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Anglerfish are named for their characteristic method of predation, in which involves the use of the modified first spine from the first or spinous dorsal fin. This spine (the illicium) protrudes above the fish's eyes, with a fleshy growth (the esca) at the tip of the spine (the netdevil anglerfish has similar growths protruding from its chin as well). This growth can be wiggled so as to resemble a prey animal, and thus to act as bait to lure other predators close enough for the anglerfish to devour them whole. To accomplish this, the anglerfish is able to distend both its jaw and its stomach (its bones are thin and flexible) to enormous size, allowing it to swallow prey up to twice as large as its entire body.
As most anglerfishes live mainly in the oceans' aphotic zones, where the water is too deep for sunlight to penetrate, their predation relies on the "lure" being bioluminescent (via bacterial symbiosis). In a related adaptation, anglerfish are dull gray, dark brown or black, and are thus not visible either in their own light or in that of similarly luminescent prey.
Early anglerfish researchers were puzzled when most of their newly-captured ceratioid anglerfish specimens were female. They subsequently discovered that in many ceratioid families, due to an extreme level of sexual dimorphism, the male anglerfish does not exist as a separate individual after reaching maturity.
Since their environment is lightless, anglerfish would have great difficulty in finding a mate at the right time. Therefore, the male anglerfish attaches himself permanently to the female's skin.
Some anglerfish have a unique mating method. Without light, finding a mate is a problem, especially at a time when both individuals are ready to spawn. When scientists first started capturing ceratioid anglerfishes, they noticed that all of the specimens were females. These individuals were a few inches in size and almost all of them had what appeared to be parasites attached to them. It turns out that these "parasites" were the males. When a male anglerfish is hatched, he has extremely well developed olfactory organs that detect scents in the water. He has no digestive system. His goal in life is to detect the pheromones that the female anglerfishes release. When he finds a female (and if he doesn't, he dies), he bites into her flank which releases an enzyme that digests the skin of his mouth and her body. The two then fuse together, including blood vessels. The male degenerates into nothing more than a pair of gonads that releases sperm when the female releases hormones into the bloodstream that signals she is ready to release her eggs.