A group of koi fish swimming.
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Cyprinus carpio
  • CLASS: Actinopterygii (Ray-finned fishes)
  • ORDER: Cypriniformes
  • FAMILY: Cyprinidae
  • GENUS: Cyprinus
  • SPECIES: carpio
  • SUBSPECIES: C. carpio haematopterus



Koi are ornamental varieties of domesticated common carp that originated in Japan. They are kept for decorative purposes in outdoor ponds with very clean, oxygenated water and plenty of shade (the fish are susceptible to sunburn!). There are over 100 varieties of koi, which can be red, white, black, yellow, brown, gray, and green, and many combinations thereof. Koi resemble oversized goldfish and, in fact, koi and goldfish are both types of carp. 

In the 1600s, Chinese farmed carp in rice paddies as a food source, a practice that traveled to Japan. The Japanese noticed odd color variations in some of the carp and bred them, creating a rainbow spectrum of koi species. Koi were prized by royalty; by the 1900s, koi were being bred in Europe, England, and the US. By the 1960s, keeping koi as a hobby had caught on around the world. Today, they are kept as pets on 6 out of 7 continents. 

Koi are culturally significant and represent love and friendship in Japan. Some koi can live over 200 years, so they are passed down from generation to generation and considered a family heirloom in Japan. Varieties of koi are distinguished by their coloration and scale pattern. They are social, "schooling" fish.

According to a popular feng shui website, the Japanese name and symbolism for some different koi include:

  • Kohaku: white body with red spots (symbolizes success in your career)
  • Kumonryu: unique type of koi, either solid black or white body with black spots; its pattern changes as the koi grows (symbolizes life changes and transformations)
  • Ogon: silver-colored body (symbolizes success in business, wealth)
  • Kuchibeni: white-and-red patterned fish referred to as the "lipstick" koi, since the red color around its mouth resembles puckered lips (symbolizes love and long-lasting relationships)
  • Yamabuki: gold-colored body; this is a popular restaurant name (symbolizes riches and wealth).


These domesticated carp can live in aquariums, but their true value is in outdoor ponds and water gardens. They are mostly vegetarians—rice and corn are among koi's favorite foods—but they will also eat live shrimp and even their own young, called "fry," before the little fish's coloration comes in. To ensure healthy, long-lived koi, it is best to give them standard koi food, which is at least 30 percent protein. 

Koi can be trained to eat from a person's hand.


Koi are docile, social fish. Other fish species can be added to their pond if they are not aggressive. 

These fish reproduce through spawning, usually in early summer, where a female lays a vast number of eggs and at least one male fertilizes them.


Ten colorful koi glide around the Zoo's Terrace Lagoon in a 18,500-gallon pond, along with tiny mosquito fish and a bluegill or two. The pond as been around for decades, initially serving as a bird pool. In the 1990s, a filtration system was added to support the koi. 

The system operates 24/7, and the water is disinfected with ozone gas to remove contaminants (chlorine is not compatible with fish). The pond is vacuumed once a week. Keeping the water clean is critical for healthy and happy koi!


Koi breed well in captivity and are prized fish among collectors. They are not endangered. 

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Typically 25 to 35 years if cared for properly; some can live up to 200 years


Koi spawn with females laying many eggs and one or more males fertilizing them

Young "fry" face many challenges, including parasites and hungry adults who may eat them before their coloration comes in 


Length: About 3 feet (91 centimeters) maximum

Weight: About 35 pounds (16 kilograms), on average


Koi are illegal in the state of Maine, but legal in the other 49 US states.

These colorful fish can be worth thousands of dollars.

Without a good filtration system in their pond, koi would poison themselves, as they excrete ammonia.

A fish named Hanoko was the oldest living koi. He lived to be 226 years old. Hanoko was born in Japan in 1751, five years BEFORE classical genius Mozart was born. Hanoko died on July 17, 1977.

Koi, like goldfish, are carp.


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