Is a Snakehead (Channa spp.) scarier than Knotweed? Judge for yourself by watching the new Sci-Fi original movie, "Snakehead Terror." Featuring Bruce Boxleitner (who's obviously killing time waiting around for a decent B5 spinoff...or maybe that's me :-), the movie is about the terror imparted on a small town by a mutated snakehead fish. You can read the IMDB entry here. For something a bit more realistic, you might want to check out "Swarm of the Snakehead," featured in an ISW post last year.
Thanks to a member of the ALIENS-L listserver for posting a link to the story.