The deep sea anglerfish, which comprises the suborder Ceratioidea, is one of the best-known of the weird and highly specialized creatures which inhabit the deep ocean. There are approximately 120 known species of deep sea anglerfish, all characterized by the possession of a lure, usually dangling from the chin or protruding from the forehead, which they use to attract food, and possibly sexual partners. This lure, also known as a photophore, glows in the dark due to millions of bioluminescent bacteria - this amazing adaptation, which has occurred in many deep sea creatures, ensures that the lure can be seen at depths at which no light whatsoever penetrates from the surface. The angler's skin is specially adapted not to reflect blue light, and since almost all of the light emitted from deep sea fish is blue, it remains invisible behind its lure, ready to pounce on anything that comes within range.

Deep sea anglerfish are usually quite small and round, with soft flesh and bones and small eyes, and a scary mouth which sometimes takes up the entire front of the fish. They are not the most streamlined of fish, and cannot swim very fast, and yet despite this drawback they are very active and powerful predators with strong jaws and teeth. They also have the ability to capture and digest fish up to twice their own size, due to an enormously expandable stomach.

Young deep sea anglerfish hatch from millions of eggs laid by the female, which float to the surface of the ocean to produce tiny, gelatinous fish which feed on plankton. These fish gradually begin to descend, and undergo their metamorphosis to adult form at roughly 3000 feet. Adult deep sea anglerfish have been found at depths of up to 4000 metres, but they are not typically bottom-dwellers - instead they use their layers of gelatin and the low protein content of their muscles to swim and float in the deep mid-ocean.

There is a great degree of sexual differentiation, with the females being by far the larger and more active predators - only females possess the bioluminescent lure which attracts larger prey, and male deep sea anglers usually feed on far smaller fish. An unattached male possesses no digestive tube, and will therefore eventually die of starvation, but as soon as a male and female meet and mate, the male becomes a parasitic life form, attaching itself to the female using its sharp teeth and ungergoing a startling metamorphosis. An attached male will lose its eyes and most of its internal organs, and its skin will fuse with the female's where the jaws meet her skin, leaving only a small gap for breathing. The male stops feeding itself, and is fed through blood vessels which have joined with the female. Its testes grow, and it effectively becomes a reproductive organ attached to the female for the rest of its life. It's thought that this behaviour developed due to the extreme difficulty of free-swimming males and females finding each other with any regularity in the vast, dark sea they inhabit. Apparently a female can have up to six males attached to her, all vying to fertilize her eggs.

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