I've had some aggresive fish, but the "flying dragon" Flowerhorn takes the cake. I had a Wolf fish in my tank (265G) for about three or four months... he was about 7". I added that Flowerhorn (7") and he started attcking all of the other cichlids, Freddy, Red Devil, Jack Dempsey, Jaguar and a few others, who were all between 5" - 8". Up until this point all the fish kept their distance from the wolf. Not anymore... The Flowerhorn, after beating up all the other fish attacked the wolf!!! I came home from Home Depot to find my $100 Flowerhorn all diced up on the second day I owned him!!! Most fish would have gave up, but that darn Flowerhorn kept trying to fight the wolf until I removed him. He would have fought to the death!!!