Koi fish, a Japanese carp used in large ornamental pounds and outdoor water gardens for its large size and attractive colors, is becoming a popular choice for koi aquaponics systems. They’re sought out for their durability as they can withstand year round temperatures and are highly resistant to common parasites. Whereas the most used aquaponics fish, the Tilapia, need temperatures above 75 degrees to thrive, Koi can function in temperatures ranging from 35 to 85 degrees. This means less energy is needed for heating the pound so energy costs are lower. They’re great algae eaters so typically subsist on existing growth within the aquaponics system in addition to greens such as peas, watermelon, and lettuce. During winter they require less frequent feeding (once a day) and produce less waste whereas in warmer temperatures it is recommended they are fed several small meals throughout the day and they subsequently produce more waste. As cold water holds more oxygen, it’s important to add oxygen in the warmer months to ensure the health and functioning of your Koi.
Koi are not considered a good fish for eating so for those looking to garner not only plants from their aquaponics system but also a protein source might be better off with a different fish such as Trout or Tilapia. However, Koi can reach lengths of up to two feet after four or five years if water quality and space in the tank are optimized, meaning their resale to hobbyists and pet stores may reap a profit. One of the challenges in this regard is that after a few generations, if selective breeding is not employed, the pretty sheen and color array will fade making the Koi look no better than common carp. Thus, the resale value will be diminished if their breeding is not managed properly. Another drawback is that when the Koi get larger they start to produce a lot of waste and can overload the system. The waste production must be monitored and a larger and more efficient filter may need to be installed.
As a final thought, Koi have been known to live up to thirty years and grow longer than two feet. As they grow larger more space will be required for them to thrive. Having several large Koi would require a tank ten feet in depth and over 1000 gallons of water. Considering this, it can be a great option for a koi aquaponics system for a few years as they grow from small fish to large and colorful ornamental fish, but when they get too big and start producing a lot of waste it may be time to swap the larger ones out for smaller ones.