Before I gave alway all of the cichlids I had (I discovered rare and oddball fish!) There was an oscar that was atleast 3 times as big as all the other fish in its tank but was a total pus and would back off to all of the other fish. It would lock lips once in a while but would always back down even though it could eat the others! It got so picked on that its color changed to almost pure black all the time. Ive got a big oscar though that wont even back down to me. Its amazing how diverse these fish can be.