Ducks, swans and geese only eat grass and pond plants, not fish. You would really only need to worry about herons, cats and if the fish are small Kingfishers, if you are lucky enough to have them in your area.
i would put the fish in its just i would have to put a net over the pond to make sure they would be safe or i would be worrying for days on end and there can't be a net over it because the ducks won't be able to get into the pond
Susie your fishes are so cute. my pond fish have a heater it goes on over night .. just let dogs out garden and all 8 of the fish are in the corner round the heater. netting over top just about about make them out!