How Big Do Koi Fish Get & How Fast Do They Grow?

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The koi fish that we are currently familiar with was created via artificial breeding from wild fish that Japanese rice farmers had first captured. Koi are simply brightly colorful types of Amur Carp. You may be curious about how huge a koi fish could become if you plan to raise this gigantic species in your home tank.

Koi fish typically reach a maximum size of 36 inches during their adulthood. They increase at a pace of 0.8 inches every month, based on the type of koi you possess.

How Big Do Koi Fish Get

Now that you are aware of how quickly and how huge koi fish may expand, let’s examine this in detail. We will explain everything about how big they could grow in the right environments, what factors affect their growth, and the biggest koi fish discovered to this date. We will also go through the optimal water parameters for koi fish growth and well-being.

Koi Fish Details (Cyprinus Rubrofuscus)

  • Care Level: Medium
  • Temperament: Peaceful
  • Appearance: A white or silver body having a dash of red, gold, or orange patterns
  • Lifespan: 25-35 years
  • Size: Between 24 and 36 inches
  • Diet: Omnivorous
  • Family: Cyprinidae
  • Tank Size: 250 Gallons

How Big Do Koi Fish Get?

Although original Japanese koi could reach lengths of approximately 26 inches, captive koi fish variants can reach lengths of 12 to 15 inches when kept in aquariums. Jumbo koi variants may expand to be around 36 inches long and range between 22 and 26 pounds in weight. They were specifically chosen to increase their overall weight.

Each variety of koi fish (there are over 100 variations!) falls into various sizes group, which is due to the fact that their growth as complete adults is generally connected primarily to their biological composition rather than to the habitat in which they live.

One common misconception about koi fish seems to be that they can only expand as big as the tank (or canal) in which they live. This myth is not backed out by any research, although it does have some truth to it since the size of an aquarium has a huge impact on how big a koi fish would grow.

Similar to humans, koi fish’s development is significantly influenced by a variety of things, including weather, water condition, and the nutrition they are provided during their lives.

The myth does not prove that it is a koi fish’s annual maturation, not its size, that would be determined by factors such as tank size and other factors.

If you want your fish to expand as quickly, you could manage the environmental elements that influence their rate of growth by providing the greatest level of care. But it won’t get any bigger than its genetically determined size limit!

How Long Do These Species Take to Grow to Their Full Adult Size?

The majority of koi fish species reach adulthood within the first 3 years of life. Since certain breeds of ornamental fish could survive even into their sixties, that is often seen as a high speed of development (especially the Japanese koi). Captive koi fish can grow to be 9 inches long when it turns around one year.

As compared to Japanese-bred koi fish, European-bred variants sometimes possess significantly faster development rates; however, such traits are often followed by shorter lifespans.

How Fast Do Koi Fish Grow?

How Fast Do Koi Fish Grow

Depending on what type of Koi you own, every young fish would have a different size and appearance. These statistics demonstrate an approximate understanding of how long your koi fish could grow as it reaches adulthood, but not every fish will expand completely according to these numbers.

Koi growth chart:

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

Weeks 1–6

When a baby Koi is less than six months old, it typically develops by about.03 inches (.071 cm) every day. As a result, your pet would be roughly .20 inches (.5 cm) long around Week 1 and can turn out to be 1.2 inches (3 cm) long around Week 6.

The young Koi could be brown during this stage, or it could be golden or a shade of red that people usually observe in grownups; however, the pigments would not stay vibrant while it grows. Alternatively, they might be grey, black, pale white, or even yellow.

Months 2–6

Baby Koi can reach a height of approximately 1.6 inches (4 cm) at the age of two months and up to 5.1 inches at 6 months (13 cm). Now is a good time for Koi’s colors to flourish. You can observe that the coloration transforms, intensifies, and stands out more.

Months 7–11

By the time the Koi is six months old, its growth speed has decreased to 0.2 inches (.06 cm) daily, where it will stay the same until it turns two years old. When the koi grows older, its colors would develop, get brighter, and get deeper.

1 Year

As previously said, based on the breed and your fish’s habitat, it may grow smaller or bigger till it gets one year old, which is estimated to be 9.2 inches (23 cm) long. The average growth of a two-year-old koi is approximately .21 inches (0.5 cm) daily.

2 Years

Your Koi can grow around 15.6 inches (40 cm) in length during its second birthday. As it gets older, the percentage of continuous growth would eventually fall. The Koi’s color tends to reach its finest during its second year.

3 Years

Many Koi are almost adult-sized, measuring around 15 to 16 inches, while others may grow 20 inches or above by the age of three. Koi needs roughly three years to reach adulthood.

Factors That Influence a Koi Fish’s Growth Rate

Koi fish usually develop at the exact same speed in their first year. After this point, factors like how well they are fed, the water conditions of their aquarium, etc., will influence how quickly they grow. The following are the key elements that might affect a koi fish’s growth speed:

Water Temperature

No matter what kind of koi we are dealing with, keeping them in tanks would cause them to thrive more quickly than keeping them in ponds.

An increase in water temperature plays a significant role in this rapid growth process. Additionally, there aren’t as many temperature changes in a tank.

In order for your koi fish to expand more quickly, it is best to maintain a water temperature that stays consistently between 75 and 80 degrees Fahrenheit.

It’s among the key factors behind why koi breeds originating from the west and grown there often develop quite faster than koi exported from Japan. Fishkeepers in Japan don’t heat water tanks in the cold, allowing their koi fish to hibernate beneath a blanket of ice, which as a result reduces their metabolism.

Koi owners may significantly control a koi’s development rates by controlling the water temperature in an aquarium or canal, although faster growth could result in reduced longevity.

Water conditions for a koi fish in a tank

  • Oxygen level: 5.0 mg/L
  • Water pH: 6.8-8.2
  • Water KH: 105 ppm (+/-15 ppm)
  • Ammonia: 0
  • Nitrites: Below 0.25 ppm
  • Nitrates: 20-60 ppm


The common perception about koi fish seems to be that they are strong freshwater species that could tolerate the most adverse environmental conditions. However, extremely stressful conditions can cause a lot of damage to them.

What causes stress to fish in ponds and aquariums? A few stressors that might adversely impact a koi fish’s development speed are continuous changes in water conditions, water temperatures that are inhabitable for them, mismatched tank companions, overpopulation, and insufficient oxygen levels.

If your koi become infected with KHV, have pathogen invasions, or other illnesses, their growth might suddenly stop.


Koi fish are naturally omnivorous, meaning they will consume just about anything. In addition to being food addicts, they are quite easy to train for fish keepers who want to teach them hand feeding. They’ll do everything to get food and treats.

Despite the fact that these animals are food-driven, many nutritional guidelines are helpful if you wish to speed up a koi’s maturity without facing the possibility of overfeeding and the health concerns associated with it.

It is best to feed a diet full of protein that includes seafood that is nutrient-dense and loaded with essential micronutrients. The best method for increasing the development speed of any fish kept in confinement is to give them a balance of protein, carbohydrate, and fatty components.

Despite the fact that they’re going to consistently nibble on aquatic plants and hoover the base of an aquarium in search of more food, what you give them is going to have a huge impact on their development speed than their ability to hunt for themselves.

Koi’s development speed would be considerably slowed down if they are not given sufficient food or if they are kept on a monotonous diet (similar feed every time).


Koi fish may develop more slowly if they are overcrowded in a tank, and by doing this, you may even kill some fish. The majority of koi fish, if housed together in a poorly-sized tank, won’t even survive a single year.

If a tank is packed with koi fish, their messiness will overpower the tank’s colony of beneficial microorganisms. Nitrifying (friendly) microorganisms are the most effective filter for removing impurities from aquarium water and preserving biological equilibrium.

If healthy bacteria cannot keep up with the expectations of maintaining proper water conditions, the environment in your aquarium will become poisonous (ammonia toxicity!). A pond filled with too many koi might experience a similar thing.

Koi fish development is negatively impacted by the lack of swimming and exercise rooms since it is a stressful situation. Therefore, be confident you would meet their tank/pond size requirements if you wish to maintain a healthy, quickly expanding community of koi fish in your aquarium.

  • Small Koi fish (2 – 8 inches): 100 – 150 gallons of the tank;
  • Medium Koi fish (8 – 14 inches): 250 – 300 gallons of the tank;
  • Large Koi fish (14 – 24 inches): 400 – 500 gallons of the tank;
  • Jumbo Koi fish (24 – 36 inches): 750 – 900 gallons of the tank.


The biological composition of a koi would have a considerable impact on how quickly it could develop, similar to how it determines how huge it evolves while they are stepping into adulthood.

European koi breeders have worked hard to develop the quickly maturing contemporary household koi that we are familiar with, including some indoor variations hitting their stage of maturity in their second year.

Koi fish cannot develop any faster than their genetic composition, despite all other possible factors. When koi are young, their growth usually occurs at the fastest speed. This one-year growth spike is controlled by genetics.

Fishkeepers would have the most control over their pet’s development speed throughout their maturity, during which they may easily grow twice or thrice their size. Koi fish’s natural development may slow down as they turn old.

In fact, this rule does not apply in all situations. A baby with bigger, faster-growing genes seems to have a better possibility of experiencing a massive increase in the first 2 years of birth than those with tiny, slower-growing genes.

Biggest Koi Fish

Geoff Lawton has the world’s largest koi, “Big Girl,” a Japanese-sourced koi fish. Big Girl currently measures an amazing 48 inches and weighs 90 lbs.

The Big Girl has been the biggest fish to ever join the selection of supersized koi belonging to the Japanese specialist producer prior to getting purchased by its master.

Its owner housed Big Girl in its individual pool in his pet store and fed her around 1 pound of high-quality fish pellet daily to maintain a healthy weight.

Read More:


How Big Do Butterfly Koi Get?

Butterfly koi, commonly referred to as Dragon carps, may reach a length of 24 inches, but some of them could even grow close to 36 inches. Their long, powerful, swirling fins may give the impression of a taller body.

How Long Do Koi Live?

The majority of koi fish may survive for 20 to 30 years if housed in the proper setting. The oldest documented koi fish survived for 230 years! They can live longer depending on a number of factors.


The advanced techniques for boosting your koi fish growth may seem overwhelming to a beginner koi fish keeper. In fact, they are among the most low-maintenance aquatic species in this size range.

If you’re worried about your koi’s growing speed, you can speed up their growth with the help of this amazing guide and useful tips. In no time, you will observe an aquarium full of extraordinarily large koi.

You can help your pet to thrive by providing it with steady water temperature, balanced nutrition that can fulfill its dietary needs, enough room to swim around, and a stress-free environment.

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1 thought on “How Big Do Koi Fish Get & How Fast Do They Grow?”

  1. I’m currently pulling down my swimming pool in which I have 4 Japanese koi. 2 are very large at about 15″ or more and 2 medium size, plus about 20 goldfish. A cormorant bird took about 100 small Goldies last year. Because I have to cover the pool which defeats the purpose of watching the fish and water Lillies etc. I’m moving the koi to a smaller pond as I’m finding at 78 years and widowed 11 years ago it is difficult to keep up the maintenance. Your comments have been very helpful for me, especially about the rate of growth for koi. Thank you


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