Devilfish
You may recall the furor raised a few years ago over the emergence of the Northern Snakehead in the United States. Everyone went bonkers when this fish, native to China and Korea, was found in a Crofton, Maryland, pond. There are reasons for the bonkerism.
These spawns of the Devil are non-stop eaters, devouring other fish, reptiles, amphibians, small mammals - basically anything they can catch. This is not good for native specie populations. Also, they are prolific breeders and will take over a body of water in just a few generations. But the worst trait of these killing machines is that they can travel overland to another pond, lake, or river.
Snakeheads can quickly grow to three feet in length, are fast swimmers, are endowed with a mouthful of razor-sharp teeth, and have no natural predators. You can see why our native fish populations are in trouble when faced with this new threat.
Reports are trickling in about snakehead populations already established in Pennsylvania, Massachusetts, the Carolinas, Florida, and California. It won't stop with these states. Poison has been used to eradicate the fish when found in isolated ponds and small lakes, followed by restocking with native fish species. But you can see how impractical and really quite impossible it would be to poison rivers and large lakes.
It looks as though we will have to contend with yet another invasive specie that will play havoc with native denizens of our freshwater habitats. Although reportedly tasty, I don't think we'll be able to eat them out of existence.