Snakes heads have also become a game fish in parts of the mississippi river valley, and of course there was the huge issue with the walking catfish over much of the south, and even heard a story about ptenopoma being an issue somewhere, Here in California of course if they think it could be a problem they just ban it, Clawed frogs, any kind of piranha, ferrets etc.... all banned in california. In Florida also they have banned many kinds of fish except for aquaculture purposes along with many species of aquatic plants, Water Hyacinths come to mind as does hyrgophilia.

Wild populations are wide spread, does seem to make sense how some species survive where they shouldn't, but some how they do, In colorado for a while they were considering banning piranha because some kid in broomfiled CO pulled a very large one out of a local pond, When they seined the pond they found that there were other piranha in the same pond, but it was isolated and the pond had no drainage so it didn't spread, Generally I would say that the spread of non-native fish species such as oscars and what not is probably due to someone having fish they wanted to get rid of and carelessly dumping them where they shouldn't have.