This may sound like a silly question, but do ducks eat goldfish?

I had two (a matins pail, I think) ducks visit our yard this afternoon.
They dined for a while on the droppings from my bird feeders. then they
spotted my pond and decided to take a swim. They dived down but I didn't
see them come up with any fish. The pond has about 20 gold fish and its a
regular preform about 18 inches deep.

I enjoyed watching the ducks but don't want them eating my fish. Should I
encourage them to stop by or scare them away? They didn't seem to scared on
my 100 lb dog who found them to be a curiosity. They didn't fly away until
he got about 15 feet away.

Any comments?

Thanks.

Tom in Howell, NJ