I won 2 small percs (clowns) at a BRS meeting last year to an established tank with 2 larger ocerlaris. The other 2 bullied the new ones. One died within a month from the bullying, the other jumped out of the tank once, was forced over the overflow into the sump... but is still around now almost a year later. So from my personal expience it is a 50/50. That will really only affect clowns.
Typically in smaller tanks like a 55 you can’t get more than 1-2 of the same species. And with 55 gallons if you have any sort of rock work that impedes swimming I would stay away from Tangs (maybe a Kole eye tang if you get it small)
What is your current live stock and what are you looking to get?
Damsels can be territorial. I have a small blue one which is a model citizen and a larger black one with a white spot and he is a jerk to anything around his size.
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