Butterfly Koi, Longfin Koi, or Dragon Carp are a type of ornamental fish notable for their elongated finnage. The fish are a breed of the common carp, Cyprinus carpio, which includes numerous wild carp races as well as domesticated koi ("Nishikigoi").

Butterfly Koi originated in the mid-20th century as a result of an effort to increase the hardiness of traditional koi. Japanese breeders interbred wild Indonesian Longfin river carp with traditional koi. The resulting fish had longer fins, long barbells, pompom nostrils, and were hardier than koi. These were known in Japan as "onagaoi" or "hire naga koi", or translated in English "long tail koi". Randy LeFever, the son of Wyatt LeFever, a noted breeder of koi, is credited with suggesting they looked like butterflies, a trait for which the breed is named. They are also sometimes referred to as Dragon Koi.

Nishikigoi Judging

Butterfly koi cannot be judged using the traditional criteria of used for koi judging. The standard criteria used in these events has evolved over many years, and they are specifically tailored to rate the characteristics of koi. According to an article in KOI USA magazine, the following characteristics are largely the basis for the unsuitability of butterfly koi in traditional competition.

Conformation - The ideal shape of a koi has been set by tradition to be generously oval. By contrast, butterfly koi are naturally more slender. This difference is amplified by the fact that traditional koi judging is done from a top-down viewing angle.

Relationship Of Fin To Body – The ratio of fin-to-body is an important scoring criteria in nishikigoi competitions. By design, Longfin embody a ratio that exceeds the standards applied to nishikigoi by 500 to 1000 percent.

Pattern Differences - Great energy has been given to developing butterfly koi versions of traditional koi patterns, (eg: kohaku, sanke, showa, utsuri and ogon). Butterfly koi, however, exhibit these patterns in a slightly different way.

For these reasons, Japan’s airinkai (an organization that sanctions Japanese nishikigoi hobbyist competitions) have disallowed butterfly koi from competitive judging for many years, although their American counterpart the American Koi Club Association (AKCA) has (as of June, 2006) reportedly created new standards for judging butterfly koi at future AKCA competitions if you are showing thw butterfly koi show only females.

Popularity

Butterfly koi are strongly disliked by many keepers of traditional koi who view the breed as inferior to koi. This polarization of traditional keepers may be the reason why some koi retailers do not sell butterfly koi, and why many of Japan’s famous and most prestigious breeders do not breed butterfly koi today. They are largely unpopular in Europe and Asia, but are popular in the United States where they are more readily available. The popularity of these fish in the United States has earned them the nickname American Koi.

Health, maintenance and longevity

The common carp is a hardy fish, and koi retain that durability. Koi are cold-water fish, but benefit from being kept in the 15-25 °C (59-77°F) range, and do not react well to long, cold, winter temperatures; their immune systems "turn off" below 10°C. Koi ponds usually have a meter or more of depth in areas of the world that become warm during the summer, whereas in areas that have harsher winters, ponds generally have a minimum of 1.5 meters (4½ feet). Specific pond construction has evolved by koi keepers intent on raising show-quality koi.

Koi's bright colors put them at a severe disadvantage against predators; a white-skinned Kohaku is a visual dinner bell against the dark green of a pond. Herons, kingfishers, otters, raccoons, cats, foxes, badgers and hedgehogs are all capable of emptying a pond of its fish. A well-designed outdoor pond will have areas too deep for herons to stand, overhangs high enough above the water that mammals cannot reach in, and shade trees overhead to block the view of aerial passers-by. It may prove necessary to string nets or wires above the surface. A pond usually includes a pump and filtration system to keep the water clear.

Koi are an omnivorous fish, and will eat a wide variety of foods, including peas, lettuce, lemons and watermelon. Koi food is designed not only to be nutritionally balanced, but also to float so as to encourage them to come to the surface. When they are eating, it is possible to check koi for parasites and ulcers.

Koi will recognize the persons feeding them and gather around them at feeding times. They can be trained to take food from one's hand. In the winter, their digestive systems slow nearly to a halt, and they eat very little, perhaps no more than nibbles of algae from the bottom. Care should be taken by hobbyists that proper oxygenation and off-gassing occurs over the winter months in small water ponds, so they do not perish.

Their appetites will not come back until the water becomes warm in the spring. When the temperature drops below 50°F (10°C), feeding, particularly with protein, is halted or the food can spoil in their stomachs, causing sickness and death.

One famous scarlet koi, named "Hanako" (c. 1751 – July 7, 1977) was owned by several individuals, the last of whom was Dr. Komei Koshihara. Hanako was supposedly 226 years old upon her death, based on examining one of her scales in 1966. Koi "maximum longevity" is listed as 47 years old.

Breeding

Koi Outdoor Koi Pond

Like most fish, koi reproduce through spawning in which a female lays a vast number of eggs and one or more males fertilize them. Nurturing the resulting offspring (referred to as "fry") is a tricky and tedious job, usually done only by professionals. Although a koi breeder may carefully select the parents they wish based on their desired characteristics, the resulting fry will nonetheless exhibit a wide range of color and quality.

Koi will produce thousands of offspring from a single spawning. However, unlike cattle, purebred dogs, or more relevantly, goldfish, the large majority of these offspring, even from the best champion-grade koi, will not be acceptable as nishikigoi (they have no interesting colors) or may even be genetically defective. These unacceptable offspring are culled at various stages of development based on the breeder's expert eye and closely guarded trade techniques. Culled fry are usually destroyed or used as feeder fish (mostly used for feeding arowana due to the belief it will enhance its color), while older culls, within their first year between 3" to 6" long (also called "Tosai"), are often sold as lower-grade, pond-quality koi.

The semirandomized result of the koi's reproductive process has both advantages and disadvantages for the breeder. While it requires diligent oversight to narrow down the favorable result the breeder wants, it also makes possible the development of new varieties of koi within relatively few generations.

In the wild

Koi have been accidentally or deliberately released into the wild in every continent except Antarctica. They quickly revert to the natural coloration of common carp within a few generations. In many areas, they are considered an invasive species and pests. They greatly increase the turbidity of the water because they are constantly stirring up the substrate.

This makes waterways unattractive, reduces the abundance of aquatic plants, and can render the water unsuitable for swimming or drinking, even by livestock. In some countries, koi have caused so much damage to waterways that vast amounts of money and effort have been spent trying to eradicate them, largely unsuccessfully.

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