It's well known Great Blue Herons and the like transfer undigested roe from "whereever else" to isolated ponds to stock them with bream, etc. I've seen evidence of it occuring time and time again on farm ponds and private lakes with no feeder streams, so I doubt it's a myth. Will these fish carry any levels of mercury or PCB's once they're eating size? (Assuming the water and rain is unpolluted, of course)