That's interesting FT. How far did the fish have to swim to get into your pond? Downstream from my pond is a tiny seasonal drain and the closest year round water is probably about 1/2 mile away. I have no doubt that what you say is true, but if I'm lucky I'll have a while before other species can enter my pond that way.

Mr H's small pond which is the FH/RES/WM pond is even safer than mine against migration of outside fish because they would have to pass through mine first.

I'm sure you all can appreciate how I feel now that there are 100 baby Shellcrackers cruising my pond in search of food. \:\)