Here's some ways to keep a hole in the pond ice. Gases need to be exchanged so fish can survive.
On to the de-icing ideas:
Carolyn hooks up a hose to an inside tap and runs water over the ice. She has a dechlorinating device hooked to the hose.
Craig floats a flat black painted can wrapped in styrofoam to keep it from sinking. The black paint absorbs warmth and keeps a hole open in the ice.
I have used a milk jug with a rope tied to it and with a couple of cup of water in it so it stays in the water.
Or you can buy a de-icer that keeps a hole open.