Bruce,
That's a good point but natural hybridization is quite common among sunfish. Fish producers are very careful to drain and lime to make sure there are no other sunfish before a pond is filled up and broodstock are added.
Of course this is just my opinion but I think there is SOME bluegill in that fish. The mouth doesn't appear as large as a true green sunfish and the body shape reminds me more of a bluegill. Could be wrong though. It's happened before!
