Koi will live to be over 200 years old in exceptional circumstances, however, average lifespan tends to be around 25 to 35 years.
Maximum length is a little over 3 feet. Koi can reach 18” to 20” inches in 3 to 4 years under the right conditions. They will usually only grow to the size of their pond.
Koi can be fed four or five times a day in midsummer, tapering down to once a week by early winter. They can easily go 10 days or more without being fed anytime of the year. They do not need to be fed at all during the winter.
For healthy koi and a healthy pond, the water should be constantly filtered and aerated. We recommend the complete volume of the pond be run through the filter at least once per hour.
The selling price of koi is determined not just by size, but by origin (Japanese or domestic) and by body shape, color, and pattern.
Koi can withstand a wide range of temperatures, but sudden temperature changes are not good for them. They can easily survive under ice in a frozen pond, but care should be taken not to break the ice in such a way that it transmits the shock to the koi. Koi will go dormant at low temperatures and stay almost motionless at the bottom of the pond.
Some fish will just inexplicably die, but overall, koi are remarkably hardy and healthy fish; much more so than goldfish or tropical fish. Chlorine or chloramines in city water or windblown insecticides are the biggest dangers to koi, along with predators. Smaller koi have a much higher mortality rate than larger ones, and are more susceptible to disease and changes in the environment.
Koi get along well with most other pond fish, especially goldfish, golden orfes and mosquito fish. Large catfish (12” to 18”) will eat small koi (3” to 5”).
Koi must be at least 3 to 4 years old and about 10” or longer to spawn. A single female may lay thousands of eggs at a time. The eggs hatch in about 3 to 7 days and can be removed to a different location so they won’t get eaten. The survival rate is usually much less than 50%. At two inches or so they can usually go back into a large pond.