A backyard pond filled with colorful and graceful koi fish can bring a calm and beautiful feel to your outdoor space. These gentle fish move smoothly through the water, creating a peaceful scene. While koi fish are strong and can live a long time, they do have special care needs. This guide explains everything you need to know to help your koi live a long, healthy life.

About Koi Fish

Koi fish are popular ornamental fish that many people in Southeast Asia have admired for centuries. They are friendly, enjoy being around people, and can grow as large as 3 feet. The practice of raising koi fish started long ago in China and Japan and has become a respected tradition. Today, people around the world enjoy keeping koi, and it has become a popular part of outdoor fishkeeping. Although koi are related to common carp, they are different from goldfish. One easy way to tell them apart is that koi have small whisker-like feelers called barbs near their mouths. These help them find food in the mud. Koi are also known for living a long time—usually between 25 and 35 years—but some have even lived up to 70 years.

How Much Do Koi Fish Cost?

The price of a koi fish can vary. You might pay as little as $10 or as much as $100, depending on the size, breed, and color pattern. Some rare types can be extremely expensive. One koi fish even sold for $1.8 million after winning a major competition in Japan in 2017. While you don’t need to spend that much, it’s important to know that caring for koi fish can be costly. Building a pond that suits their needs may cost up to $2,000. Also, because koi like to live in groups, you will need more than one, which adds to the cost. Before buying koi fish, it’s a good idea to get advice from well-known websites, professional breeders, or pet stores that specialize in fish.

Behavior and Personality

Koi fish are calm and friendly. They get along well with other koi and with people. With time and patience, you can even train them to eat from your hand and let you gently touch them.

What Koi Fish Look Like and Their Different Types

Koi fish are known for their beautiful colors and patterns. No two koi look exactly the same. There are three main color types: Single-colored Koi These koi come in one solid color—such as white, red, yellow, or orange. Some rare types can be very expensive. Two-colored Koi These have two main colors, like red and white, orange and white, or black and white. These are among the most common types of koi. Three-colored Koi These have three colors. Some have clear patterns, while others have more random spots. Here are some of the well-known types of koi:
  • Kohaku – White body with red spots
  • Taisho-Sanke – White body with red and black spots
  • Showa-Sanshoku – Black body with white and red spots
  • Bekko – Two-colored koi
  • Ki-Bekko – Yellow body with black spots
  • Goshiki – Mix of black, red, white, gray, and indigo
  • Utsurimono – Two-toned with black background
  • Asagi – Shiny, with metallic blue shades
  • Asagi-Shusui – Blue-gray with red and white markings
  • Koromo – Blue edges around the scales
  • Ogon – Shiny platinum color
  • Chagoi – Solid green or brown color, known for being very friendly
  • Kinginrin – Scales that sparkle and shine
  • Tancho – White body with a red circle on the head, similar to the Japanese flag

How to Care for Koi Fish

Pond Size and Setup

Koi fish should live in outdoor ponds, not in indoor tanks or aquariums. They need plenty of space and other koi around them to feel comfortable. The pond should be at least 3 feet deep to help keep the water temperature stable throughout the seasons and give the fish a place to rest in winter. The pond should be long and narrow if possible, which makes it easier to keep an eye on the fish and enjoy watching them. Plan for at least 200 gallons of water per koi. Keep in mind that koi grow quickly even if they start small.

Water Conditions

Koi like to dig in soft, sandy, or muddy pond bottoms. They eat more when the water is warm. When the water temperature falls below 45°F, they stop eating and rest at the bottom of the pond until the weather warms up. During this time, they barely move and rely on the mud for warmth. The pH level of the water should stay between 7 and 8.5, but never go above 9.

Plants and Shade

Aquatic plants can help clean the water, but koi might eat them. To protect your plants, place them in baskets that keep them out of reach. Use taller plants around one side of the pond to provide shade during hot weather, but do not block more than one-third of the pond from sunlight.

Filtration

Plants help, but they are not enough to keep the water clean. You will need a good pump and filter to remove dirt. A UV-C light filter can stop green algae from growing. Never fully drain your pond, even for cleaning. Instead, change one-fourth of the water every six months.

Can Koi Fish Live With Other Fish?

Yes, koi fish are peaceful and enjoy swimming in groups. They usually do well with other pond fish like tench or sturgeon. They are not aggressive and will not harm other fish.

What Do Koi Fish Eat?

Koi fish eat both plant and animal-based foods. When they are healthy and living in good conditions, they grow and may even start to breed. Feeding them high-quality food helps keep them strong and keeps the pond water clean. Feed them at the same time and in the same spot every day. This helps them get used to you and even lets you feed them by hand. If the water drops below 45°F, stop feeding them because they will enter their resting phase. If one of your koi does not come to eat, it may be sick or stressed. Watch it for 24 hours before taking further steps.

Keeping Koi Fish Healthy

If your koi fish gets sick, there are treatments available. But first, move the sick fish to a separate tank to avoid spreading illness. Here are a few basic health tips:
  • Check the water often. Use a simple water test to make sure the levels are right.
  • A strong filter helps remove harmful waste from the water.
  • Feed your fish high-quality food, especially in summer, to build strength for the colder months.
  • Do not overcrowd your pond. Each koi needs at least 200 gallons of water.

Breeding Koi Fish

In nature, koi breed based on size rather than age. Females usually become ready to breed between ages 3 and 5, and males between 2 and 3. They must be over 12 inches long. It helps to have more males than females—about two or three males for each female. Feed the females well before breeding season. When ready, the female lays her eggs in thick plant areas, and the male fertilizes them. The eggs hatch within 3 to 7 days, depending on water temperature. The baby fish stay still for the first few days and live off the energy from their yolk sacs. After that, they begin swimming and start eating small bits of natural food found in the pond.

Can You Keep Koi in a Fish Tank?

No, koi fish need too much space to live in a tank. Each adult koi needs at least 200 gallons of water, which is only possible in a large outdoor pond. If you follow the advice in this guide, your koi fish can live a long, healthy, and happy life in your garden.