Well, our happy expectations of duckweed & waterfern carpeting the top of our nice new goldfish pond have been dashed - the little beggars (fish) scoffed the lot! We've restocked with weed from the old pond but somehow I suspect we might be doing that for a while.
Which shows how ignorant I am about goldfish, really. Back at the old house we were removing great handfuls of weed from the top of the pond, pretty much every second day. (The pumpkins grew very well on this.) Same fish, same amount of commercial goldfish food every day. The only difference I can think of is the lack of any real functioning ecosystem, in the sense that until all sorts of invertebrate life colonises the new pond, there isn't anything other than the weed to supplement our feedings if the fish get peckish between meals. So maybe we'll just have to feed them more... And keep some weed growing in a separate bucket, as this goldfish afficionado suggests.
I should have looked into it more deeply, really, as it seems that goldfish adore duckweed... (Which just goes to show that data trump personal anecdote every time!)