Anglerfish are one the most bizarre-looking fish that dwell in the pelagic and benthic zones of the ocean. They belong to the order Lophiiformes. Some families of this order live in the deep sea, while a few dwell in shallow water. The scientific name of the deep sea anglerfish is Melanocetus johnsonii.
The fish got its name from its unique mode of predation. It possesses a fleshy growth that sprouts from the middle of its head. This outgrowth resembles a fishing pole, and is used as a lure for attracting prey. This is considered somewhat similar to the act of angling, and so the name 'anglerfish'. About 200 species of anglerfish can be found in the oceans across the world.
The deep sea anglerfish has a ferocious and somewhat grotesque look, though it's not very big in size. This ugly fish has earned the name of 'common black devil' due to its unsightly appearance. What gives the fish its terrible look is its large mouth with the sharp, fang-like teeth. The teeth of the anglerfish can look more intimidating than those of the sharks. This ugly fish has a round body that looks like a basketball. The female fish can reach a length of about 20 cm, while the male is quite small and it hardly grows to a length of about 3 cm.
The body of this fish can be dark gray, brown, or black in color, and its skin can reflect blue light. This in turn, helps the fish remain invisible to other deep sea animals, as almost all bioluminescent fish or creatures of the deep sea emit blue light.
The fish possesses one or more long filaments that sprung from the center of its head. These are the modified spines of the anterior dorsal fin, but they look like filaments. Usually, the longest filament is the first spine or illicium that protrudes above the eyes, and then terminates in an irregular mass of flesh at the tip of the spine, which is called 'esca'. It basically serves as a lure that can be moved back and forth in all directions. The spine attached to this filament-like growth is also movable.
As has been mentioned already, this fish has an extraordinary mode of predation. It basically uses its lure or the longest filament to attract its prey. The fish basically catches its prey with the help of the light emitted from the esca. This bioluminescence is the result of a large number of bacteria that enter the esca, and produce a bluish or greenish light. While remaining motionless, the fish waves its lure back and forth, and waits for the prey to come closer to its mouth.
The specialized spine attached to the lure can also be moved by the fish in any direction. Moreover, the 'esca' is connected with the mouth reflex, so that when the prey touches it, the fish can instantly snap the prey with its powerful jaw and then swallow it. The teeth of this fish are bent inwards, for which the prey cannot escape once it enters the mouth. The anglerfish can swallow a prey about twice the size of its body, as it has the ability to distend its jaw and stomach to an incredible size. This unique ability can be attributed to its thin and flexible bones.
The anglerfish exhibits a unique and bizarre mode of reproduction. The male fish is much smaller than the female, and looks quite different. The male is usually not larger the size of a small finger. It is black in color, and it possesses well-developed olfactory organs at birth, with the help of which it can detect the scent of the female in water. Due to its small size, the male cannot effectively find food in the deep sea, and moreover, its digestive system starts to degenerate once it attains sexual maturity.
All these factors make the male fish desperate to find a female and mate. It can detect the pheromones of the female fish with the help of its highly-sensitive olfactory organs. When the male finds a female, it attaches itself to her body with its small hook-like teeth. The male then bites into the skin of the female, and releases an enzyme that dissolves the skin of its mouth. The enzyme also dissolves the skin of her body, and then both the fish fuse together to the level of the blood vessels.
The male then slowly loses all its body parts, except for the pair of gonads. These gonads release sperms when the female is ready to release the eggs. The male thus remain attached to the female and draws nourishment from her body, just like a parasite. The female fish can carry up to six males in this way. This bizarre method of reproduction makes sure that when the female is ready to spawn, she does not have to look for a male, as he is already available.
After fertilization, the female lays eggs in a thin, transparent and gelatinous sheet, which can be 2 to 3 feet wide and about 25 to 30 feet long. This egg sheet floats in water, till the eggs hatch into larvae. The larvae usually feed on the surface of the sea, until they mature.
So, the deep sea anglerfish is really a unique fish, not only from the way it looks and hunts its prey, but also the way it reproduces. This exceptional method of reproduction was discovered when scientists noticed that all the anglerfish they captured were females, and almost all them were found to have parasites attached to them. Later, they were able to figure out that what seemed parasites to them were actually the remains of male anglerfish. Subsequently, they unveiled this unique mode of reproduction.