Plan to stop feeding your fish once the water temperature drops below 50 degrees F. Some pondkeepers will recommend a change to cold weather food at this point, which can be digested more quickly. However, when the water temperature hits 50 degrees, the metabolisms of cold hardy fish will have already started to slow down, and at 40 degrees the fish will entor semi-hibernation. It can be deadly to fish if they still have undigested food in the stomach over their period of semi-hibernation, so it's safer to stop feeding altogether at the 50 degree mark.
Even if you see your fish up and moving during the winter, don't feed them yet! Fish are cold-water creatures and they cannot maintain a normal metabolism in cold conditions, so any food entering their system will remain there, potentially harming or even killing your fish. Don't worry - cold water fish have evolved this response to deal with cold and they're prepared to handle it. Fish that are healthy entering into the winter won't starve before it warms up again.
