When I go fishing up in Sussex at the bait shops and ranger stations, they have a little magazine NJ fish and wildlife or something like that, and they list snakeheads as an invasive species and if you catch one to kill it, don't release it back. (I think they advise if you catch one kill it and call the game warden to report where you caught it and stuff.)
Biologists believe their invasion started when a man bought two live snakheads from Chinatown to make a soup for his ill sister, when she recovered he released them into a local lake.
"Snakeheads can breathe air and survive for up to four days out of water, and can survive for longer periods of time when burrowed in the mud. They are capable of traveling over land to new bodies of water by wriggling their bodies over the ground."
Very harmful to our ecosystem, but IMO very fascinating creatures.
http://www.csa.com/discoveryguides/snakehead/overview.php