Birds that fish ponds will bring in eggs on their feet. Turtles will also bring them in.
One word... herons. If you see them, you can count on having hundreds of fish within 2-3 years. Trust me, I have seen it in my pond.
I threw 2 fish (different species) in their when I first built it. Two years later when I pumped it out to do a major overhaul I had hundreds of fish in there.
Everytime I saw that blue heron trying to fish my pond with only 2 fish I put in there it made me laugh. Little did I know he introduced a number of different species into the pond and created his own private fishing hole.
