Only the male humphead wrasses have a hump. The hump is a sexual dimorphic trait — the hallmark hump is not found in female fish. Marine biologists believe that the size and the shape of the hump signals the genetic qualities of the male. The function of the hump is compared to that of the antlers, horns and tusks, with one exception — they are never used for fight. The older the fish, the more prominent its hump. In addition, as the male fish ages, its hump assumes a brilliant blue color.