I remember my brother had a 6" wolf fish. It would just sit on the bottom of the tank all day and if we put anything in the tank, no matter the size, it would devour it whole. It ate a 4" red devil, 5" Oscar, and many other things, it never left anything. It even bit my mom pretty badly when she put her hand in the tank to clean once. Def the meanest and most aggresive fish we've ever owned, just a very boring fish though.
Joe