get a Red Devil. VERY aggressive. One fish tank. meaning he'll kill pretty much anything else you put with him. Get around 12. Sometimes more.
Attack the glass, and rearange your tank. Very good personalities.
My O eats any feeder fish I put in there in less than a second. He ate three dozen in less than 12 hours once. I don't feed him live food anymore, but my roommate throws a goldfish in there every now and then. an Oscar is good in a 55 for about a year (maybe less).