The humpback anglerfish or common black devil, Melanocetus johnsonii, is a deep-sea anglerfish in the family Melanocetidae, found in tropical to temperate parts of all oceans at depths of up to 2,000 meters (6,600 feet). Its length is up to 3 centimeters (1.2 inches) for males and up to 20 centimeters (8 inches) for females.
Male humpback angler fish are much smaller than the females, being no more than 3 cm (just over an inch) long, whereas the female typically reaches 18 cm (7 inches) in length. Hump back angler fish remain free swimming into adulthood, which is not the case with other deep sea anglerfish: with these, males swim freely when young, but before reaching adulthood the male will fix itself permanently to the rear of the female's body, living thereafter as a parasite of the female. The male's internal organs now atrophy as the fish shares the female's blood and becomes simply a sperm provider as required.