Fish's metabolism slows greatly during the winter months, meaning that they can no longer properly digest food until things warm back up. It's better to err on the side of caution, and resist feeding your fish during these winter months, as eating while their digestion is slowed down can be harmful. Even if the weather should temporarily warm up and your fish become more active, don’t give in to temptation. This willl only restart their metabolic system, and make it harder for them to survive the coming winter months.
The kind of hibernation fish enter during the winter is known as torpor, and is the same kind of hibernation that bears enter. During this time, the animals are at a reduced level of energy and conciousness to preserve energy and warmth, but they still sometimes wake up or move around. You'll sometimes see your fish up and moving around during the winter. Don't worry, and don't feed them! They are just stretching their fins, but will return to their kind of hibernation shortly.
