how to grow big koi

The size to which koi can grow is simply amazing and continues to rise. Jumbos measure at least 30 inches and can weigh in at over 20 lbs. The magical metre mark has also been broken in the gosanke variety

It is a great accomplishment for a koi hobbyist to grow a 4 inch koi into a 2 foot one. It means both a healthy environment and proper care has been provided

the keys to growing big koi

#1 - Genetics
Genetics are predetermined physical traits expressed as a phenotype. If a fish does not possess the bloodline to develop into a large specimen, it simply will not despite the keepers diligence. The goal is of course for every fish to reach that size limitation. Most koi will reach an adult size of at least 20 inches if cared for properly

When selecting young koi, try to get a female with a larger head, backbone and over all frame. Knowing the bloodline is critical - large parents mean the chance for a big fish. Of course solid coloured fish such as Ogons, Chagoi and Magoi generally have the potential to grow larger than the more inbreed gosanke varieties

#2 - Age
If you want to grow a large fish, you have to start the process from birth. It is critical to put the framework and size on in place in the first 2-3 years and trying to grow a 15 inch 5 year old to 28 inches is a lost cause. I did sell an older Hariwake that I had for 1 year without any growth. I was quite surprised to see the fish later that Summer, it had put on several inches

#3 - Optimum Water Quality

WQ is pivotal. Everyone knows, we are water keepers first, fish keepers second . If there are chronic levels of Ammonia and Nitrite present, you will not only hinder growth, but will likely cause a disease state. Excess Nitrates will also slow growth down and pH needs to be stable and oxygen saturation a going concern. Provide chemically clean water and your fish have every chance to grow consistently and quickly

#4 - Pond Water Temperature

Although koi can adapt to life in lower temperatures, their ultimate growth potential will not be achieved. The optimal SET [standard environmental temperature] is in my opinion about 25-27 degree celsius. This will accelerate the metabolism and allow a tremendous amount of food to be fed

Although there can be a cooling down period for the fish in the Winter months, this period should be short and not extreme - 2-3 months with termperatures around 10 Celsisu. First year fish need to spend Winters in warmer waters or run the risk of being stunted. Remember, fish do most of their growth before sexual maturity, for males at 2 years, females mature at 3

#5 - Provide the Nutritional Blocks
Even if you provide all of the above, without proper nutrition, fish will not maximize their growth. Consider 6 or more small meals per day as fish are grazers with less than efficient digestion Because koi are heavily vegetarian their diet should include dark green leafy vegetables. The key words variety, freshness, nutrient content and frequency all apply

#6 - A large deep pond

Obviously the pond dynamics are important. It is not by coincidence that fish put on the best growth in low stocked high water volume mud ponds. These large deep ponds allow fish to exercise and develop their musculature as well as provide lots of natural food. This scenario mimics nature with the added benefit of fish not wasting energy looking for food and just focusing on growth. A smaller pond can be made to appear larger by installing jets, you will not match the magic of a mud pond
Putting it all Together
As mentioned, these items are all critically important. If you can incorporate all of the keys, there will be a synergistic effect and fish should put on great size quickly. 1 year old Tosai can be over 16 inches and in successive years, 4 - 6 inches can be added. As the fish approach 5 years old [Gosai], growth will slow down but this also depends on the bloodline. Dainichi fish can grow a long time, up to a decade

I once had a growing contest with one of my friends. We both had 35 gallon tanks and each purchased one 2 inch fish to grow. After 6 months, my fish was almost 8 inches while his was just 3. I attribute this growth to my home made filter, weekly water changes, heating and the live tubifex worms which I fed 3 times a week
  • This fish went into the mud pond in April at 8-9 inches...
  • It is a great idea to measure koi regularly to track their growth
  • ...It came out in November at 16" for a growth rate of 1 inch per month


Watch a 1hr. video on how to grow jumbo koi