Koi fish are colorful, ornamental versions of the common carp. Modern Japanese koi are believed to date back to early 19th-century Japan where wild, colorful carp were caught, kept and bred by rice farmers. The word “koi” comes from the Japanese word for “carp.”

Physical Description

Koi fish are a colorful, ornamental versions of the common carp. Though carp domestication is believed to have begun in China as far back as the 4th century, modern Japanese koi are believed to date back to early 19th-century Japan where wild, colorful carp were caught, kept and bred by rice farmers. There are now dozens of different color varieties of koi.


Koi can grow up to 3 feet (90 centimeter) in length.

Native Habitat

Wild koi are native to the fresh bodies of water around the Black, Caspian and Aral Seas. Domesticated in the 19th century, carp have now been introduced throughout the world.


Koi have an average lifespan of 40 years. It is believed that the oldest-known koi lived to be nearly 230 years old; the age was determined by testing the fish's scales, which produce growth rings much like a tree.

Food/Eating Habits

Koi are omnivorous feeders who will eat food found at all depths of water.

The Japanese koi at the Kids' Farm are fed a floating pellet, though they will also eat aquatic insects, algae and plants.

Reproduction and Development

Koi will migrate significant distances to reach their preferred spawning grounds — flooded meadows and stagnant marshy areas. The breeding season is in the spring, around May or June. Females reproduce for the first time when they are between 4 and 6 years old, males when they are between 3 and 5 years old.

Once they reach sexual maturity, they will breed every year. They attach their sticky eggs to water plants or any object submerged in the water. The young hatch as larvae and stay in warm, shallow flooded areas until they are large enough to brave more open waterways.

Conservation Efforts

Koi have been introduced all over the world, and they are farm-raised in large numbers for food, for ornamentation and for sport fishing. Wild populations are now at risk from hybridization with released or introduced domestic stock. They are also threatened by river control — wild carp need flooded areas in order to reproduce.

Help this Species

  • Reduce, reuse and recycle — in that order! Cut back on single-use goods, and find creative ways to reuse products at the end of their life cycle. Choose recycling over trash when possible.
  • Choose your pets wisely, and do your research before bringing an animal home. Exotic animals don’t always make great pets. Many require special care and live for a long time. Tropical reptiles and small mammals are often traded internationally and may be victims of the illegal pet trade. Never release animals that have been kept as pets into the wild.
  • Protect local waterways by using fewer pesticides when caring for your garden or lawn. Using fertilizers sparingly, keeping storm drains free of litter and picking up after your pet can also improve watershed health.

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