Japanese colored carp, called Nishikigoi in Japan (koi for short), originated from the common carp raised as food fish by the rice farmers in Niigata Prefecture. Carp were imported from China into Japan around AD 1500, although the Chinese had been raising carp for food as early as 2000 BC. The farmers on the northwestern coast of Japan started raising common carp (Cyprinus carpio) in the irrigation reservoirs above their rice paddies. The fish would spawn in the spring and by fall the new fish would be about 4 inches (10 cm) long. These would be sun dried and salted to be eaten during the winter months. Color mutations in the young fish were first recorded in 1803, and these reddish carp were kept and added to the breeding stock. By cross-breeding the different mutations that occurred, early red and white (Kohaku), blue (Asagi), red (Higoi), and black and white (Shiro Bekko) strains were stabilized between 1830 and 1850. By the late 1880s many color varieties had been established.
Colored carp were mostly unknown outside of Niigata until Hikosaburo Hirasawa, the Mayor of Higashiyama Mura, sent 27 Nishikigoi (“brocaded carp”) to the 1914 Tokyo Taisho Exhibition as unique products of his prefecture. These fish were awarded the second prize at the exhibition, and eight of them were presented to Emperor Yoshihito’s son, Hirohito. These were placed in the moat around the emperor’s palace. Soon all of Japan wanted to keep koi, and the rest of the world followed. Koi were first exported to San Francisco in 1938, to Hawaii in 1947, to Canada in 1949, to Brazil in 1953, England in 1966, and to South Africa in 1971. Now koi are regularly imported into this country from Japanese koi farms, and from Taiwan, Hong Kong, South Africa, and Israel, as well as being bred in koi farms here in the United States.
Because of their large size (up to 1 meter in length), longevity (60 years or more), beautiful colors, friendly personalities, and high value (some champion koi have sold for over a hundred thousand dollars), koi are one of the most likely fish pets to be seen by veterinarians. A large pond of koi may have a total value exceeding several thousand to half a million dollars! Most koi owners are willing to pay an experienced aquatic veterinarian to come to the pond and check the health of their koi, and will bring the fish into the veterinary hospital for treatments, including surgical procedures.
The most important aspect in maintaining fish health is proper water quality. This depends on such things as pH (acid-base balance), temperature, alkalinity, hardness, ammonia, nitrite, nitrate, oxygen concentration, population density, and biological, chemical, and mechanical filtration systems. When all of these parameters are within their proper ranges, the fish will have less stress and be more immune to disease. Infectious and parasitic diseases occur more easily in fish stressed from improper environmental conditions. In the wild, fish may harbor a variety of parasites without incurring problems; but, if the water quality in the artificial environments of ponds or aquaria becomes abnormal, pathogens can then cause serious diseases. A combination of the environment, nutrition, genetics, and the presence of pathogens is involved in the development of disease. Anything we can do to improve these will improve the health of the fish.
In Japan, koi are spawned in ponds in the spring and the fry (baby fish) are left to grow in the ponds for the summer. In the fall, they are netted and brought into green houses for continued growth through the winter. Since koi are cold tolerant, they would survive but not grow in the ponds through the winter. By bringing them into warmer water in the green houses, they continue to grow and will reach larger sizes faster. In the ponds, a one year old koi would be 6-8 inches (15-20 cm), but in green houses they can grow to be 10-14 inches (25-36 cm).
Koi shows are part of the culture in Japan, just as we have dog shows in the US. The annual Zen Nippon Airinkai International Koi Show, held in Japan in November after the koi are brought in for the winter, is the highlight of the koi exhibitions. Each entrant has one or more show tanks to house their own fish. The koi are judged in categories determined by their size and color pattern. Winning koi are decided by their intensity of color, balance of the pattern, sharpness of the edge of the color patterns, and body conformation. Owners are awarded ribbons and trophies, and champion koi increase in value to breeders and collectors, and the reputations of the koi farmer is enhanced by the success of his koi in the shows.
In the traditional Japanese show, koi of each size and color variety were mixed together in one plastic show pond for judging. The judges would then be able to look at all of the fish being judged in that class in a single location. This made it easy for the judges to compare the merits of each fish. It also made it easy to spread diseases from one fish to another! In the English style show, now universally used since Koi Herpes Virus appeared, each koi owner is assigned one or more show ponds in which only their own fish are placed, never exposing them to other people’s koi. The judges then have to look at koi of each category spread out in many different show ponds, making their job much more arduous, but reducing the health risk to the koi. The wise koi owners will still quarantine their koi upon returning home from a show.