I have a few different kinds of damsels and they do fight (my yellow one is queen of the tank and extremely territorial), but the fighting hasn't been physical... they kind of just grunt (it's loud!) at each other and shake their tails. Once I had three blue damsels and two of them paired up on the one and killed him. That's the only major trouble I've ever experienced. I like them because they're hardy fish and colorful, too.