MarkECIN, we did discuss birds moving adult fish to other ponds. Here's my view:

 Originally Posted By: GW
I don't doubt that mature fish are dropped by birds occasionally, but mystery fish show up in ponds far too often for that to be the main explanation.

1. What are the odds that a dropped fish will land in a pond?

(Statistically it is far far more likely to hit dry land, but let's say it hits a pond.)

2. What are the odds of the fish surviving capture, transportation without oxygen and the long drop into the pond?

(Let's say a fish did land in a pond and survive the ordeal.)

3. What are the odds that another fish of the same species will also land in that very same pond and survive?

(Okay, assume that this event happened twice in the same pond.)

4. What are the odds that the second lucky fish is the opposite sex of the first lucky surviver?

(Easy, the odds are 2 to 1, so double the odds against the fish successfully establishing.)

With each of those four steps the odds get higher and higher that the dropped fish won't survive and establish themselves. I believe the "dropped fish theory" can't account for even a tiny fraction of the mystery fish that appear in ponds. I'm more inclined to believe that birds are seeding ponds intentionally.