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Breeding Koi Fish: Step By Step Guide

Sarah Psaradelis

By Sarah Psaradelis

koi fish in aquarium

Breeding koi is an excellent way to expand your koi fish collection and produce different varieties and colors of koi. There are many ways to go about breeding koi fish, but not all methods will be successful.

Over time, you will be able to learn the do and don’ts of koi genetics and which lines produce certain colors and patterns. It can take years to master the skill of koi fish breeding, and there’s more to the breeding process than placing two koi together and hoping for the best. This article will detail a step-by-step guide you can follow if you want to breed your koi fish successfully.

What You Need To Know Before Breeding Koi Fish

Before you start breeding koi fish, this is what you need to know.

Sexual Maturity

You must choose the right breeding pair of koi fish before you begin. This is because you need to ensure that the parents will be healthy and have no history of any issues that can be passed on to their offspring. The breeding pair needs to consist of one male and female koi fish, ideally over the age of 3 years old.

Koi will only become sexually mature at around 3 years of age, although some koi mature slower depending on their size. At 3 years old, healthy koi raised in the right environment will be approximately 10 to 12 inches in size, which is an indication that they are sexually mature.

At around 7 to 9 years of age, the female koi will stop depositing eggs and will no longer be able to be used for breeding.

koi fish
Image Credit: Just Koi, Unsplash

Koi Reproduction

As oviparous breeders, female koi fish do not carry the fry or eggs inside of them. Instead, she will carry the unfertilized eggs and release them into the water during spawning. The whole reproduction process of koi fish is done externally. The male koi will deposit his sperm over the eggs to fertilize them.

Only once this process is done will the eggs become fertilized and begin to develop. Once the eggs have been fertilized, the koi do not play a role in protecting or parenting the fry. Due to the lack of parental care for their offspring, the parents and other koi in the pond will eat any eggs and fry that they can find. The female koi will first carry the eggs during the cooler months, giving her a fuller appearance with a steady-growing abdomen as the warmer months approach before depositing them for fertilization.

Breeding Season

Even if your koi are sexually mature, the environment still needs to be suitable enough for them to breed. Most koi fish won’t spawn in dirty and cold water out of their breeding season. In the wild, koi will spawn between the late spring and early summer months.

Number of Eggs

A female koi fish can produce up to 100,000 eggs during the breeding season. This is typical for most healthy female koi weighing around 2 pounds. For smaller koi around 1 pound in weight, the number drops between 50,000 to 80,000 eggs during the breeding season.

This is a lot of eggs and the number of fry that hatch can be overwhelming. This makes it important for koi fish breeders to be prepared to raise, feed, and house lots of koi fish. However, not all of the fry will hatch successfully, so the number can vary significantly depending on how the eggs are raised. Koi eggs are translucent and delicate, so they should be handled with care.

Preparing To Breed Koi

koi fish eating pellets in pond
Image Credit: Michel Lombard, Pixabay

Ensuring that you have the right equipment to raise and breed your koi is essential. Fortunately, you can source these items for a relatively affordable price and reuse them for each spawn.

So, here’s what you will need:
  • A large tub or pool that holds a minimum of 100 gallons of water. It can be thick plastic, metal, or cement depending on its location and your preference.
  • A sponge filter and air pump.
  • Food for the fry.
  • Netting, rope, brushes, or plants for spawning.

Step-By-Step Guide To Breeding Koi Fish

1. Choose a Breeding Pair of Koi Fish

You will need to choose two healthy and sexually mature koi fish over 10 inches in length and between the ages of 3 to 5 years old. One will need to be identified as a sexually mature female and the other as a male. Female koi fish are usually larger with rounded bellies, whereas males are slenderer and have slightly more pointed fins than females. The female koi will have a pinker and rounder vent, which is where the eggs are deposited from.

koi fish pond
Image Credit: Else Siegel, Pixabay

2. Provide the Correct Breeding Conditions

Once the cooler water begins to warm up in the early spring, koi will begin spawning. If you want to breed your koi, you will need to replicate or follow the necessary breeding conditions. This means keeping the water clean and fresh, with a filter or pump oxygenating the water constantly. The temperature should ideally be between 65 to 70 degrees Fahrenheit, and it should not be too hot or too cold for the koi.

3. Place the Breeding Pair in a Spawning Tub

It will be tedious to sit removing the eggs from the koi pond where the adults are kept. This process may also damage some of the eggs, and there’s no guarantee that you will select each one. Since koi will eat the eggs and any of the young, the eggs should be kept separately. To make this easier, you should place the breeding pair in a separate holding place.

Ideally, this should be the tub you plan to raise the fry in. The tub should consist of a sponge filter that does not produce a strong current, only enough to prevent the water from becoming stagnant. The sponge filter has too small of an opening to suck in the eggs or fry, making it safe.

koi fish in fresh water aquarium
Image Credit: Arunee Rodloy, Shutterstock

4. Provide Spawning Materials

Although this is not necessary, it can ensure that the eggs are kept secure. The female koi will have no problems depositing her eggs on the base of the spawning tub, but placing netting, spawning brushes, or live plants such as moss or hornwort can soften the egg’s landing and keep them protected. When the eggs hatch, these spawning materials can offer the fry security rather than being left out in the open.

5. Watch the Breeding Pair for Spawning Behavior

When the breeding pair of koi is ready to spawn, the male will chase the female around. This process might seem aggressive and can stress the female out during the time. However, it encourages the female to deposit the unfertilized eggs she has been carrying.

If you have placed spawning materials inside of the breeding tub, the eggs will attach to it or fall to the bottom. Don’t be alarmed if the water developed a foamy substance on the top. This is an indication that the spawning has been successful, and it will go away after the next few days.

koi fish kissing
Image Credit: gunungkawi, Shutterstock

6. Remove the Breeding Pair

Once you are sure the eggs have successfully been fertilized, you should remove the breeding pair from the spawning tub. They will soon eat the eggs and any fry that hatched as neither the female nor male koi looks after their offspring. You can place the koi back into their main pond with the others or separate them into a male or female-only pond if you notice any aggressive breeding behaviors from the male koi.

7. Monitor the Eggs

The fertilized eggs in the spawning tub will hatch after 4 to 7 days, and soon you will notice thousands of fry swimming around. During these 4 days, it is a good idea to monitor the eggs. Any unfertilized eggs will begin to develop a fluffy white appearance, which is an indication of fungi growth. Any eggs with fungi should be removed before the fry hatch to keep the environment hygienic for the soon-to-hatch fry.

8. Raising the Fry

After hatching, the koi fry will feed on the egg sac for the next several days. You won’t be feeding the fry the same diet as the adults eat since they are too small. Instead, the fry should be fed baby brine shrimp, crushed koi pellets, egg paste, powdered krill, or daphnia up until they are 3 weeks old. They can be kept in the spawning tub if it is over 100 gallons in size with the sponge filter until they are large enough to be moved into the adult pond.

koi fish eggs on a brick
Image: Mr. Piyapong, Shutterstock


If you want to breed your koi, you will need the budget, space, time, and knowledge to do so. While it might sound fun to breed koi fish, it can be slightly more challenging than you might think. You will also need to ensure you have a method of selling or homing the fry the breeding pair produces since you probably don’t want to sit with thousands of koi fish and nowhere to put them all once they start to hatch and grow.

Featured Image Credit: TigerStocks, Shutterstock

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