What is a koi carp?

The koi (Cyprinus carpio carpio), also called Nishikigoi or brocade carp, is the national fish of Japan. “Nishiki” is the Japanese word for “colorful rug,” while “Goior Koi” means “carp.” The koi is a breeding variety of the common carp (Cyprinus carpio) and enjoys – especially in recent years – a great popularity in ornamental ponds. The taxonomic status of the species is uncertain. The Japanese wild carp are Cyprinus rubrofuscus or Cyprinus carpio rubrofuscus. The tendency nowadays is to split the species. For breeding, koi are crossed with German mirror carp (Cyprinus carpio carpio), so the koi with the irregular cuticle pattern of the mirror carp are hybrids.


Although a Chinese book from the Jin Dynasty (4th century) mentions the koi as a brightly colored carp, it is believed that the breeding of koi as ornamental fish would have started in the 19th century in the Japanese prefecture of Niigata, when rice farmers discovered that some carp were more beautiful were colored than others. The striking carp were caught and bred separately. In the 20th century, a number of color variants were set as the norm, in particular the white-red Kohaku. These standards were not known to the outside world until 1914, when the Niigata Koi were exhibited at the Tokyo Fair. Some koi were then given to crown prince Hirohito.

As transport times were shortened and storage options – including the arrival of plastic bags – improved, the worldwide spread of Japanese koi became a fact. In Europe, the United Kingdom was the first country where the koi hobby set foot on the ground. But other countries soon followed, including the Netherlands, Belgium and Germany. Estimates about the number of koi ponds in the Netherlands and Belgium range from 50,000 to even 400,000.

Koi varieties

Koi varieties are distinguished by their colors, patterns and mutual relationships.

In principle, only koi that are grown in Japan deserve the term “Japanese koi.” Although Niigata is still one of the most important koi producing districts, the areas around Yamanashi and Hiroshima are on the rise. Breeding variants from Europe and from Israel, which are growing in popularity, are called Eurokoi and Israeli koi respectively. The Vlinderkoi (Butterfly Koi) or Hyrenaga, which was cultivated in the 80s and stands out for its long streamlined fins, are in fact hybrids of the Asian carp and are not generally accepted as “real koi”. Since a few years, the koi grown in Taiwan, Thailand and Malaysia have also been on the rise in European countries. The seasoned hobbyist, however, remains faithful to his Japanese koi.

Buying a Koi carp

Buying koi carps is a very nice activity. However, it should not be thought too lightly. Keeping koi entails various responsibilities. There are several things that require attention before the koi are purchased. A few points of interest are, for example, the pond capacity, the time of purchase, the reliability of a seller and the transport of a koi carp.

Koi Ponds

Building or making a koi pond means that the special requirements for koi must be taken into account. Keeping koi and constructing a koi ponds also requires the necessary time and expertise. In order to optimally care for your koi, the necessary preparation is required when constructing a koi pond. You will also have to take into account the fact that a koi pond must meet specific requirements with regard to material use as a pond filter and pond pump. It is even possible to heat a koi pond so that you can continue to enjoy your koi throughout the year.

Koi diseases

Koi are very strong fish. With proper care, they resist many of the parasites that are susceptible to more sensitive tropical fish species such as Trichodina, Epistylis and Ichthyophthirius multifiliis infections. The pH value of the water is important for maintaining the health of koi. Water changes help to reduce the risk of diseases and reduce stress. Two of the biggest health problems with koi carps are the koi herpes virus (KHV) and rhabdovirus carpio, which causes spring viremia of the carp (SVC). No treatment is known for both diseases.

Some koi farms in Israel use the KV3 vaccine, developed by Prof. dr. Mr. Kotler of the Hebrew University of Jerusalem and produced by Kovax, to immunize fish against KHV. Israel is currently the only country in the world that vaccinates Koi against the KHV. The vaccine is injected into the fish when they are less than a year old and is accentuated by using an ultraviolet light. The vaccine has a success rate of 90% and when immunized, the fish cannot collapse due to a KHV outbreak, nor can the immunized koi pass on KHV to other fish in a pond.

Only measures such as rapid detection, isolation and disinfection of tanks and equipment can prevent the spread of the disease and limit the loss of koi carps. In 2002, spring viraemie hit an ornamental horticulture farm in Kernersville, North Carolina, and required complete culling of the ponds and a long quarantine period. A while later some koi breeders in neighboring countries stopped importing fish for fear of infecting their own koi.