+1 Zissou...could be ich from the stress of being in a new tank. What size is the tank? Is anyone picking on him? If it is ich, you can try to treat in a qt tank w/ copper or hypo salinity, but as soon as you put him back, he'll get ich again, since you already introduced it with this fish. If you don't want to qt the fish, you can just hope he fights it himself.