My harlequin went for the new ones and he was one of the first ones in my tank. I think after it accidentally ate my Bangaii Cardinal (who was there before him) he thought it was okay to eat small, newer additions. My first fish in the tank were a pair of small clowns and he never bothered them.
I do careful research before any fish purchases and at the time I never found anything on the net suggesting Harlequin tuskfish ate any fish in captivity. Inverts like snails and shrimp, yes, but not fish. And it is true as someone mentioned above they will tear up any rockwork light enough that they can fit in their mouth. I witnessed it a few times looking for a blenny in the rockwork (which disappeared btw, maybe he ate him too?) and moving rocks with his teeth. pretty cool to watch but I knew I had to take him out of there before it totally alters the rockwork and eat all my small fish:strange:
