Diving Deep: the Anglerfish

The Anglerfish, to some, is a true deep-sea nightmare–and not just to Marlin and Dory on their search for Nemo! This species was discovered in 1833 by an English naturalist named James Yate Johnson. At the time of discovery, not much was known about the ecology and lifestyle of this ghoulish fish, as the only details came from deceased specimens. Whereas in recent years deep-sea divers have added much to our compendium of anglerfish, much of their lifestyle is still shrouded in mystery. There are over 200 species of anglerfish extant today, varying in lifestyle and size, but they all have one thing in common: an elongated cranial spine tipped with a bioluminescent organ. 

Most anglerfish live in the bathypelagic region of the open ocean—in other words, they live in the deep, dark, and cold regions, about 2000 m (6600 ft) below the surface. In complete absence of light with scarce food in the ocean depths, these ambush predators evolved their own ways to hunt and survive—by underwater fishing! The anglerfish uses its modified cranial spine to imitate other organisms in the darkness, with the photophore at the tip using a process of bioluminescence to create a blue-green light to lure in other small marine animals. Once a prey fish is in adequate range, the anglerfish will use its powerful jaws to suck in its meal whole. Though some anglerfish can reach up to four feet long and 110 pounds, most are fairly small. Despite this stature, members of this species are known to be able to swallow prey twice their size.

Museum specimen of an Anglerfish, genus Acentrophryn; image taken by Hongseok Kim in Seoul, South Korea.
Museum specimen of an Anglerfish, genus Ceratias; image taken by Hongseok Kim in Seoul, South Korea.

The bizarre appearance and predation style of anglerfish aren’t the only factors that make these fish so interesting. In fact, one of the most fascinating and unusual practices of some anglerfish species is their disturbing mating habit! For around 90 years after the first anglerfish was discovered, scientists and researchers were baffled as the only anglerfish they were finding were all females. That’s right, every anglerfish with a lure is female! These females were sometimes found with small growth like fish attached to their bellies and were believed to be their offspring. The behavior and ecology of male anglerfish were a total mystery until 1924 when Charles Tate Regan dissected a smaller, attached fish on a female and discovered they were neither growths nor offspring, but the female’s mate! 

Male anglerfish are substantially smaller than females, only about one inch long, and lack lures, large maws, and the frightening teeth of their female counterparts. Since males are not equipped for survival on their own, they spend their lives seeking out a female mate— and mate they do. Male anglerfish have small hook teeth that they use to latch onto a female’s body. Once attached, the male anglerfish releases an enzyme that dissolves the membranes of his mouth and her skin so that their bodies can fuse together, blood vessels and all! The male will lose the body parts no longer necessary to him, including eyes, fins, and sometimes even his own internal organs. He is then entirely dependent on the female for nutrition and survival and essentially becomes a fleshy lump, ready to release sperm into the water when his mate chooses to release eggs for fertilization. Even more fascinating, a female can carry up to six males at one time!

Not every species of male anglerfish is destined to such a dark fate, but this seemingly parasitic form of reproduction sure does sound like the stuff of science fiction. So, if you’re ever feeling down in the dumps about your love life, just remember: at least you’re not an anglerfish! 

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