Koi in an outdoor pond
Larger version describing the typesKoi (錦鯉; shortened from Japanese
nishikigoi) are ornamental domesticated varieties of the common carp
Cyprinus carpio.
While a Chinese book of the Western Jin Dynasty (4th century) mentions
carp with various colors, koi breeding is generally held to have begun
around the 17th century in the Niigata prefecture of Japan. Farmers working
the rice fields would notice that some carp would be more brightly colored
than others, capture them, and raise them (when normally the brighter colors
would doom the fish to be more likely eaten by birds and other predators).
By the 19th century, a number of color patterns had been established, most
notably the red-and-white kohaku, but the outside world did not become aware
of the degree of development until 1914, when the Niigata koi were exhibited
in Tokyo, and some of them presented to Crown Prince Hirohito. At that
point, interest in koi exploded throughout Japan and later worldwide. Koi
are now commonly sold in most pet stores, with higher-quality fish available
from specialist dealers.
Koi varieties are distinguished by coloration, patterning, and scalation.
Butterfly koi, developed in the 1980s and notable for their long and flowing
fins, are actually hybrids with Asian carp, and not considered true koi.
 Koi coloration includes from one to three colors, the colors including
white, yellow, orange, red, black, and blue (a grayish shade due to black
underneath the skin), with either a flat or metallic appearance. Patterning
is infinitely variable, but desirable patterns include a round patch on the
forehead, and a stepping-stone pattern down the back. The scales may be
present or missing, large or small, or crinkled, giving a "diamond"
appearance.
While possible variations are infinite, breeders have identified and
named a number of specific types. The breeding process is complicated, since
most of these varieties do not breed true, and much of the knowledge is
still a closely guarded secret. Individual fish are also selected for
appearance while being raised; the net result is that an aesthetically
attractive fish of a rare variety may fetch a price of hundreds or even
thousands of dollars.
Major koi varieties
- Asagi - light blue on top, red/orange on bottom, blue scales bordered in
white
- Shusui - similar to asagi, but with large scales in a dorsal row
- Bekko - primary color red/orange/yellow/white, with black patches
- Hikarimoyo mono - two colors; one flat, one metallic
- Hikari utsuri mono - two metallic colors
- Kawari mono - miscellaneous
- Goshiki - mostly black, with red, white, brown, and blue accents
- Kinginrin - bright metallic sheen, silver highlights
- Kohaku - red accents on white body
- Koromo - red and white overlaid with blue or silver
- Ogon - uniform yellow or white
- platinum ogon - pure white
- Showa sanke - black with red and white markings
- Taisho sanke - primarily white, with red and black markings
- Utsuri mono - uniformly black, with red, white, and yellow markings
- Tancho - primarily white, with a red patch on the forehead
- Tancho kohaku - pure white, round red head patch
Keeping koi
The common carp is a hardy fish, and koi retain that durability. They can
be kept in anything from small containers to large outdoor ponds, although
they quickly grow to 30 cm (1 ft) and can get much bigger, so the
traditional indoor aquarium is less desirable than a round plastic tub. Koi
are basically cold water fish, so it's advisable to have a half-meter or
more of depth in areas of the world that become warm during the summer.
Koi's bright colors put them at a severe disadvantage against predators;
a kohaku looks like a visual dinner bell against the dark green of a pond.
Herons, kingfishers, raccoons, cats, foxes, and badgers are all capable of
emptying a pond of its fish. A well-designed outdoor pond will have areas
too deep for herons to stand in, overhangs high enough above the water that
mammals can't reach in, and shade trees overhead to block the view of aerial
passersby. It may prove necessary to string nets or wires above the surface.
The pond should include a pump and filtration system to keep the water
clear.
Koi are bottom-feeders, so koi food is not only nutritionally balanced,
but designed to float so as to encourage them to come to the surface. Koi
will recognize the person feeding them and gather around at dinnertime. They
can even be trained to take the food from one's hand. In the winter their
digestive system slows nearly to a halt, and they eat very little, perhaps
no more than nibbles of algae from the bottom, and their appetite won't come
back until the water warms up in the spring.
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