How Fast Do Koi Fish Grow? (With Chart)

How Fast Do Koi Fish Grow? (With Chart)

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Koi fish are popular ornamental, freshwater fish that are typically kept in ornamental ponds. They were originally taken care of by rice farmers in early 19th-century Japan and are essentially colorful versions of the common carp, although they most certainly aren’t common! The word “Koi” actually translates to “love” or “affection” in Japanese.

If you’re considering purchasing or have recently purchased a Koi, and you’re wondering how big they get, you’ve come to the right place. We go over the sizes that you can expect and other pertinent information, such as factors that can affect your Koi’s growth.

How Big Will My Koi Fish Grow?

The average Koi fish, when fully mature, can measure up to 3 feet (36 inches) in length and can weigh 22 to 26 pounds! This is not to say that every Koi fish will end up this large, however, as several different factors might influence how large your Koi will become.

Domestic Koi kept in an aquarium might only grow to be around 12 to 15 inches, and the more traditional Japanese Koi can grow up to 26 inches in length.

These sizes depend on the type of Koi fish that you have. There are over 100 different kinds of Koi that all come in different sizes. The size of a mature Koi is typically dependent on the species more than on its environment, but the environment will still have an impact on the Koi’s growth rate.

Koi Fish Growth Chart

This chart is based on the growth rate of the average Koi, so not every fish will be the exact size that you see here. This is just to give you a rough idea of what you might expect as your Koi matures.

Age	Koi Fish Size
1 month	1.1 inches
6 months	5.1 inches
12 months	9.2 inches
18 months	12.6 inches
2 years	15.6 inches
2.5 years	18 inches
3 years	20.1 inches
3.5 years	21.6 inches
4 years	23.4 inches
4.5 years	24.6 inches
5 years	25.7 inches
5.5 years	26.6 inches
6 years	27.3 inches
6.5 years	28 inches
7 years	28.5 inches

Source: http://www.bycaitlin.com/Koi Fish-and-koi.html

How Fast Do Baby Koi Fish Grow?

The size and colors of each baby Koi will depend on what kind of Koi you have. Just like with the previous chart, this is an average idea of what you can expect from your Koi as it matures, but the numbers won’t fit every fish exactly.

Weeks 1–6

On average, a baby Koi grows approximately .03 inches (.071 cm) every day until it is about 6 months of age. So, your Koi by Week 1 will be about .20 inches (.5 cm), and by 6 weeks, it could be 1.2 inches (3 cm).

The baby Koi might be brown in color at this age, or it might be the orange or red that we typically see in the adult, but the colors won’t be as bright as they will be when it matures. They could also be white, yellow, black, or gray.

Months 2–6

By 2 months of age, the baby Koi will be about 1.6 inches (4 cm), and by 6 months, the Koi could be as much as 5.1 inches (13 cm).

The Koi’s coloring should continue to develop at this time. You might find that the color changes and will deepen and will become more noticeable.

Months 7–11

When the Koi reaches 6 months, the growth rate starts to slow down to 0.2 inches (.06 cm) every day until it’s in its second year. By its 7th month, the Koi will be about 5.8 inches (15 cm), and it will continue to grow at roughly the same rate.

The colors of the Koi will change and grow brighter and deepen as it continues to mature.

1 Year

By the time your Koi is in its first year of age, it could be around 9.2 inches (23 cm), but again, it could be smaller or larger, depending on the species and your Koi’s environment. The growth is about .21 inches (0.5 cm) per day into its second year.

2 Years

When your Koi reaches its second year, it will be about 15.6 inches (40 cm). The daily growth rate will continue to decrease as it continues to age.

By its second year, the Koi’s coloring is typically at its peak.

3 Years

For some Koi, they are already at their adult size, between 15 and 16 inches, but for others, they could reach 20 inches or more by the time that they are 3 years old. It takes the Koi about 3 years to become a fully mature adult.

How to Avoid Stunting Your Koi Fish

There are a few factors that can stunt your Koi’s growth. Interestingly, fish that are stunted do tend to live longer, but it’s up to the fish keeper if they want to actively stunt their Koi’s growth or make their fish as comfortable as possible throughout its life.

Stunting typically occurs due in part to stress or illness, which can develop under the following conditions.

Tank/Pond Size

The general rule is that each adult Koi needs a minimum of 250 gallons for each fish. If you have a female that is capable of spawning, you’re looking at 500 gallons for each female. But bigger is always better.

However, it’s highly recommended that you don’t confine Koi to a tank, but rather give them a home in a pond. The pond should be at least 1,000 gallons and 3 feet deep.

Overcrowding

An overcrowded tank will most definitely stunt your Koi’s growth. If you have a pond that only holds 1,000 gallons, you should only have about three or four medium-sized Koi or two large Koi in total. The more Koi there are in a confined space, the more the water quality will suffer, and your Koi will become stressed.

Temperature

The temperature should be about 60°F to 75°F. While Koi can handle temperatures below and above this range, the water quality can deteriorate outside of their preferred temperature.

Diet

A Koi will thrive with a good diet. You should be sure to store the food properly and throw away any excess food leftover after 6 months of being opened, regardless of the date on the package. Pellets that are high in protein and contain enough vitamins and minerals are what you should invest in.

What and how much you feed your Koi will definitely contribute to its growth rate.

Water Quality

• The optimum pH levels are about 7.0 to 8.5.
• Ammonia levels should be 0 (you don’t want to see levels of 0.25; any higher and you’re risking your Koi’s life).
• Nitrates should be at about 20 to 60 ppm.
• Nitrites can be less than 0.25 ppm but really should be at 0.

How to Make My Koi Fish Grow Faster

As long as you follow the suggested conditions listed in the previous section, your Koi will thrive and grow much bigger, much faster!

Their environment must be large and warm, with the right pH, nitrite, and nitrate levels, and be well-maintained.

As your young Koi grows, particularly if you have it housed in a tank, it must be moved to larger living quarters, whether a larger tank or best of all, a pond.

Feed it a high-quality diet of pellets, along with bloodworms, brine shrimp, and a few vegetables.

Remember, your Koi will only grow as large as its genetics will allow it to.

How Big Do Outdoor Koi Fish Grow?

It’s quite possible for your Koi to grow large and rather quickly in a pond. However, if you have a small pond, they could still suffer from stunted growth, particularly if the water quality isn’t what it should be.

The pond should be heated (especially for colder weather), and you still need to give them a high-quality diet, as these factors will always be part of what contributes to a healthy and potentially large Koi.

Final Thoughts

It’s great that you’re taking the time to figure out how large your Koi will grow, as it can also help you figure out how to set up its habitat. In addition to its diet and water conditions, the species of Koi is an important factor that will determine the size of your Koi.

We hope that our article has helped answer a few of the questions that you may have regarding your Koi’s growth. Enjoy your time raising these beautiful fish!

Featured Image Credit: Just Koi, Unsplash