Koi Fish – A Complete Guide (Care, Diet, Facts)

Raising Koi fish is a rewarding way to add variety and beauty to your space.  They can provide a dignified elegance and companionship for decades.  They can be used as the centerpiece of your landscape or grace a quiet corner of the yard.

Keeping Koi is an affordable entry level hobby.  While Koi prices are generally low some have sold for hundreds of thousands of dollars.  Don’t worry though! You can buy some species for less than the cost of lunch.  And who knows- maybe you will decide to become a Koi breeder.

Koi are available all over the world in several interesting colors and species.  They live long lives with little upkeep.  Several Koi have lived to be over 100 years old!  Armed with the right information, maintaining a Koi pond can be a simple but satisfying task.


History of Koi Fish

Believed to have started as early as the 4th Century in China, raising Koi fish has blossomed into a hobby for people around the world.

Initially found in China, Koi were brought to Japan as gifts.  It took centuries of selective breeding for these original species to become the iconic fish we see today.  Currently, Koi farmers have identified 100-200 varieties.

Modern Koi are a result of 19th Century breeding in Japan.  The Koi lived in basins above rice fields.  The Koi droppings in the basins provided highly fertilized water for the rice.

From these basins, rice farmers would capture the most colorful carp and breed them.  Fish that didn’t have qualities that the farmers wanted to replicate were used as food.

The original fish were Carp.  “Koi” is the Japanese name for Carp.  Interestingly, “Koi” has the same pronunciation as the Japanese word for “love” or “fondness”.  This has turned out to be a very appropriate coincidence.

They may also be referred to as “Nishikigoi”.  This translates to “swimming jewel”.  Ancient Japanese nobility latched on to the idea of having living “jewelry”.  Koi became a symbol of wealth, ambition, and power.

Japanese nobility began keeping them in small ponds.  The fish were fed a wheat flour-based food called “Fu”.  Fu is a nutrient rich food that was eaten by everyone from monks to aristocracy.  It was a national food staple during a time when protein was scarce.

The nobility appreciated how the fish ate the food calmly, never acting in the typical aggressive manner of most fish.  This trait became an example of how to act for many Japanese people.  The behaviors of the Koi spread throughout the entire culture.

Interesting Koi Facts

Likely the most famous Koi was born in 1751.  Hanako lived for 226 years, through multiple owners.  Her final owner had her scales analyzed by scientists who were able to count the rings of growth.  This allowed them to determine her remarkable age.

Several Koi sold for enormous sums to Japanese companies in the 1980s.  Having remained a status symbol for the wealthy, these Koi sold for upwards of 1 million dollars.

Ancient art depicted Koi fish on pottery and plates.  These were painted from a top-down perspective.  To this day, live Koi are judged based on their appearance from the top down.

In 2014, a flood washed out Romsey World of Water in Hampshire, England.  A Koi traveled from its pond at the park for seven miles to a puddle near a pub.  The water receded, leaving it trapped.  It lived in the puddle for two months before being discovered and returned to the World of Water.

Gosanke Koi have won every competition at the All Japan Koi Show since it started in 1966.  The only time this variety has not won the competition is when an outbreak of Koi Herpes caused the competition to be canceled in 2003.  An earthquake in 2004 caused another cancellation.  Other than that, Gosanke Koi has remained the champion.

Common Types of Koi Fish

The most common colors of Koi include white, black, red, yellow, blue, and cream.  However, almost every color is represented by some breed of Koi.

A Koi’s colors will develop as it ages.  Males will reach their full coloration at a much younger age than females.  Regardless, the pattern and colors will be mostly established by the time the Koi is aged three years.  Despite this, a Koi’s pattern and shade will change throughout its life.

Breeders are adding new varieties through specialized farming.  The most popular types can be found in some combination of the below.

Gosanke Koi are the most prevalent.  Due to its popularity and staying power it is often considered the quintessential Koi.  “Gosanke” is used in Japanese to represent the biggest three things in a category.  For Koi, the big three are Kohaku, Sanke, and Showa:

  • Kohaku- Kohaku are a white fish with a red pattern on top. The red patches are large and can cover most of the fish.
  • Sanke- Sanke Koi were bred from kohaku. Their large red patches are sprinkled with black dots.  All of this is on a base color of white.
  • Showa- Whereas, Kohaku and Sanke fish are considered white with red and black spots, the Showa is black with red and white spots. The pattern can extend to include the fish’s head unlike the other two.

One of the oldest breeds of Koi are the Chagoi.  These fish are very similar to wild carp in appearance.  Their coloration is indicated in the name.  “Cha” is from the Japanese word “ocha”, meaning tea.  They are known for their ability to be tamed and eagerness to be fed by hand.

Koi experts don’t just rely on color to judge the quality of a fish.  Body shape and skin quality are also considered.

The body should be uniform with a round nose.  It should be elliptical in shape- not too fat and not too thin.  Bumps or obvious deformities lower the quality.  Skin should appear bright and the scales should blend.  The fins should match in size and color.

Ideal Koi Fish Habitats

Carp in the wild are a highly tolerant species.  They have made a home on every continent except Antarctica.  They prefer large bodies of water.  Typically, this water is slow moving or standing.  The bottom is made up of decomposed vegetation; essentially mud.

They prefer water temperatures from just above freezing to 95 degrees.  Ideal temperatures are between 73-86 degrees.  Carp can live in water that is covered with ice if there is some unfrozen water at the bottom.

They won’t begin to spawn unless the water temperature reaches around 64 degrees.  They need plant life to lay the eggs on.

Ideally, their natural habitat receives sun all day long.  Trees and bushes that hang out over the water give the fish a place to hide and cool off from the sun.

It is essential to replicate these characteristics when designing a pond for pet Koi.  Small Koi need around 50 gallons of water, but a full-grown Koi may need 500-1000 gallons of water per fish to thrive.  For example, a pond that is six feet by eight feet and four feet deep can house five full grown Koi.

The deepest part of the pond should be at least four feet deep and large enough to accommodate all your fish.  This allows them to survive during the winter if freezing is an issue.  They can enter a type of hibernation for short periods of time if they don’t have access to the water surface.

The pond should be insulated from ground water and leaking by adding a liner.  All rocks and sharp objects should be removed before the liner goes down.  A layer of sediment can be added on top of the liner to replicate the decomposed vegetation found in the wild.

Pond friendly plants should be added that provide shade and compostable material.  This will help maintain the sediment layer.  A pond partially shaded by trees or bushes will help the fish keep a comfortable temperature on hot days.

Typical Koi Fish Behavior

Just like most other creatures, Koi will display behaviors that give clues to how they are feeling.  Understanding these cues can help you adjust your care to keep them as happy and healthy as possible.

Generally, Koi are very friendly.  Familiarity with their environment helps keep them friendly.  If you have changed the layout of the pond or added a new fish, expect a period of adjustment.

Keeping a regular feeding schedule will also help them stay friendly.  Stay by the pond while they feed.  This will help them learn to recognize you.

A stressed Koi will show signs as well.  Changing up their environment too quickly can cause this.  Pollution in the water or a nearby predator can cause behavior changes.  A stressed Koi may begin rubbing itself on the edges of the pond causing ragged fins.

Stressed fish will eventually become sick.  Illness can spread very quickly in small ponds so it’s important to recognize signs early.  These sicknesses will have different symptoms but there are some common signs to look for.

Rapid or unusually slow swimming may be a symptom of illness.  Another sign of sickness is uncoordinated swimming patterns.  Koi are known for their gracefulness so a sudden lack of coordination should indicate a problem.

An easy behavior to notice is jumping.  Koi will jump in order to get oxygen.  Lots of jumping indicates a lack of oxygenated water.  Occasional jumping isn’t something to worry about.  If all the fish are jumping often there may be a problem.

Check your filter for a clog.  If you don’t use a filter, make sure the surface of the pond isn’t covered in debris like leaves or algae.  Pond plants or a waterfall feature can also help add oxygen.

Koi Fish Care

Koi care starts with a carefully considered pond.  Ideally, it will contain a filter, pump, and sterilizer.  These items will keep water flowing and clean.  The pond should have access to plenty of sun and shade.

Pollutants are a widespread Koi pond issue.  Too much fish waste is a common cause of this.  Run off from fertilized gardens can affect water quality, too.  Believe it or not, acids in the rain can change the Ph balance enough to degrade fish health.  These issues can be identified early by frequent checks of your water.

Eager Koi owners can often overfeed their fish.  This hurts your pond in two ways.  One, the fish become overfed and unhealthy.  Two, the excess food rots and pollutes the water.

If water checks are showing high ammonia and nitrite levels, consider cutting back on the food.  Overfeeding can manifest itself into parasites, fin rot, and other health issues.

If you have decided to add new Koi to your pond be aware that the larger fish are happy to eat smaller fish.  It is recommended that smaller Koi are raised in a tank in a separate location.

Young Koi should be raised in an aquarium with around 30 gallons of water.  It should be kept out of direct sunlight.  New fish should be kept separate from the rest for a couple weeks to make sure they aren’t going to infect them with an undiscovered illness.

When it’s time for the new fish to join the community use a net to transfer them.  It is important not to just dump the aquarium water into the pond with the fish.  Experts recommend not adding more than three fish at a time.

Feeding Your Koi Fish

Luckily, Koi Fish are not picky eaters.  The simplest food they will eat is pre-packaged Koi pellets.  These come in a wide variety of types and sizes.  Ranging from small cans to fifty-pound bags, it is always cheaper to buy wholesale.

Koi will also eat just about anything else.  Bugs and other naturally occurring creatures in your pond are on the menu.  Plankton and pond vegetation will be consumed.  Feel free to throw in vegetables and other items you may have in your refrigerator.

Koi should be fed once a day.  Try to put enough food in the pond for them to eat for five minutes.  If food is remaining after five minutes of feeding, lower the amount.  Try to remove excess food to limit polluting the water.

Koi Pond Mates

Many different creatures can share a pond with Koi.  There are some common characteristics that they need to share with the Koi to keep a happy pond.

Your Koi pond will probably reach colder temperatures than a tank would.  Keep this in mind when looking at potential pond mates.  A tropical fish that would happily live in a tank with Koi would probably have a bad time in an outdoor pond.

Koi generate a lot of waste.  This will only increase as they grow larger.  Keep this in mind as you think about adding additional animals.

Try to find fish that will grow at the same pace as the Koi.  If you dump a school of smaller fish in the Koi pond, they may think its feeding time.

With these things considered, freshwater sharks are a good choice.  Specifically, the Chinese Hi Fin Banded Shark can grow up to three feet.  They are used to cold water and like to hang out on the bottom of a pond.  These fish can also help process waste at the bottom.

Trapdoor snails are a hardy species that enjoy colder waters.  They will help reduce uneaten food and algae.  They can be behind the scenes keeping your waters clean and clear.

Finally, Goldfish can complement your Koi.  They may be less visible in deep ponds.  A group of less decorative goldfish can enhance the patterns of you Koi as they meander through the pond.

Breeding Your Own Koi Fish

Interested in breeding Koi in your pond?  You can do it!  It’s important to understand what the ideal conditions should be in order to encourage breeding.  Like designing the pond, look to the Koi’s natural habitat for guidance.

Koi aren’t sexually mature until three years of age.  This means they should be about ten inches long.  It can be less obvious what the sex of the Koi are.  It can be made simple if you know what you’re looking for.

White markings on the tips of the fins identify male Koi during mating season.  Males will also be seen chasing the female fish during this period.  This will look more aggressive than their typical activity.

Identify the attributes of the Koi you want to breed.  Find male and female fish that have those characteristics.  Remove fish from the pond that you aren’t trying to breed, or you may end up with unwanted Koi.

Koi breed at the end of spring or beginning of summer.  The warmer water is a sign to the fish that it’s safe to look for a partner.  During this time, increase the amount of food you provide them.  This should include higher nutrient foods.

You can place a fry mat in the pond.  A baby fish is known as a fry.  A fry mat is a sticky pad that can hold the fish eggs.  When the fish have bred you will see a froth appear on the water surface and eggs on the mat.

It may take days or weeks for the fish to mate.  Different variables in the environment may affect this.  Some breeders think that things like storms, full moons, or significant temperature changes can trigger breeding.

If you are trying to sell the baby Koi, it is important that you remove the parents after the eggs have been laid.  Koi can lay up to a million eggs and many of these eggs end up eaten by the parents if they are left with them.

The fry should hatch in about ten days.  They will eat powdered food for around four weeks.  The feeding pellets can be ground down for this purpose.  Feeding sessions should last about five minutes four times a day.

Koi that don’t meet the standards you are looking for should be identified once they have begun to develop patterns.  These unnecessary fish are often culled in a humane manner.  However, these unwanted Koi make great gifts for friends and family.

Once the babies reach about three inches it is safe to reintroduce the parents.  This usually takes about three months.


The Japanese recognized the unique tranquility a well-kept Koi pond could provide.  The Koi’s natural elegance and friendly demeanor became a symbol of peace and a behavior to strive for.  This has now been recognized all over the globe.

The ability to bring those qualities to your own backyard is surprisingly simple.  If you are looking for a satisfying endeavor and companionship for decades to come, there are few projects as gratifying as a Koi pond.

Leave a Comment