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Koi Fish: Types, Behaviors, Lifespan, Costs & More

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Koi fish are an ornamental variety of fish often associated with Japan.

These fish are known for their vivid colors and usually reside in picturesque Koi ponds, which serve as both habitat and decoration.

I’ve grown to love these beautiful fish, so in this guide, I’ll break down everything there is to know about Koi fish, including the basic information about the species and how to care for Koi.

What is a Koi Fish?

A Koi fish is a subspecies of carp from the genus Cyprinus.

The Koi fish we are familiar with today are specifically called “Nishikigoi” in Japan to differentiate from “Koi,” simply the Japanese word for carp.

What is the Purpose of a Koi Fish?

Koi fish have been considered ornamental or decorative since first being bred for their color variation.

Before this, Koi was a type of common carp raised for food.

Their purpose today is purely ornamental, as the Koi fish of today are entirely domesticated.

What is the Origin of Koi Fish?

The Koi fish we know today were first bred from common carp in Japan as early as the 1800s.

Koi fish were originally a type of carp bred as a food fish in Europe and Western Asia.

When people noticed the color variations in the subspecies of carp, they bred Koi fish for their fantastic color patterns.

Similar Alternatives to Koi Fish

If you like Koi fish but wish to add a similar species to your collection, here are some alternatives.

  • Alternative: Common Goldfish: The common goldfish shares an ancestry with the Koi fish, as both species are from the common carp to achieve color variation. Common goldfish are the second most popular outdoor pond fish, coming right after Koi fish.
  • Alternative: Fancy Goldfish: Similar to the common goldfish, the fancy goldfish is ideal for outdoor ponds. However, the fancy goldfish is more vulnerable than the common goldfish or Koi, so they must be housed alone.
  • Alternative: Golden Orfes: To the untrained eye, many may mistake Golden Orfes for Koi fish. These fish are sometimes referred to as “jumping Koi” due to their similar appearance and energetic presence.
  • Pond Sturgeon: The Pond Sturgeon is well-loved for the same reason as Koi fish, as they are unique-looking fish. These massive pond fish are large and stick to the bottom, so watching them make their way around is fascinating.

How Much Do Koi Fish Cost?

Koi fish can get quite expensive, with rare varieties costing as much as $10,000.

The average Koi fish won’t be quite that expensive, with the average price for a common variety of Koi fish costing from $30 to $50.

Rare types will cost between $70 to $100.

The most significant cost when considering Koi fish is the price of the outdoor pond and upkeep.

Koi Fish Behavior

Koi fish are friendly and typically recognize and greet their owners as they become accustomed to them.

When a Koi fish is healthy and happy, they usually allow hand-feeding and may even leap in the water.

What Do Koi Fish Do For Your Tank?

Koi fish are largely ornamental fish, so they will not contribute much to your pond other than their beauty.

Their beauty and peacefulness are their main attributes and they make a lovely addition to any outdoor pond.

Is A Koi Fish Dangerous?

Koi fish are generally peaceful, though they are known to attack and eat goldfish if introduced.

These fish are not a danger to humans, and they very rarely bite.

In addition, a Koi bite will feel like nothing more than a tickle, as the teeth of the Koi are not at the front of their mouths.

Koi Fish Lifespan

Koi fish live very long lives.

The longest-living Koi fish named Hanako lived for 226 years, with scale records proving the lifespan.

How Long Do Koi Fish Live?

Though some Koi fish have lived incredibly long lives, the average lifespan for a common variety of Koi is around 50 years.

Koi fish are typically considered a lifelong commitment due to their long lives.

How Fast Do Koi Fish Grow?

Koi fish grow quite fast, reaching lengths of 9 inches within one year.

Juvenile Koi fish are usually sold at a length of around five inches, which is about six months old.

From 6 months to one year, the Koi fish grows to 9 inches, and domestic Koi reach their near-full growth of 16 inches within two years.

How Big Can a Koi Fish Get?

Koi fish is a large species of fish, which is one of the reasons they require a large outdoor pond rather than the typical indoor aquarium.

Common Koi fish reach a length of around 16 inches and a weight of around 30 pounds.

The rare Japanese varieties of Koi fish reach lengths of around 26 inches, and their weight varies with the type.

Tank and Water Requirements

The tank and water requirements for Koi fish are very specific, as these are a large pond-variety species.

Best Tank Size for Koi Fish

Koi fish grow quite large, so they must be kept in large, outdoor ponds.

The general rule for keeping Koi is the pond should hold 300 gallons of water per Koi fish.

The minimum depth of the pond must be four feet, as Koi need to be able to stay low to the bottom of the pond for the winter months.

Best Water Parameters & Conditions for Koi Fish

As Koi fish are kept in outdoor ponds, a thorough temperature system should be implemented to ensure the Koi fish are comfortable year-round.

The ideal water temperature for Koi is between 73 and 85 degrees Fahrenheit.

The pH level of the water should stay between 6 and 9, and manual or electric water filtration should be applied to ensure the water is clear.

Do Koi Fish Need an Air Pump?

Yes, Koi fish need an air pump to circulate oxygen within the pond.

Ponds do not generate oxygen in the same way streams or rivers do.

The ideal oxygen levels for Koi fish are around eight parts per million, while the absolute minimum is six parts per million.

Best Habitat for Koi Fish

Koi fish should always be kept in an outdoor pond rather than an indoor tank.

The pond should have a minimum of four feet in depth, as Koi fish need to be able to swim low to the ground and away from the surface of the pond when necessary.

Do Koi Fish Need Live Plants?

Live plants are an excellent addition to any outdoor pond, and the Koi fish will appreciate the effort.

Live plants increase oxygen levels and serve as a potential shelter for the fish to feel more comfortable in their environment.

In addition, live plants increase the visual appeal of your outdoor pond.

Tank Mates for Koi Fish

Koi fish are generally peaceful, so there are many other pond fish with which they can cohabitate.

How Many Koi Fish Should Be Kept Together?

Koi fish prefer having at least one companion, so the minimum number of Koi fish is two.

The main concern when increasing the amount of Koi fish is the pond size, as Koi require around 300 gallons of water per Koi fish present.

What Fish Make Good Tank Mates for Koi Fish?

Here are some of the best tank mates for Koi fish:

  • Barbel
  • Barbs
  • Catfish
  • Shubunkin Goldfish
  • Golden Orfe
  • Tench
  • Pleco
  • Pond Sturgeon

All of the above fish thrive in ponds and are known to be peaceful with Koi.

Which Fish Should Koi Fish Avoid?

Small varieties of goldfish are the most important fish for Koi to avoid, as the Koi will eat any goldfish smaller than them.

Larger species, such as Shubunkin goldfish, are suitable only because they are large enough that the Koi do not consider them a meal.

Breeding and Reproduction

Breeding Koi fish is how we have so many beautiful color variations of this fish in the world, so many people wonder about breeding with this species.

Do Koi Fish Breed Easily?

Koi fish breeding is not considered easy because of the time and resources required for the process.

Koi mating seasons take place from February to May.

The main factor affecting breeding is water quality.

  • How Long Does It Take for a Koi Fish to Have Babies? Koi fish reach sexual maturity at around three years, then mate once a year every four to six years.
  • How Long is A Koi Fish Pregnant? After breeding takes place, the female Koi fish will become pregnant for four days before releasing her eggs. It is important to note that once the eggs are laid, the parents will likely eat a small number of the eggs.

How to Care for Koi Fish

Koi fish are easy to care for, as most of the care falls on creating the ideal environment.

General Care for Koi Fish

Creating the right environment for Koi fish can be an ordeal initially, but upkeep is generally easy.

Water should be maintained at a temperature of 75 to 86 degrees Fahrenheit and an oxygen level of 8 parts per million.

Koi Fish Diet and Feeding

Koi fish are omnivores, and most of their diet should come from plants and insects in their pond.

Koi fish pellet food and insect larvae can be purchased and hand-fed to the fish several times throughout the day.

Common Problems With Koi Fish

Water quality issues are the cause of most issues with Koi fish, though the species also struggle with a disease called Koi herpes virus.

A Koi infected with the herpes virus will likely pass away, though there is a concern for tank mates as other Koi will become carriers of the virus.

Frequently Asked Questions

Here are some frequently asked questions regarding Koi fish.

Are Koi fish better than goldfish?

Koi fish and goldfish share a common ancestry, as both were originally bred from the common Asian carp for their color variation.

Whether a Koi fish or goldfish is better for you likely depends on how you wish to house your fish.

Koi fish are kept in outdoor ponds, while many species of goldfish can live in tanks indoors, so the decision typically lies in which method you prefer.

Can I swim with my Koi fish?

If you happen to have a very large pond that your Koi fish are kept in, you can swim with the fish.

However, most Koi fish are kept in outdoor ponds that would not be comfortable to swim in, so the decision is yours.

Wrapping Up

Now that you’re a Koi fish expert, will you choose to bring some of these beautiful pond fish into your life?

The most important things to remember with Koi are the quality of your pond and remember to enjoy the sight of these fish.

To get an up close and personal look at Koi Fish click here.

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