Mystery solved.Too funny! we have a 90GaL and our pond fish bred a few years ago, oddly enough the ducks rarely visit the pond it's right in front of our house so probably too loud, they do on occasion take a quicky bath but never bothered the fish, thankfully nor touched the frogs there(tons of them too)
You actually got me thinking, we had a HUGE frog last year and my new Koi magically disappeared the fish winter in the house.. we never saw him float but never found him... hmmmmm