When the water temperature of your pond drops below 55 degrees, you should stop feeding your koi.

Other fish can digest food in cold water, while koi cannot. There are a few foods that can be fed below 55, such as cheerios and some greens like spinach and lettuce, but these should only be fed during that transitional period when days are still above 55, but the nights dip into the 40s.

Do not begin feeding your fish until the reverse happens in spring--when water temps rise above 50 and air temperature maintains it. Your fish will not have much of an appetite at this time, anyway, and if you feed them in cold water, the food will sit in their bellies and rot, either killing them, or causing diseases like intestinal parasites. Disease which will most likely kill them in the Spring. Don't worry about your fish starving, or even being hungry. Koi have been hibernating like this for centuries. Visit one of our pond suppliers for foods that are ok for spring and fall feeding.

see also Cheerios