Angler fish reproduce via spawning between the large, predatory female and the small, parasitic male. Male angler fish attach to a female and remain there for the duration of their lives.
Angler fish inhabit the ocean's midnight zone at depths of 3,000 feet. Little to no light penetrates this deep into the ocean. Many animals in this habitat, including angler fish, produce bioluminescence. Female angler fish have a bulbous, luminescent antenna that attracts prey. The enormous jaws and stomach of a female angler fish allow her to swallow prey nearly twice her size.
The male angler fish is much smaller than the female. Upon reaching maturity, his digestive system degenerates and he finds a female upon which to attach. His skin, jaws and eyes dissolve and fuse to the female over time. Their circulatory systems fuse, as well, and the male lives as a sort of parasite, gaining nourishment from the female. His testes remain intact for spawning.
The relationship is more symbiotic than parasitic, as the male gains nourishment and the female does not need to locate a mate for spawning - an excellent adaptation in the lightless ocean depths. Female angler fish often carry six or more males attached to their bodies. The ability to accommodate multiple males ensures greater genetic diversity for her offspring.