The U.S. Fisheries and Wildlife Service is considering banning the importation of the Black carp (Mylopharyngodon piceus), according to this article from the Environment News Service. The carp were first introduced from Asia in the 1970s, both as a food source and as a biocontrol for snail and insect populations. Now the fish are considered to pose a danger to native snails and mussels, and there is a concern that they will escape from fish farms into nearby rivers. Here's a link to an older article reporting on the public outcry resulting from the proposed release of black carp to fight parasite-carrying snails in Missouri catfish farms.