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How Fast Do Koi Fish Grow? What You Need To Know!

Koi are a popular species of freshwater pond fish that can develop at a rapid rate. Koi are usually kept in freshwater ponds and, depending on their living conditions, have an average lifespan of 25 to 30 years.

Koi fish come in a variety of colors and patterns, but they always share one characteristic: they develop extremely quickly.

Many aquarium keepers are astonished by how quickly their koi fish grows, which produces a great deal of confusion over the appropriate pond or tank size for this enormous fish.

If you are interested in purchasing koi and are curious about their maximum size, "How Fast Do Koi Fish Grow? What You Need To Know!" by BestForPets (bestforpets.org) will provide you with all the relevant information.

Do Koi Fish Grow Quickly?

Yes, koi fish grow at an average pace of 0.8 inches (2 centimeters) per month. The pace of growth of your koi fish depends depend on their species, food, and living conditions.

Koi achieve their maximum adult size within the first two years of life, after which their development rate slows to 0.4 inches (1 centimeter) every month.

The growth of koi affects not only their length, but also their body width. Due to the exceptionally long fins that extend from their bodies, long-finned koi types may appear to be larger. Some koi will grow quicker than others, depending on their genetics and living conditions relative to other koi.

Juvenile koi develop the quickest in optimal settings, and their growth will begin to slow after a few years.

How Big Do Koi Fish Grow?

A mature koi fish can reach a maximum length of 36 inches (91 cm) and weigh up to 20 pounds. However, not all koi fish will reach this size, as the average koi only grows 20 to 24 inches (50 to 60 cm) in length and weighs 9 to 12 pounds.

The adult size of your koi will depend on the kind, as some koi variations are genetically predisposed to grow significantly larger than others.

Consider the average size of certain koi:

  • Domestic koi: 12 to 17 inches in length
  • Japanese koi: 22 to 26 inches in length
  • Butterfly koi: 24 to 30 inches in length
  • Jumbo koi: 32 – 36 inches in length

Koi that are genetically larger than other types may have a quicker development rate than other koi; but, as they age, their growth will diminish.

What Influences a Koi Fishes Growth?

Several circumstances can affect the growth rate of koi fish, and some large-growing koi kinds may not achieve their usual adult size if these factors have an effect on their growth.

Pond Size

If kept in a small pond or aquarium, Koi fish cannot grow to be very huge. The size of the pond will also effect the water quality, as small bodies of water that are overpopulated with koi fish will quickly become unclean, which can negatively impact the fish’s health and longevity.

Since koi are enormous, fast-growing fish, they must be raised in a large pond with filtration and aeration to maintain their health.


If a koi fish lacks the DNA to grow huge, the largest pond, the best diet, and the cleanest water will not affect its potential adult size. Some types of koi, such as the butterfly and giant koi, have the genetics to grow to an average size of 30 inches (76 cm).

Stocking Rate

If you overcrowd your koi in a pond or tank, there will be less area for the fish to swim. In addition, the bioload in the pond will grow, which will have a negative influence on your koi and may cause additional stress, making them more susceptible to disease.

It is equally crucial to stock your large koi pond correctly as it is to ensure that each koi has sufficient space to grow and move freely.


The growth rate of Koi will peak during their first two years of life and then gradually diminish as they age. If a koi fish did not grow properly during its prime growing years, it may be difficult for the fish to grow larger after the age of ten.


Koi fish require a nutritious and well-balanced diet to give them with the essential nutrients for appropriate growth. Young and growing koi fish will take more food since they require additional nutrition for growth.

Adequate diet is required for the duration of a koi’s life, although additional vitamins and minerals are beneficial during their developmental stages.

Water Quality

If you wish to accelerate the growth of your koi fish, water quality is an additional factor to consider. The water parameters (ammonia, nitrite, and nitrate) have a part in the health and growth of your koi fish; however, additional water quality factors such as pH, alkalinity, temperature, and dissolved oxygen also influence your koi fish’s growth.

How Long Does It Take For Koi To Grow?

The average koi fish can live for 20 to 35 years, and their growth often slows after three years. After this stage, koi fish may continue to grow between 4 and 6 inches per year until they reach their ultimate development stage at 10 years of age; however, some koi continue to grow until they are 12 years old.

Why Do Some Koi Grow So Slowly?

In addition to diet and pond size, genetics play a significant part in determining the growth rate of your koi fish. Stress or illness may be the cause of your koi’s sluggish growth, and this can be caused by inadequate housing and water conditions.

To prevent their growth from being inhibited, koi require a large pond, the proper feed, and an adequate quantity of fish. A stunted koi fish will fail to reach its proper size due to genetic anomaly, but hunger and poor water quality in a confined setting may lead your koi to have stunted growth.

How To Make Your Koi Fish Grow Faster

If you wish to rear healthy young koi so that they grow swiftly without being hampered, then the following advice may be useful:

  • Maintain your koi in a big pond with a depth of between 3 and 5 feet.
  • Ensure the pond has an effective filtration and aeration system to improve the water quality for your koi fish.
  • Avoid overstocking the pond with koi so that each fish has sufficient room to grow and move.
  • Give your koi a balanced meal made specifically for koi fish that contains vitamins and minerals to aid in their development.
  • Feed young koi two to four times per day with pieces of the appropriate size.
  • Keep the appropriate water chemistry for your koi.

Final Thoughts

We hope “How quickly do Koi grow? What You Should Know!” by BestForPets (bestforpets.org) answered your concern about koi growth rate.

Many inexperienced fish keepers may be intimidated by the rapid growth rate of koi fish, but once you have set up the perfect sized pond with the proper water conditions and diet, you will notice that your koi fish will develop steadily for the first 10 years of their lives before slowing down.

Koi fish grow at varying speeds, but the majority of their spectacular growth occurs within the first three years of their lives.


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Dr. Deborah Fletcher

Deborah R. Fletcher, DVM, is a skilled veterinarian with more than 15 years of experience dealing with companion and exotic animals. She has experience caring for a variety of animals, including household cats and dogs, reptiles, birds of prey, and even primates. Dr. Fletcher is a valuable part of the BestForPets team, where she contributes to their aim of providing pets and their owners with the finest possible treatment and services.

Veterinarian (DVM) Dr. Deborah Fletcher


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