Fun facts about koi

By David Brown

Have you ever been in a beautiful garden with a pond? A waterfall gently tumbles into the pond — what’s that moving below the clear water?  

It’s a multicolored fish with orange, white, and black splotches, like someone painted it. It’s a koi!

Koi are prized by gardeners, fish collectors, and people who appreciate beauty. These fish have a long and interesting history. Where did they come from and why are they here?

Let’s explore the history and mystery of koi.

1. Made in Japan

The koi story starts in Japan. Koi are domesticated fish. They were bred by people from wild fish, just like dogs were bred from wolves. Koi are domesticated carp. 

The wild ancestors of koi are called Amur carp. These carp came to Japan from mainland East Asia at some unknown time in the distant past.

2. Colorful carp carnival

In Japan, people have been keeping carp in captivity for thousands of years. At first, carp were kept for food. But people noticed that the Amur carp had three different color mutations: black, white, and red. They wondered what other colors were possible. 

Starting in the 1800s, Japanese carp farmers experimented with breeding carp to create varieties with vibrant colors and beautiful patterns. Over time, many of these colorful varieties were developed into the carp breeds that are now known as koi.

3. Oh boy, koi!

There are now more than 100 varieties of koi in the world. Some breeds are very expensive. In 2018, a single koi in China sold for TWO MILLION DOLLARS!

Koi are regarded as beautiful parts of gardens in Japan and around the world.

4. Goldfish cousins

Sometimes koi get mistaken for goldfish. While it’s true that both koi and goldfish are domesticated carp, they come from different ancestors. Goldfish come from a carp species called crucian carp, and were domesticated in China. 

A key difference is that koi grow much larger than goldfish, and live much longer. Adult koi can grow to 60–90 centimeters (24-36 inches) long and weigh 9-16 kilograms (20-35 pounds). Goldfish are typically 5-15 centimeters (2-6 inches) long and weigh less than a half a kilogram (1 pound). In good care, a koi can live 70 years or longer. Did you know? The oldest recorded koi was more than 200 years old! By comparison, goldfish live around five to 10 years in good care.

5. Koi belong with people

Koi were bred to be admired in human-built spaces like gardens and fishponds, not in the wild. However, there are many examples of koi being released into the wild when their owners no longer want to care for them. This is not good because the koi can become invasive species and hurt native wild fish by eating most of their food.