How to Make Koi Grow Faster (Maximize Koi Growth)

Koi are intelligent and beautiful fish with the potential to become quite large and vibrant if properly taken care of. Most healthy koi are able to reach three feet in length (sometimes more) by the time that they attain full maturity at ten years of age. However, this is heavily influenced by things such as water quality, diet, stress, stocking, and many other factors.

The largest koi on record, named Big Girl, is four feet long and weighs an incredible 91 pounds. Her size is largely attributed to her breeding line and eating over a pound of well-balanced pedigree food per day. Establishing a trusting relationship with your koi, as well as a good feeding and cleaning routine early on can help to really maximize growth from fry to adult.

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Just How Fast & Big Can Koi Grow?

Most koi are able to achieve a maximum size of approximately 3 feet in length and a weight of around 12 pounds by the time they reach adulthood at ten years of age, if properly taken care of.

The first couple of years are a time of quick growth for koi, with them growing half of an inch to an inch per month. After two or three years, growth slows down to a quarter to half of an inch per month, though this varies depending on the season (growth is, of course, slowed or stops altogether in the winter depending on conditions), food availability, food quality, stress, illness, and stocking.

A study conducted on domesticated koi fry fed a daily diet supplemented with zooplankton experienced 49 to 67% more weight gain and growth than those without. This makes sense given that cyprinid species, including koi’s wild common carp cousins, feed heavily as fry on naturally occurring zooplankton in the water such as protozoa, rotifers, and cladocerans.

Common carp also grow much more quickly than koi, partially due simply to their genetics but also likely their environment and diet. Within 5 years they reach their maximum size of over a meter, or approximately 3.5 feet, with a substantial weight of 33 pounds.

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What Factors Can Limit Koi Growth?

1) Koi Genetics

Just as with humans or any other organism, some koi may just naturally grow to be larger or smaller than average. There’s not much that you can do about this – if they’re healthy, eating as much as they want, and still aren’t growing, that’s probably simply as large as their genetic code will allow them to grow without become obese or ill.

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2) Stress/Illness

Stress, most often caused in fish by overcrowding, lack of dissolved oxygen (hypoxia), hyper or hypothermia, malnutrition, excessive water salinity, illness, and contaminants and pollution, results in a host of body responses. Namely, energy that would normally go to things such as digestion, growth, mating, etc., is now going toward trying to maintain homeostasis in an unstable environment, and as such growth becomes slowed and stunted.

In addition, the stress hormone cortisol is released to help fish adjust to environmental stressors. In the short term, this is useful as it alters hormone production, metabolism, and behavior. However, if released into the system regularly, say due to overcrowding, cortisol results in things such as reduced brain function, stunted growth, and reduced ability to fight off illness and disease.

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 3) Water Temperature

Fish are ectotherms, meaning that they cannot regulate their own body temperature and must largely rely on the surrounding water to control their temperature. In warmer waters, metabolism is increased, resulting in more activity, greater appetite, and resultantly (usually) increased growth (unless, of course, the water is too warm, which then causes stress, illness, and depressed growth).

Contrastingly, colder waters result in lethargy, reduced appetite, and as such reduced growth as fish try to conserve energy. This is considered normal during the winter, as fish enter torpor. However, keeping your pond warmer even during the winter can result in greater koi growth.

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4) Water Quality

As mentioned in the section about stress and illness, ponds that have a temperature, pH, KH, salinity, or dissolved oxygen content outside of that which is considered healthy for koi will result in koi becoming stress. Stress over time results in loss of appetite, lethargy, harmful hormone fluctuations, greater chance of becoming ill, and decreased growth.

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5) Nutrition

Nutrition is one of the most key elements for optimum koi growth. A poor diet will result in stunted growth, illness, and even deformities or death. Be sure to thoroughly research any food that you’re considering giving your fish, be it pellets, freeze-dried feed mixes, or even food that you make yourself. Alternatively, you can use one of our pre-selected top koi feeds here!

A lack of protein will result in impaired growth, excessive lipids damages cellular metabolism and can lead to deadly diseases like pansteatitis, not enough lipids causes organ damage and stunted growth, and feeding too many carbohydrates results in liver degeneration.

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How to Make Koi Grow Faster & Larger (Koi Growing Tips)

The first two or three years of a koi’s life are the ones with the greatest growth and greatest potential for increased growth, so efforts to expedite and maximize growth should be heavily focused on during this time. It’s going to be infinitely more difficult to pack extra size onto an eight year old koi versus a one year old.

1) Temperature Regulation

As mentioned previously, water temperature directly influences digestion, metabolism, activity level, appetite, and the production of various hormones and chemicals necessary for proper body functioning. Do keep water temperatures within koi’s preferred range of 59 to 77° F (15 to 25° C). If possible, keep them above 65° F (18° C), as koi’s lower limit of 59° F is typically experienced during winter and results in decreased metabolism and activity, and thus decreased growth.

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2) Maximize Water Quality

When water quality is properly balanced to suit koi, they will be their healthiest, happiest selves and thus more likely to grow quickly and robustly. Keep temperatures within the range listed above, pH between 7.5 and 8.0, dissolved oxygen levels of at least 7 parts per million (though 9 ppm or above is fantastic, and below 5 ppm becomes dangerous for fish), and little to no ammonia, nitrites, or nitrates as these are known to hinder growth and can lead to various illnesses.

Water changes should be conducted once per week, in which 10 to 20% of the water should be changed out and replaced with fresh water to help remove pollutants, waste, and reduce the amount of ammonia, nitrites, and nitrates that are present in the water.

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3) Provide Quality Nutrition

For the best growth, koi should be fed a balanced diet composed of 35 to 40% protein, coming from sources, such as bloodworms, shrimpmeal, fishmeal and other aquatic sources. However, koi are also adept at processing plant based proteins, like soybeans, spirulina, and wheat germ, so these can be switched to in colder weather to help provide complex carbohydrates and fats when the fish are in periods of lower growth where proteins are less utilised.

Carbohydrates should compose only 10% or less of their diet, with lipids (fats) coming in at 5 to 10%. Excellent food sources for koi to provide their needed fiber, mineral, and carbohydrate requirements include nutritionally balanced pellets, shelled peas, spinach, citrus fruits, watermelon, broccoli greens, and raspberries.

Pellet feeds can be used  to solely provide adequate protein and nutrition without the need for supplementary foods, but we only recommend using selected brands with high quality ingredients and nutritional profiles. Our top koi feeds for growth can be found here!

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4) Don’t Overstock Koi!

A study conducted on Vietnamese koi found that overstocked ponds and tanks experienced as much as 20% less growth per fish and increased mortality. Having fish can become sort of an addiction, as it’s wonderful to watch them grow and interact, and to play around with different pond setups.

However, stick to the general rule of thumb of having only one inch of fish per one square foot of pond, and keep in mind that fish grow! So, if you’re purchasing a two inch koi fry, remember that it will likely grow to be around 20 inches or more in length by the time it reaches adulthood. Your calculations should utilize adult fish size, not the size that they are when you purchase them.

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5) Optimize Your Feeding Schedule

Keeping your koi on a set feeding schedule will help you to not only maximize their growth, but better monitor how much they’re eating and their overall health. Try to feed them three to six times per day, as koi don’t have overly efficient digestive systems so smaller meals will be easier for them to process and ensure that all necessary nutrients are being properly absorbed and utilized by the body.

Make sure that these feedings occur at the same time each day, and only feed them as much as they’ll eat within five minutes. Otherwise, koi (and other fish, for that matter) are likely to overeat due to an instinctual drive to eat as much as they can while they can in case another meal doesn’t come along for a while. Afterwards, clean out any excess food that hasn’t been eaten from the pond to ensure healthy water quality and prevent your koi from eating old food later on.

This schedule will also build trust between you and your koi, as they will come to not only recognize you but associate you with food, particularly if you stick around while they’re eating. Building trust and bonding with your koi will help them to feel safer and more comfortable, and may influence growth as it relates to mental as well as physical wellbeing.

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6) Implement Better Pond Substrate

Studies conducted on koi carp and select other domesticated commercial pond and aquarium fishes concluded greater growth rates as well as total growth when raised in ponds with natural sediment bottoms (earthen ponds) as opposed to aquariums or tanks.

This is likely because wild carp are bottom feeders, depending on natural food sources such as plant matter, aquatic macroinvertebrates, and zooplankton that are typically found in mud and dirt in the bottoms of rivers, lakes, and ponds. Though domesticated, koi are also bottom feeders and retain an instinctual desire to forage on pond bottoms for extra food.