Fishes metabolism alters with the pond water temperature, so does the nutrient requirment of the fish. If the temperature drops and the fishes metabolism slows down then any food left in their digestive system will remain there and could start to literally rot inside them. Feeding fish during the winter months can therefore be a very tricky business. If you choose to feed your fish you must be confident that the water temperature will remain suitably warm enough for several days. You should use wheatgerm foods, which are specifically designed to meet the fishes requirements at this time of year. If you are in any doubt it is better not to feed.