Fish don't hibernate persay, but they use other instinctual tactics to survive the period of cold temperatures and lack of food. Rather than hibernating, fish enter a period of dormancy during the wintertime. This reduces their metabolism and slows down their activity. This means fish are using less calories and preserving their energy until food stores become available again.
In nature, fish's instincts tell them to begin entering their dormant period as they feel the temperature get colder and access to food becomes less available. To simulate this, you'll want to reduce the frequency of their feedings as it gets closer to wintertime. Take frequent temperature checks of your pond as it gets later into fall. Once the water temperature drops to between 70 and 50 degrees, begin spacing out your feeding times further and further until it drops below 50 degrees. At this point, you can stop feeding your fish entirely until temperatures rise again.
