Old illustration of an anglerfish
Image credit: from the “Report on the deep-sea fishes collected by H.M.S. Challenger during the years 1873-1876” by Günther, Albert C. L. G. (Albert Carl Ludwig Gotthilf)

Dive far enough down into the ocean, and you’ll reach a place devoid of light but full of organisms known for their extraordinary adaptations to this extreme environment. Many, for example, lack eyes or have slimy skin. It is here where you will encounter such creatures as the elusive giant squid, bright red giant tubeworms, and goblin sharks. Perhaps the most fascinating of these creatures, with its fishing pole appendage and bioluminescence, is the anglerfish.

Anglerfish belong to the order Lophiiformes, a highly diverse group of marine fishes with a wide range of body forms ranging from globose to spherical or even elongated to compressed. The heads of these animals are quite large; they houses the fish’s enormous eyes and terrifying mouth, which contains rows filled with numerous small teeth. Their coloration ranges from unmarked gray, brown, or black to multicolored complex patterns. They are distributed throughout all oceans and major seas of the world. Most are benthic as adults, typically occupying depths that range from the surface down to approximately 650 ft (200 m), with a few species extending down even further, living up to 8,200 ft (2,500 m) beneath the surface or more.

The most well-known identifying characteristic of the anglerfish, which inspires its common name, is its fishing rod-like appendage, known as an illicium. Used to lure prey out of the dark so it can strike it with its razor-toothed jaws, the illicium is an extension of the forehead, which evolved from the spines of the fish’s dorsal fin. The end of the structure has an organ that glows to entice potential prey living in the darkest regions of the ocean. Some species also have luminous tendrils that look like seaweed trailing from their chins, which are also used to attract prey.

Some species make their own glowing lure themselves, while others form a symbiotic relationship with luminescent bacteria, with most using an enzyme called luciferase to produce the glow. To attract prey, the fish floats passively while wiggling its rod until prey approaches; this creature then uses its powerful teeth to clamp down on its unsuspecting victim. Beyond attracting prey, the luminescence also attracts mates and wards off predators.

The unique qualities of the anglerfish don’t stop at its ability to glow, however. Behind the base of their pectoral fin, they also have pore-like gill openings that can not only help capture prey but can also help them move. Some even possess the unique ability to use their pectoral fin to prop up their bodies and “walk”!

A striped anglerfish against a bright blue background
Striped anglerfish (Antennarius striatus). Image credit: SEFSC Pascagoula Laboratory; Collection of Brandi Noble, NOAA/NMFS/SEFSC.

How many species of anglerfish are there?

There are roughly 321 extant species of anglerfish, such as the wolf-trap anglerfish and triplewart seadevil.

How much does an anglerfish weigh? How big is an anglerfish?

Their size ranges from three feet in length to less than a foot, with males being much smaller than females. The largest can weigh almost 60 lbs (27 kg)!

An anglerfish off the coast of New Zealand
Image courtesy of New Zealand-American Submarine Ring of Fire 2005 Exploration, NOAA Vents Program.

How do anglerfish reproduce?

In addition to their amazing feeding adaptations, some anglerfish continue to amaze scientists with their bizarre method of reproduction. Some species exhibit a behavior knows as sexual parasitism. Instead of having to continually look for a female in the vast abyss of the ocean, the male has evolved to fuse with a viable partner. When a young, free-swimming male finds a female, he latches on with his sharp teeth. Over time, the male physically fuses with the female, connecting to her skin and bloodstream while losing his eyes and all his internal organs, except for the testes. Females have been found to carry six or more males on their bodies.

What other feeding adaptations do anglerfish have?

When an anglerfish opens its jaws to swallow its prey, it creates suction that pulls the victim inside. University of Washington scientists David B. Grobecker and Theodore W. Pietsch have recorded one engulfing its prey in less than a second! The structural adaptations involved in this rapid prey engulfment make this animal’s feeding mechanisms one of the fastest known of all vertebrates.