I don't have an answer to any of the questions posted or even any suggestions but think about this. All of the primary species listed are extremely hardy: catfish, greenies. These fish are survivors. When the going gets tough there the last to be gone. So whether its in the form of birds transplanting eggs or regurgitating the fish itself, who knows. They could have swim upstream, or maybe even underground springs that no one else knows about. I think most of the time nature is more in control than we realize.
Chris
