Koi Fish (Nishikigoi)


Common Name(s)Koi, Fancy Carp, Nishikigoi (錦鯉)
Scientific NameCyprinus carpio
Cyprinus rubrofuscus
OriginCentral Europe, Eastern Asia, Japan
Temperature Range59-77°F
Water ParameterspH 7.5-8.0
Adult Size15-30 inches
DietOmnivores feeder. Feed pellet, insects, shrimp, rice peas, watermelon.

Koi Fish Facts

  • Koi fish can regularly live to be 70 years or more, making them lifelong pets.
  • Koi fish are very intelligent. They can be trained to take food from the hands of a person and can recognize the person who feeds them regularly.
  • There are over 80 different variations of Nishikigoi.
Koi Fish (Scientific Name: Cyprinus rubrofuscus)
Koi Fish (Cyprinus rubrofuscus)

Scientific Name of Koi Fish

The generally accepted scientific name of koi fish is Cyprinus carpio. However, some studies have suggested that the parent species of koi fish may be Cyprinus rubrofuscus. While more research may be required to clarify the exact species and scientific name, this is not an easy task. Modern koi fish is often bred extensively. In addition, koi fish that are considered to be true ‘Nishikigoi’ may very well be hybrids of multiple species. Since the term ‘koi’ and ‘Nishikigoi’ is not a term that is tied a single species by definition, the scientific name of koi fish can be either Cyprinus carpio or Cyprinus rubrofuscus, or both.

For example, Shusui is a koi variety that is recognized by the Zen Nippon Airinkai. Shusui was developed by cross-breeding Japanese Asagi Sanshoku and Doitsu-goi (German Carp). Therefore, it is very likely that modern Shusui koi is a hybrid specimen of both Cyprinus carpio and Cyprinus rubrofuscus. The fish was bred by Kichigoro Akiyama, a teacher at what is now the Tokyo Fisheries College. This occurred after the German Carp was first imported to Japan in 1904.

Kawarimono is another koi variety that is recognized by the Zen Nippon Airinkai. In fact, Kawarimono is more of a category of koi, rather than a single variety. Many koi varieties that do not hold a stand-alone place in koi show entries are grouped into this category. Koi in this category may very well have more than one scientific names associated with it.

Koi Fish Overview

The word “Koi” is a Japanese word meaning “carp”. These fish were originally raised for food by rice farmers. However, when they noticed that some of the fish had developed color mutations, they decided to keep the fish and continue breeding them. The word “Nishikigoi” in Japanese refers to these carp that have colors and patches and are raised as ornamental fish. In Japan, it symbolizes wealth, love, success and good fortune.

Koi is a cold-water fish and originate in Central Europe and East Asia. They are hardy and highly adaptable. Likewise, the domesticated Nishikigoi can be acclimated to various climates and water conditions.  Koi fish and Goldfish have the same ancestor, the carp. They have similarities with some varieties of Goldfish such as the Common Goldfish and Comet Goldfish. They can have similar body shape and color. This makes it difficult to tell the difference between the two as juvenile or fry. One obvious feature that distinguishes the Goldfish and Koi fish is the presence of prominent barbels on the lips.

Due to their bright colors, they are easily noticed by different fish devouring predators such as Herons, Kingfishers, raccoons, cats, and hedgehogs. To mitigate this, Koi fish breeders often make use of ponds that are too deep for herons and build barriers around the koi ponds that are too high for the mammals to cross over. Koi fish are also sensitive to the sun. They can easily get sunburned, so providing adequate shade is important. Koi fish is docile in nature, and can only be raised with breeds of fish that are also docile. Under ideal conditions of proper diet, oxygen, and adequate temperature, koi can grow 2 cm per month. The domestic Koi are capable of growing up to approximately 15 inches long while the Japanese Koi can grow up to approximately 30 inches in length. 

Koi fish are omnivous and they are not picky eaters. They will readily consume a wide variety of treats which includes cooked rice, orange slices, grapes, watermelon, garlic, broccoli, and lettuce. They will also graze on insects and snails in the pond. While treats are readily accepted, commercial koi food is a convenient way to ensure a balanced nutritional diet. There is a wide selection of off-the-shelf feeds available on the market today. For example, there are koi feed that are designed to enlarge the body or feed specifically designed to bring out the beautiful colors. Hikari manufactures some of the best koi food on the market today.

Koi’s mouth part has been naturally configured for bottom-feeding at the pond. While they do graze the bottom of the pond regularly, they have no issues feeding on floating food. This allows them to come to the surface to feed. Feeding time should also be used to check for the presence of parasites and ulcers on the fish. Feeding is not recommended when the water temperature is below 41°F. Koi fish do not have a stomach. The food that they eat go directly from the esophagus to the bowel. This means that they cannot keep the food in their system for a very long time. Therefore, it is best to give small amounts of food frequently, rather than giving a large amount of food all at once. Small feedings of 2 to 4 times a day is recommended. An automatic pond feeder can easily make this possible. Check out the Koi Feeding Guide for more details.

Koi fish have a long lifespan and they can live for many decades, while some live for over a century. The oldest koi recorded in history is the legendary koi named Hanako that live from 1751 to 1977, living a total of 226 years. Similarly to the rings on the bark of an evergreen tree, the microscopic growth marks on the scale of the Koi fish can be used to tell the age of the Koi fish.

Due to its beauty and wide-spread popularity, the koi fish is now bred in many countries. They are being enjoyed by many enthusiasts from all over the world.

Nishikigoi and Koi Variety

Koi fish can display beautiful striking colors with many different patterns. As breeding techniques have advanced, many variation of the Koi fish have been developed; common colors range from blue, black, red, white, yellow, and cream depending on their variety. There are over 80 different variations of Nishikigoi, and these varieties can be distinguished by their color, escalation and body pattern. To this day, different varieties of Koi fish are still being developed. Currently, the International Nishikigoi Promotion Center specifies 26 fixed varieties of Nishikigoi. This includes Kohaku, the oldest and most well known variety of Nishikigoi.

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