5 Facts About Koi Fish

Published Sep. 29, 2022

Koi fish are an extremely popular and colorful form of the fish species Amur carp (Cyprinus rubrofuscus). These fish are commonly kept as an ornamental fish in outdoor ponds or garden water features. They have a rich history in Asian culture dating back thousands of years—but are not related to goldfish despite their similar coloration. Their bright vibrant colors and behaviors can provide a splash of color and activity to any outdoor pond.

Koi Fish Meaning

Koi is actually the informal name for this species—they are often referred to as Japanese koi or their Japanese name, Nishikigoi. Nishikigoi is known as the “swimming jewel.” In Japanese culture, koi fish are often kept since they symbolize luck, prosperity, and good fortune.

A koi fish was first displayed in Tokyo in 1914—propelling their popularity around Japan. This was also around the time selective breeding started in Niigata, Japan, which developed and spread worldwide.

Koi Fish Pond

Koi are commonly kept as pets in outdoor ponds. Ponds can be great ways to enjoy your Koi and even provide a scenic landscape to your property, since they often include elaborate rockwork and waterfalls. Koi are temperate freshwater fish that can adapt to water temperatures between 45-95 F. When keeping koi, it is recommended to keep them at a temperature between 68-75 F. A deep pond can maintain a thermocline (temperature gradient) in the water, allowing koi to experience different temperatures.

A deep pond will also make it easier for koi to stay in the pond during winter. Water can freeze anywhere between 18-24 inches deep in a pond. Ensuring your pond is deep enough will prevent your fish from freezing. During the winter, koi will go into torpor or dormancy when the water temperature reaches 45-50 F. Their bodies will shut down and will not require as much food. A pond heater can be added to increase the temperature of the water to ensure koi survive winter temperatures. Special measures can be taken if your pond freezes over during the winter. For example, creating a hole in the ice and adding an aerator can help your koi survive.

When selecting fish for your pond, remember that smaller fish will grow over time. Knowing how big your fish will become as an adult is important to determine how many fish can be kept in a pond. Generally, every inch of fish requires about 10 gallons of water. So a 100 gallon pond can have a 10 inch fish.

Prices of Koi Fish

Koi can range in price due to many factors. Typically, a small koi will run anywhere between $8 to $50. Some koi, depending on size and color, can cost over $100. The most expensive koi ever sold at auction was for 1.8 million dollars in Japan at the 2017 All Japan Koi Show.

Factors that determine the price point for koi may include:

  • Genetic lineage: Highly sought after lineages are more expensive

  • Koi variety: The most popular varieties include Kohaku, Sanke, and Showa

  • Pattern: Steps and symmetry in patterns often can increase the price of a koi

  • Size: Larger animals are more expensive

  • Origin: Imported animals are more expensive than domestically produced animals

  • Number of fish purchased: If koi are purchased in bulk the price tends to be lower. Make sure you can house all the koi you intend to purchase if they are not fully grown yet

Koi Fish Color

There are over 100 different varieties of koi that are separated into 16 groups based on Zen Nippon Airinkai (the original koi club) who oversee the breeding and judging standards of koi. Koi can be differentiated by coloration, pattern, and scalation. New varieties of koi are constantly being developed by selective breeding.

Three core colors make up many koi varieties: red (Hi), white (Shiro), and black (Sumi). Other colors that are commonly seen include yellow, orange, blue, and cream. Some fish may have a silver or gold metallic sheen to their appearance. It is common for koi to be tricolored but they can also be either single, bicolored, or multicolored.

How Long Do Koi Fish Live?

Koi, when provided with the correct environmental conditions, can live between 25-50 years on average. Reports of koi living to 100-200 years do exist—the oldest koi ever documented lived to be 226 years old. Water quality, pond conditions, nutrition, and preventative health care can help improve the longevity of a koi’s lifespan. There are many commercial koi fish foods that are available to pet parents, and can be used exclusively to feed koi and provide complete nutrition. Overfeeding is a common concern that can lead to health issues.

Providing appropriate vet care can help improve the lifespan of any koi. Not all veterinarians will treat fish, so be sure find a veterinarian who specializes in your pet. Organizations such as the American Association of Fish Veterinarians (AAFV) and Find a Fish Vet function can help assist in finding a vet that has experience treating koi.

Featured Image: iStock.com/Appfind

Sean Perry, DVM


Sean Perry, DVM


Dr. Sean Perry completed his undergraduate degree at the University of California, Santa Cruz, earning a Bachelor of Science in...

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