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How Fast Do Koi Grow?


Under the right conditions, the average Koi will be between 6 and 8 inches by the end of its first year, and by the time it is 3 years old it will have reached its full adult size.

Koi Growth


An average Koi is able to grow to between 24 and 36 inches in length, although some ‘jumbo’ varieties of Koi are capable of reaching up to 52 inches. Impressive sizes are only achievable, though, if the pond conditions are optimal and if the pond itself is large enough. In any case, getting your Koi to grow to these formidable sizes is not going to be an easy task.

When it comes to the size of the fish, especially if you are attempting to breed the larger varieties of Koi carp, there are several factors that need to be taken into consideration. These include:

  • Genetics
  • Age
  • Water quality
  • Pond temperature & size
  • Nutritional blocks

Koi Genetics


Genetics of the Koi play a huge role in determining just how large the fish is going to be, and if a particular Koi does not possess the required predetermined traits, then it simply will not grow into a large specimen - regardless of how ideal the pond environment may be.

Due to genetic predispositions, most Koi will reach a size of 20 inches if cared for properly and in the right environment.

Under the right conditions, the average Koi will be between 6 and 8 inches by the end of its first year, and by the time it is 3 years old it will have reached its full adult size.

Breeding Large Koi Carp


If you are hoping to grow larger Koi, then you should start with a young female. Try to select one with a large head and backbone. Of course, if you can find out about the lineage of the fish (did it come from large parents) then that will also give you a head start.

Diet is a major influence in the growth potential of Koi carp and it should be looked into carefully. Two of the most important things to remember are the fact that fish are grazers and if fed too much, a lot of it is simply wasted. High protein feed, such as Saki-Hikari, should be given in relatively small amounts 5 or 6 times a day.

Another thing to keep in mind is the hormones which are released into the water by the Koi carp. When these hormones reach a high enough concentration, the Koi will simply stop growing (egg production will also stop). This how they maintain a natural balance in the wild and prevent over population.

Two things to keep in mind here, then:

  • Low numbers of fish in your pond
  • Good water quality


These two steps alone will go a long way in helping to promote growth in your Koi carp. 250 gallons per Koi is ideal regarding water volume. Keeping to this ratio and maintaining good water quality will enhance your chances of achieving impressive growth.

Most keepers use outdoor ponds for their Koi and this is preferable to indoor aquariums for multiple reasons including the natural day/night cycles and also because of the feeding opportunities that insects present.

  • Header image of orange Koi by Adam Jones via  ()

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