I have had some problems with fish before. My first fish was a yellow tail damsel and that thing would not let anything eat. Had to trade it in. It was particularly aggressive towards the seahorse. It was too small to do any physical damage but the constrant harrassment must have been very stressful. I wouldnt recommend any kind of damsel. My clown and copperband are pretty chill though. The only realy danger from these two would be food competition.