My uncle has two arapaima gigas fish.
Dont ask me how he got them, because the fish is not supposed to be traded internationally (from Brazil to Indonesia). He housed them in a huge aquarium.
He also has a few of "fishzilla" (
http://en.wikipedia.org/wiki/Snakehead_%28fish%29 ).
Those fish are from hell, I'd say.
One of them jumped really fast and high out of the aquarium and was an inch from taking a chunk off my face (Im not exaggerating) when i was viewing them over the aquarium. They even ate their kind, live, but only from waist to tail, leaving head and belly. really disgusting and very disturbing.