra categories for large male koi, even though it recognizes that over a hundred varieties exist overall.[1]
From the entry Zen Nippon Airinkai (ZNA).
Koi shows
What are koi judged on at a show?
According to the All Japan Nishikigoi Promotion Association, koi are judged on body shape, quality and pattern, with body shape — a solid skeletal structure and plump form — given particular emphasis.[10]
From the entry Koi shows.
What are the three major national koi shows in Japan?
The JNPA names the All Japan Combined Nishikigoi Show, the Nishikigoi All Japan Young Koi Show, and the International Junior Koi Show as its three major competitions, alongside regional District and Prefectural shows.[10]
From the entry Koi shows.
Are butterfly koi allowed to compete in koi shows?
According to a secondary source, Zen Nippon Airinkai and the UK Koi Judges Association have historically excluded butterfly koi from competitive judging, while the American Associated Koi Clubs of America reportedly introduced standards for judging them as of 2006.[101]
From the entry Koi shows.
Is entry to Japanese koi shows free?
The JNPA states that most of its competitions, including the District and Prefectural shows, are free to attend.[10]
From the entry Koi shows.
Where can I find upcoming koi show dates?
Sources with published schedules include the JNPA's show schedule page for Japan[102], the ZNA show calendar for Japanese chapter shows[103], the American Koi Judges Association's US show list[104], and Koi Judges UK's schedule for the UK and Europe[105].
From the entry Koi shows.
What are the main criteria used to judge koi?
The All Japan Nishikigoi Promotion Association describes four criteria: body shape, quality, finish, and pattern, with body shape considered the most important.[106] A separate JNPA Q&A page groups the criteria as body shape, quality, and pattern.[10]
From the entry How koi are judged.
Why are koi viewed from above when judged?
Judging is done from a top-down angle because the ideal koi shape is generously oval when viewed that way, unlike a side profile; a secondary account compares this to a "beauty pageant" where judges instead want a plump rather than slim appearance.[101][107]
From the entry How koi are judged.
Can butterfly koi be judged in traditional koi shows?
No; ZNA and the UK Koi Judges Association have disallowed butterfly koi from traditional competitive judging because their slender conformation and larger fin-to-body ratio do not fit standard criteria, though the American Associated Koi Clubs of America reportedly developed separate standards for them.[101]
From the entry How koi are judged.
Koi vs goldfish
Can koi and goldfish interbreed?
Yes, koi and goldfish can interbreed, but because they belong to different genera the resulting offspring are sterile.[4][17]
From the entry Koi vs goldfish.
What is the easiest way to tell a koi from a goldfish?
According to the koi dealer Kodama Koi Farm, barbels, the whisker-like sensory organs near the mouth, are the easiest distinguishing feature: koi have them and goldfish do not.[16]
From the entry Koi vs goldfish.
Do koi and goldfish come from the same wild ancestor?
No; most ornamental koi descend from Amur carp (Cyprinus rubrofuscus) bred in Japan, while goldfish were selectively bred in China from Prussian carp or related Carassius species, according to Wikipedia and the koi dealer Kodama Koi Farm.[4][17]
From the entry Koi vs goldfish.
Can koi and goldfish live together in the same pond?
According to the koi dealer Kodama Koi Farm, koi and goldfish can coexist in large, well-filtered ponds, but keepers should monitor them because koi grow faster and may outcompete or injure smaller goldfish during feeding or spawning.[17]
From the entry Koi vs goldfish.
Are koi and goldfish equally susceptible to koi herpesvirus?
No; University of Florida IFAS Extension reports that koi herpesvirus disease has been diagnosed in koi and common carp, while goldfish typically do not show disease signs even though they can carry and spread the virus.[69]
From the entry Koi vs goldfish.
Koi vs common carp and wild carp
Are koi and common carp the same species?
Sources differ: Kodama Koi Farm and the Texas A&M AgriLife Extension describe koi and common carp as the same species, Cyprinus carpio[108][46], while Wikipedia notes that recent genetic studies place koi's ancestry closer to the East Asian species Cyprinus rubrofuscus rather than the European common carp[4][19].
From the entry Koi vs common carp and wild carp.
What is magoi?
Magoi (真鯉, “true carp”) is the Japanese name for the black carp from which koi were selectively bred, also referred to as nogoi (野鯉, “wild carp”)[4][25].
From the entry Koi vs common carp and wild carp.
Can koi revert to wild carp coloration?
According to Wikipedia's Japanese garden article, koi are domesticated common carp selected for color and will revert to original (drab) coloration within a few generations if allowed to breed freely[109].
From the entry Koi vs common carp and wild carp.
Do koi and carp grow to similar sizes?
Reported maximums vary by source: Kodama Koi Farm states wild carp can reach up to 4 feet and koi up to 3 feet[108], while FishBase and Wikipedia report common carp maximum lengths around 120–129 cm (about 47–51 in)[110][15].
From the entry Koi vs common carp and wild carp.
Is wild carp considered an invasive species?
Wikipedia notes common carp is often considered invasive and appears on a list of the world's 100 worst invasive species, even though native wild populations are assessed as vulnerable by the IUCN[15]; FishBase lists the overall species as Least Concern but a potential pest[110].
From the entry Koi vs common carp and wild carp.
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