do koi fish grow to their environment Do Koi Fish Grow To The Size Of Their Tank | Truth Or Myth |

do koi fish grow to their environment Koi Fish are pond fish that require a large amount of water to thrive well. Can they live in a fish tank? Yes and No. Let’s find out the reasons below.

do koi fish grow to their environment

Do Koi Fish Grow To The Size Of Their Tank

No. Koi is a member of the carp family that can tolerate temperature changes and water pollution to an extent more than other fish types. So, they will survive on smaller tanks with stunted growth. However, stunted growth doesn’t happen just by keeping it in a small tank. Koi’s body tries hard to grow as much as nature intended. And the end result is a larger fish that doesn’t move because of no space to swim. And unfortunately, Koi fish usually survive even in those circumstances.

Does the Size of a fish tank affect fish growth

For Goldfish, this statement can be true most of the time when the tank owner doesn’t change water frequently. Both Goldfish and Koi release a hormone to the water that affects their growth rate. The hormone percentage diluted in water determines how much bigger the Fish should be. If the tank owner changes water frequently, this percentage lessens, and the body of Fish thinks it’s ok to grow. So, the growth continues.

There are some written cases that Koi fish grew in a fish tank and couldn’t move any further to confirm this explanation.

How Large Can Koi Grow In Native Environment

A Koi can grow up to average 36 inches long and weighs up to 30 pounds depending on its environment and care level. Koi’s growth speed is affected by the pond’s size, health, feeding, water temperature, and water quality. And they reach their full potential within about 7 years.

Which Koi Grow Biggest do koi fish grow to their environment

Jumbo Koi is the largest type of Koi in the world. Some Jumbo Koi grow over 40 inches and live for up to 35 years. As another example Gost carp grows up to 18 – 26 inches.

How Long Do Koi Fish Live

Koi Fish can live from 20 to 200 years long, depending on their environment and care level. Usually, Kois live in Japan live longer. Koi’s average life expectancy in Japan is 40 years, while in other countries, it reduces to about 15 years.

How Fast Do Koi Grow In An Aquarium

A Koi grow for an average of 2.13cm per month for the first 6 months of its life. Then the growth rate reduces to about 1.74 cm per month for the next 6 months of their life. The growth rate decreases gradually and almost finishes when they are about 7 years old.

Keeping a Koi in an aquarium is not recommended because their growth rate doesn’t stop if you change water frequently (which you must) and give a proper diet. Kois are pond fish. They grow for around 9.2 inches long in their first year and about 15.6 inches at the end of their second year. So, an aquarium is not enough for a Koi fish.

Tank Requirement For Better Koi Growth

The ideal tank size for a Koi carp is at least 1000 gallons. If you have a Koi fry and plan to make a pond for it, you can temporarily keep them in a small tank. For this purpose, the fair rule of thumb is 1 inch per 10 gallons of water. So, if you have a 3-inch koi, you will have to keep it in a 30-gallon tank temporarily.

What Size Tank Does A Koi Fish Need

A matured Koi fish need at least 1000 gallon tank or preferably a pond to thrive. Kois continue to grow for around 10 years and up to 36 inches long, so they need a larger room to grow. If given lesser space than a minimum of 1000 gallons, it will be detrimental to both growth and longevity.

What Tank Decoration Koi Fish Prefer

Koi Fish prefer a natural environment with smooth gravel, rocks, and healthy plants. The easiest way to acquire Koi’s preferred habitat is to keep them in a pond. In a pond, you’ll have much room to decorate with various types of decorations, and they will love it.

How To Grow Koi Faster And Bigger

Koi’s growth rate depends on their environment and their care level. If you want your Koi to grow faster and bigger, you must ensure they have enough space to thrive and get a proper diet. Additionally, you must ensure their environment is free of toxins like Ammonia and Nitrogen as well as other harmful bacteria and viruses. They also need enough oxygens to grow well.


Koi are omnivore fish that will eat just about anything. They will eat from small bugs and insects to plants and algae at the bottom of the pond. They also eat store bought Koi fish food. Koi Fish need a variety of food to thrive well and not get bored of the food. If you provide them a nice combination of food, both meat-based and vegan-based, they will grow faster and bigger given they have enough space.


Fish hormones are used in the fish breeding process to increase fish production. It does not affect the growth rate of the Fish. So, you don’t have to inject any hormones into your Koi Fish unless you are a fish breeder.

Tank size

A Koi need at least 1000 gallons of water to grow bigger and faster. Most of their growth happens at their younger age, so you should introduce them to a larger pond when they are in juvenile Size. If not, their development may get stunted if you don’t perform water changing regularly. This will cause them to die at their young age.

Water Condition

The water condition plays a huge role in Koi fish growth rate. You must ensure that your pond has suitable water conditions for your Koi Fish to grow faster and bigger.

The Ammonia and Nitrate level should be at zero, and the Ph level should be at 7.2 to 8.0. The KH level should be around 105 ppm, and the GH level should be about 60 to 160ppm. The preferred temperature level is approximately 65 to 75 Faranhites.

Kois can tolerate temperature changes between 35 to 85 Faranhites; however, the temperature change should occur steadily. If a sudden temperature change happens, they may get stressed that leads to death.

Adding some salt to the pond is recommended to lower their health problems such as bacterial infections. A salinity of up to 5 ppt or 0.5 % is acceptable.


As Koi gets bigger rapidly, they need an excess amount of Oxygen for proper growth. A Koi need at least 5.0 mg/L of dissolved Oxygen in their water. Coldwater can hold more dissolved Oxygen than warm water. So, if your water temperature is warm, you should provide more Oxygen to your Koi fish.

A sure-find way to increase dissolved Oxygen is to install an air stone in your pond. You can also install a filter to remove fish waste to increase the effectiveness. Some people think installing an air stone and a filter is not essential for a pond, but if you need your Koi fish to thrive well, you should provide a good Oxygen flow to them.

Do Koi Grow In The Winter do koi fish grow to their environment

Yes. Although Koi don’t get feedings during the Winter and hibernate themselves below 5C, they continue to grow in the Winter. However, if the temperature goes below 2C they will die. So, if you live in an area that gets severe Winter weather, and if you want your Fish to survive in the Winter time, you should install a fish tank heater.

do koi fish grow to their environment How Much Do Koi Grow Each Year

As mentioned in the Koi Fish growth chart above, a Koi fish grow for around 9.2 inches in their first year and for about 15.6 inches at the end of their second year. They will be grown up to 20.1 inches at the end of 3rd year. And they will grow approximately 23.4 inches at the end of 4th year. They will reach their optimal growth when they are about 7 years old but will continue to grow until they get about 13 years old. The Maximum Size of a Koi fish is about 36 inches long and about 30 pounds in weight. However, Jumbo Kois grow bigger than that.

Check out also Koi Pond

Author bio

do koi fish grow to their environment Do Koi Fish Grow To The Size Of Their Tank | Truth Or Myth | 1

Dr. Chamika Siriwardhana

Dr. Chamika Siripardhana is a water and environmental researcher and the editor of life of fish website. He is a passionate fish keeper and has years of experience in the field. His mission is to help fellow aquarists experience the joy of fish keeping. You can find him on Facebook






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