Mate of mine a few years ago. He lived in the centre of the village i live in, His house was surrounded by other houses, He had 2 smallish ponds with koi in some where quite large. Over the course of several weeks he found 2 of the large fish on the side of his ponds in the mornings, we suspected a cat, set a cat trap to no avail, we were coming back from lamping in the early hours one morning and a we spoked a heron from his garden, Here's another one to watch out for, i sat fishing a couple of months ago and watched a pair of crows pull 2 fish out of the commercial i was fishing.