Qube said:Appears to be a long-horned cow fish. They get big!
Beengirl said:Cowfish are very cool looking. But they get about 16" fully grown and release a toxin when stressed that will wipe out all the fish in your tank.
Tony Gill said:It's a bit hard to tell from the photos, but it is probably Tetrasomus gibbosus - humpback turretfish. If so, at around 8 inches it doesn't get quite as big as the usual longhorn cowfish (Lactoria cornuta), but you still have the same problem with toxin (ostracitoxin).
Tony