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Koi Pond Fish
(Cyprinus carpio)

Koi, Cyprinus carpio, carp

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Koi in Japanese simply means carp. It is an all encompassing generic term. The fish commonly referred to as koi today are hybridized descendants of the common carp (Cyprinus carpio of the family Cyprinidae). Although Koi are most often associated with the Japanese, they are not indigenous to Japan. The Japanese were introduced to both the common carp and the Prussian carp (today’s goldfish) by the Chinese somewhere between 400 and 600 years ago. The domestication of both carp species dates back to the Jin Dynasty (265-420) of ancient China where they were kept in outdoor ponds and water gardens. By the time China began exporting these fish; the selective breeding of the Prusssian carp by the Chinese had already produced the colorful precursors to modern goldfish. Ironically, it was the Japanese and not the Chinese who are responsible for the selectively breeding the common carp into fish known around the world as Koi.  

Koi are known as nishikigoi (brocaded carp) in Japan. These brocaded carp are the genetically bred ornamental varieties of the common carp. While the Chinese had to some extent selectively bred this species, it was not until the 1820s that Japanese aqua-culturists began to breed them for the types of color variations that were already found in their cousins the Prussian carp. The initial breeding of modern Koi took place in the town of Ojiya on the north eastern coast of Honshu Island. The results of this selective breeding process were first revealed by fish breeder, Gonzo Hirio, in 1914 at the annual exhibition in Tokyo. The news of a new ornamental fish species quickly swept through Japan. The most popular breeds of nishikigoi in Japan fall within the category Gosanke. Gosanke breeds include Kohaku, Taisho Sanshoku, and Showa Sanshoku varieties.  


Made Public


Americanized Name

Taisho Sanshoku


White with large red and small black markings


Showa Sanshoku


Black with red and white markings



Late 19th Century

White with large red markings


New variations of Koi are still being developed. They have been bred with wild carp, Ogon Koi and several other compatible carp species producing an ever increasing spectrum of Koi offspring. It should be noted that many purists in Japan consider these latter variations as bastardized and not “true nishikigoi.” This has not diminished the enthusiasm found throughout the rest of the world. Some command quite hefty price tags among serious Koi collectors depending on their rarity and exoticism in coloration.

Goldfish have been genetically interbred for over a thousand years. Koi have only been breed for their ornamental qualities since the 1820s. If released into the wild, goldfish will continue to propagate as goldfish. Koi, however, if left on their own will revert back to their unadorned dull grey coloration in a matter of generations.  This may be the difference between a nanosecond in evolution and thousands of successive generations of selective breeding. While Koi rival or exceed the color variations found in goldfish, they lack the diversity in body types and tail configurations. These two species are so closely related to that they can and do interbreed. However the resulting offspring are very often infertile.

Koi are one of the longest lived specifies on the planet. The oldest documented koi was a scarlet Kio named Hanako.  She lived to 226 years of age (1751-July 7, 1977). Her last owner was Dr. Komei Koshihara. Her age was determined by removing one of her scales in 1966 and submitting it to extensive examination.

Today’s Koi is every bit as hardy a species as its ancient ancestors. Like goldfish, Koi are a cold water species. They thrive best in water temperature ranging from 59-77 °F. They are very active in the warmer months and enter a state of near hibernation in cold whether. In the winter months their digestive system slows to a crawl and they become quite inactive. If the temperature drops below 50 °F they are in danger of their immune systems shutting down. Consequently, Koi ponds and waterways are much deeper in areas with harsher winters than they are in more temperate zones. Areas of ponds are often heated in more severe climates. 

Koi are omnivorous. They will eat virtually anything, but should be fed a well balance diet consisting of both plant and animal matter. They will readily accept a wide variety of fruits and table vegetables including lettuce, peas, broccoli and watermelon. They can easily be trained to eat right out of your hand. They will even learn to recognize their feeder and gather around in his presence. 

On a commercial level, Koi are not typically individually breed. A female Koi lays thousands of eggs. These eggs are subject to be fertilized by multiple males. When the resulting offspring reach 3-6 inches in length they are inspected by experienced Koi masters. Unadorned fish or those with birth defects are commonly destroyed or recycle as a food product to sustain the more desirable offspring. Those who make the initial cut are then further graded from premium quality to lower grade “pond quality.” This randomized breeding technique makes it possible to create entirely new offshoots from existing varieties within just a few generations.  

Koi are generally considered too large to be kept as aquarium fish. They can easily reach an adult length in excess of four feet. This does not, however, affect their importance to the aquarium fish trade. Their interesting history and human manipulated diversity makes them a note worthy addition to this guide. 

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