Understanding Color-Changing Koi Fish

Published on April 28, 2022

Koi, or nishikigoi, are known as living jewels. In Japanese, koi means love or affection. What makes them so special? Koi are smart fish with brilliant colors, body confirmation and personality. They can be fed out of your hand. They are so mesmerizing that people keep coming back to check on them.

Feeding them is easy. Caring for them is easier. Loving them is easiest.

Nishikigoi were originally used as a way to consistently feed the people in the Niigata region of Japan over winter. The black koi, or magoi, was the primary color until a vibrantly colored koi was born and then bred. These beautiful fish were noticed, appreciated and ultimately bred to enhance the color and design of the koi we appreciate today.

There are indications that some koi have lived as long as 241 years; the average lifespan is approximately 60 years. There are several factors that make up how long a fish can live. The primary indicator is water quality.

Koi of a Different Color

In Japan, there are reliable breeding pairs of fish that, when bred, produce a known type of fish. Unfortunately, there are always strays that don’t give the desired color combinations. That is why the better breeders constantly scrutinize each fish during each stage of growth, starting with the smallest. Many well-known Japanese breeders have told me they would rather have a few great-quality fish as opposed to having many lower-quality fish with so-so color saturation or body confirmation.

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Genetics and water quality can cause variations in the koi colors. Variations in minerals from one breeder site to another can also affect the colors and markings of the koi. We recently received a shipment of beautiful fish from a farm with much softer water than we have. Because of this, these koi have changed their markings up to five times over three years. 

Our hard water contains calcium and magnesium, which make gray colors saturate and render deeper black colors, fading out the rice-white color. Conversely, if the water is run through a reverse-osmosis filter to take out the calcium and magnesium, the blacks can go gray, with the white turning more rice-white.

Koi Color Wheel

If you’re looking for certain color and pattern combinations, it is better to purchase fish that are more than three years old. There can ultimately be more than 200 different color combinations. The base colors start from black, white, yellow, orange and red. Convert these colors to the koi name, and you get magoi for black, utsuri for white, ki for yellow, and hi for orange or red. 

Combine these colors to get many different color descriptors that define the fish. For example, a shiro utsuri is a white and black fish. A hi utsuri is orange or red fish with black markings. A ki utsuri is a yellow fish with black markings. 

Combine three colors and get even more definitions. A sanke fish has black, red and white, where the black is located above the midline. A showa is a black, red and white fish with black markings below the midline. 

The Test of Time

There are indications that some koi have lived as long as 241 years; the average lifespan is approximately 60 years. There are several factors that make up how long a fish can live. The primary indicator is water quality. Cleaner water with a higher oxidative reduction potential (ORP) will keep fish alive longer than water that has a low or negative ORP. However, many koi live decades with muddy water that has less-than-ideal water quality parameters. External factors such as parasites and bacteria infestations can always take their toll on a population, along with birds of prey such as herons.

As koi age, you can keep their colors vibrant by feeding them better-quality fish food with high protein, which is most beneficial to keeping the fish healthy. 

We also add to their diet a variety of fruits and vegetables all year long. Koi are much like humans in that they like certain foods and not others. Common fruits we feed our fish include oranges, green peas, watermelon, limes, better grades of lettuce and any fresh fruit or vegetable in season. Better grades of fish food are generally small, brown, round pieces. The ingredients should not have a preponderance of flour as their main ingredient, but rather higher concentrations of fish meal.

Koi are easy to grow, easy to care for and relaxing to watch. Their value increases over time with their size and color. Keeping them healthy with good food and pristine water conditions will keep them alive and vibrant for many years to come.

Mark Gibson is a lifelong horticulturist and co-owner of Green Thumb Garden Center.

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