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22 Amazing Koi Fish Facts: Characteristics, Origins & More

Rachael Gerkensmeyer

By Rachael Gerkensmeyer

beautiful koi fish

Koi are a common variety of carp, a particularly beautiful ornamental version. The word Koi is derived from the word “carp” in Japanese. It is believed that Koi fish were caught and then bred by rice farmers on their properties in the 19th century1. They were also bred in Europe and China. These colorful fish can grow up to a whopping 3 feet in length when fully grown! If you are interested in learning more about these fish, check out these 22 Koi facts!

The 22 Facts About Koi Fish

1. There Are More Than 100 Types of Koi

With more than 100 varieties of Koi in existence, you may wonder how anyone can tell them apart from one another2. Each Koi variety has its own unique coloring, pattern, and/or size. The different varieties are created through mindful breeding practices.

koi fish pond
Image Credit: Yedidia Klein, Pixabay

2. These Are Hardy, Tough Fish

Koi fish have a reputation for being hardy and tough, as they seem to readily resist parasites and illnesses that tend to create havoc for other types of fish. This makes it easy for farmers to breed and manage them in ponds. Koi can live in large groups, and if the water is maintained, there is no serious risk of vulnerability.

3. Japanese Koi Tend to Live Longer Than Koi From Other Parts of the World

Outside of Japan, Koi fish have a life expectancy of about 15 years. However, inside Japan, these fish are known to commonly live for an amazing 40 years. It’s even said that some Koi live up to 100 years old. Although such a lifespan is super rare, one Koi fish from Higashi-Shirakawa Japan was documented as living to an astounding 226 years, making them the oldest Koi fish on the planet.

4. These Fish Are Known to Eat Almost Anything

Koi fish are omnivores and are considered opportunistic when it comes to eating, as they will try to eat almost anything that they can get their mouths around, even other fish. However, it seems that their favorite foods are greens, watermelon, bananas, and peas.

koi fish eating pellets
Image Credit: Russell De Boer, Pixabay

5. Females Typically Lay Thousands of Eggs During the Breeding Season

During the breeding season, males encourage the females to lay eggs for them to fertilize. The females will lay clutches of eggs that can number in the hundreds or even thousands. The larger the female is, the more eggs she can lay at a given time. These fish can lay up to 100,000 eggs during a spawning season3. The eggs attach to whatever they come into contact with once laid, and they are typically fertilized by a male shortly afterward.

6. Koi Eggs Typically Hatch Within 2 to 5 Days

Once fertilized, the average Koi egg hatches in between 2 and 5 days, so the process happens quickly. The hatchlings are called “fry.” After her eggs hatch, a mother goes on with her business and starts producing more eggs in her body in anticipation of the next breeding/spawning season.

7. Unfortunately, Many Eggs Don’t Make It to Fruition

After a Koi fish lays her eggs, they instantly become susceptible to destruction. Many factors play a role in the ability of an egg to come to fruition and actually hatch. One of the biggest threats that Koi fish face is the prospect of being eaten by other Koi fish in the area.

8. These Fish Are Thought to Be Able to Recognize Faces

Koi fish have long-term memories like humans do, and they can remember the faces of people who come to visit them. They can even learn their own name and come when you call them as a dog might do.

Image Credit: Jerawat Supajirakit, Shutterstock

9. Koi Were Developed in Captivity

Koi fish were created through captive breeding, so they can’t be found in the wild unless they are released there from captivity. Koi fish are too valuable for most people to do this, wild though, so finding them like you would other wild fish is extremely rare.

10. These Fish Are Considered Symbols of Good Luck

In Japan, Koi fish are considered tokens of good luck. Their energy is thought of as flowing and at ease. In Feng Shui, it is believed that Koi fish represent fortune, food luck, and life benefits in general. In short, these fish represent advancement and abundance for many people, especially in Japanese culture.

11. One Type of Koi Has “Butterfly” Fins

Aptly named the Butterfly Koi, this variety of Koi has, long, flowing fins that resemble the wings of a butterfly because of how they move, which is gracefully and mindfully. Butterfly Koi fish are also known as Longfin Koi and Dragon Carp. They are typically bred and sold around the world.

Butterfly Koi Fish_fivespots_shutterstock
Image Credit: fivespots, Shutterstock

12. They Were Originally a Japanese Food Source

Originally, carp were brought to Japan as a source of food, which is how they ended up being bred with other fish until the Koi fish was created. Eventually, they were developed into beautifully colorful fish that were more valuable as ornamental pets than human food.

13. Speckled Carp Were the Inspiration for Koi

Farmers noticed that a few carp that they were breeding had white patches on their bodies and decided to try breeding those fish with others like them. This resulted in the beginning of the breeding of the bright colorful fish that we call Koi today. As time went on, different color and pattern variations were produced, and now there are several dozens of varieties of Koi fish.

14. The Koi Became Notable Due to a Japanese Emperor

In 1920, Emperor Hirohito received a Koi fish as a gift, which made the fish notable among “commoners.” Suddenly, ponds filled with colorful Koi fish became popular hotspots for Japanese residents and others around the world. Hirohito placed his Koi fish in the Tokyo Imperial Palace Pond and let it spawn until the pond was so filled with Koi that the fish had to be transferred to other ponds throughout the country.

15. Koi Are Distant Cousins of Goldfish

Although Koi fish are derived from carp, they are also distant cousins of the Goldfish, which are descendants of carp themselves! These are two distinct species, but they have a few things in common. Pay attention to how both types of fish move flowingly and knowingly in the water, for example.

Image Credit: R: kaori, Pixabay | L: jggrz, Pixabay

16. The Largest Koi in the World Weighs More Than 90 Pounds

Weighing in at an impressive 91 pounds, a Koi fish named Big Girl is a staggering 4 feet long. Although a Koi, this fish is orange in color and does not possess any of the impressive colors that the typical Koi does. In fact, Big Girl looks like a giant Goldfish!

17. They Thrive in Social Settings

Koi fish are like humans in that they thrive in interactions rather than being isolated from others. This is why so many Koi fish can live peacefully in a pond together. They don’t mind interacting and learning each other’s features so they can tell each other apart.

18. Koi Fish Are Trainable

Koi fish have long-term memory and are quite smart. These traits together result in the ability of Koi fish to be trained by their human companions. They can learn how to do things like eat from the hand and interact with friendly cats. All Koi are trainable, but their trainability depends on their environment and how much time and effort their owners put into training them.

19. These Are Freshwater Fish

Many people believe that Koi fish live in saltwater, but that is not the case. These fish thrive in freshwater, which is why they do so well in ponds and even above-ground swimming pools. They do not need plants and greenery to survive, but they do in order to thrive. This is why it’s not recommended to breed them in swimming pools, as these are not outfitted like aquariums are. These fish deserve a diverse and interactive environment to live in.

white koi in between two black koi in the water
Image By: es3n, Shutterstock

20. They May Outlive Their Owners

Anyone who is middle-aged and acquires one or more young Koi fish should consider who would be the godparents of the fish because chances are that the fish will outlive them. It is important to establish who will take over their care to ensure their survival and that of their offspring.

21. Koi Fish in Japan Are Sometimes Family Heirlooms

Some families in Japan think of the Koi fish in their backyard ponds as heirlooms, so they pass the fish down to their younger family members as an inheritance. People who receive Koi fish as heirlooms feel a duty to care for the fish as well as the original owners and may pass them on themselves when they get older.

22. Koi Fish Is Not Typically Cheap to Acquire

While you may be able to find “backyard” Koi fish for about $10 a piece, most of these fish can cost thousands of dollars. Some Koi fish can cost upward of $20,000 due to their large size, hardiness, and good health. Size, shape, and coloring almost always relate to the pricing.

Final Thoughts

There are many varieties of Koi fish in existence, but one thing that they all have in common is their ancestor: the carp. They are also distant cousins of the Goldfish, and they love to spend time in social settings. These fish can be wonderful interactive pets, and in any case, they are amazing centerpieces in pond settings.

Featured Image Credit: IamSuperPear, Shutterstock

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