LOL. I have a fish that thinks he's a tank. Flag-tailed prochilodus. That big bastid is about 14", dumb as hell, and likes to smash into things. He also eats a ton. Strongest fish I've ever kept, salt or freshwater. Thought maybe a bala shark to keep him company would calm him down. Nope...the two take turns scaring each other for no damned good reason, splashing water everywhere, trying to damage equipments, etc. Beautiful fish, but it'll be my last one of these.
