Since fish require oxygen to survive, aerators are often added to fish ponds to provide extra oxygen in the water during the wintertime. The amount of ice on the water's surface is also sometimes reduced so that theres more contact between the water and the open air. This is done through the use of heaters or de-icers.
If you see a number of fish gathering around the holes you've made in the ice, this means that they aren't being able to breathe well. You'll need to add more oxygen into your water through the use of aerators or making more holes. Never manually make holes in your ice by hitting or smashing! The vibrations this causes in the water can be deadly to fish.
