So there are no bugs. You need plants which are so pretty, we have water lilies and others to use the nitrogen waste. You just leave the fish in the pond during the winter. They go dormant which means they don't need to be fed. You need to keep hole in the ice to release the methane gas though.
Some people use heaters .
We don't we just chop the ice. My family and I love to sit by the pond and watch the fish . It is so peaceful a place . I love to read there. If you have always dreamed of a pond put one it is so easy my Mom and I put ours in from digging the hole to building the water fall.