We have 2 in our 55, a 4-Stripe and a Yellow Tail. The 4-s used to think he was king of everything until he messed with the Clarkii. She taught him a lesson or 2 and now he's as peaceful as a lamb and the Y-tail followed suit. On the other hand, the Blue Damsel (Fiji Blue Devil, an appropriate name) wanted the whole 55 to himself. He now lives by himself with a CBS and duster in a small tank upstairs. Just couldnt bear getting rid of him (or the others) since they were our first. Just sentimental I guess, but its a personal decision. If you want to get the damsel out, try to trade it in. Killing is not our hobby, at least give it a chance. Not trying to be preachy, but these are lives we have decide to care for--you wouldnt do it to dog or cat, would you?