History
Red and white koi appeared in Japan between 1804 and 1829, when the offspring of a black carp was found to have red cheeks. She was called Hookazuki and her white offspring were bred with a Higoi, a red fish, to produce koi with red stomachs. By 1829, a koi with red gill plates called Hoo Aka had been produced, and between 1830 and 1849 several different patterns appeared, including Zukinkaburi (red forehead), Menkaburi (red head), Kuchibeni (red lips) and Sarasa (red spot on back). The breeding of Kohaku continued and varieties were improved, especially in Niigata region, now considered the birthplace of koi keeping. In about 1888, a gentleman called Gosuke bought a Hachi Hi, a red headed female, and bred it with his Sokura Kana, a cherry blossom patterned male. It is believed that the modern Kohaku was developed from the offspring of these koi.
Colors
Kohakus are white koi with red (hi) markings. Ideally, the hi should have a good depth of color but, more importantly, the color should be of a uniform shade and the edge of the hi pattern should be well defined. This definition between white and hi markings is known as "kiwa". There appear to be two types of coloration. The purplish red hi is dark and does not fade easily. This color is considered to lack elegance and tends to splatter over the koi. Brownish red hi can produce a very fine, almost translucent, color but tends to fade easily. The white should be the color of fresh snow and free from blemishes. A poor white, which can be dirty yellow in appearance, will spoil an otherwise good Kohaku because the hi pattern will not stand out.The unity and balance of color and pattern on a Kohaku are of the utmost importance. As a general guideline, the hi should cover between 50 and 70 percent of the koi.
Patterns
Because Kohaku appears as such a simple koi in terms of coloration, the criteria by which they are judged is severe. The pattern is the last thing to consider when the koi is being judged but is probably the most discussed. Balance over the whole of the koi's body is the key to any pattern.
Head
On any Kohaku the hi pattern begins on the head. The traditional head pattern for the hi is a large U shape, which should reach down as far as the eyes. If the hi does not reach the eyes, the pattern can be balanced by "kuchibeni" or lipstick like markings. A hi marking that reaches the mouth is know as "hanatsuki" and a pattern that spreads over the face is called "menkaburi". Recently, koi keepers have begun to appreciate Kohaku with interesting or irregular shaped marking on the head.
Body
Large hi markings are preferred to small hi markings. A break in the pattern is preferred between the back of the head and the shoulder. Variation is also important. Koi grow from the abdomen, so when selecting a young Kohaku, look for a large pattern of hi. Balance of pattern over the body of the koi is most important. A Kohaku that has most of its hi pattern at the front of its body lacks balance and elegance.
Patterns
Inazuma: This is a continuous pattern, extending from the head to the tail, but with a zig zag look. Inazuma literally means lightning.
Nidan: Nidan means two and this koi has two hi markings.
Sandan This Koi has three hi markings.
Yondan: This Kohaku has four hi markings.
Goten-zakura: This koi has a cherry-blossom pattern. The hi is dappled and looks like clusters of grapes.
Kanoko: This fish actually is classified in the Kawarimono class and not Kohaku in shows. The head hi is solid but the body hi is dappled.
Tail
The end of the pattern is as important as the beginning. On a perfectly marked Kohaku, the hi pattern ends just before the tail joint.
Fins
Snow white fins are the perfect accompaniment to the red on white pattern of a large koi. As a general rule, hi extending into the fins is considered detrimental to the koi's markings. Hi in the pelvic fins is not a problem because it cannot be seen when the koi is judged.
Scalation
Scalation should be even all over the body of the koi. The Japanese prefer hi that is strong enough to disguise the individual scales. Scales that are visible because the hi is thin are known as "kokesuki". A Kohaku of any pattern with scales only along the dorsal and lateral lines is known as a Doitsu Kohaku.