When a lake freezes, fish survive by changing their metabolism, which lessens the amount of food and oxygen that they need. Without this adaptation, fish would not survive the icy winters.
Although fish can survive when a lake or pond freezes over, they cannot survive indefinitely. Most fish can survive for a few months at the most. In addition to the slowing metabolism, the fish know when the winter is coming, so in the fall they start to eat as much food as they can. The food is then stored inside of the fish's body so they do not require additional food until the spring.