The angler fish is a predator named for the way it hunts: a fin ray on its head works like a fishing rod, with a lure at the tip that draws prey close enough to swallow. Anglerfish (order Lophiiformes) live in oceans worldwide, from tropical seas to polar waters, and from shallow reefs down into the deep sea, where some species carry a lure that glows.
Deep-sea anglerfish use a glowing lure to attract prey in the dark. The light comes from bioluminescent bacteria that live inside the lure. When a smaller fish swims in to investigate, the anglerfish opens its huge mouth and pulls the prey in by suction.
Anglerfish also have one of the strangest love lives in the animal kingdom. In many deep-sea species the males are tiny and attach themselves to a much larger female, and in some species the two bodies fuse for life.
Angler fish key facts
- Scientific order: Lophiiformes, which includes monkfishes, frogfishes, batfishes, sea toads and the deep-sea anglerfishes (suborder Ceratioidei).
- Where they live: marine waters worldwide, from shallow seas to the deep ocean. Most deep-sea anglerfish adults live between about 200 and 3,000 meters (660 to 9,840 feet) down.
- Size: most species are 2 to 18 cm (1 to 7 inches) long. The largest is the European monkfish, recorded at about 2 meters (6.6 feet) and 57.7 kg (127 lb).
- The lure: the “rod” is called the illicium and the bait at its tip is the esca. In most deep-sea species the esca glows thanks to bacteria.
- Diet: carnivores. Their jaws and stomachs stretch so far that they can swallow prey up to twice their own size.
- Mating: in some deep-sea species the tiny male bites onto the female and fuses with her, a habit known as sexual parasitism.
- As food: monkfish (also sold as goosefish) are caught commercially, and their tail meat is often compared to lobster.
Main source for these figures: Anglerfish on Wikipedia and Ceratioidei (deep-sea anglerfishes) on Wikipedia.
Fascinating Biology of Anglerfish
Anglerfish have unusual features that help them survive where food is scarce. Their bodies, mouths and fishing rod appendages are all built for ambush rather than chase.
Distinctive Features
Anglerfish have big heads and wide mouths lined with inward-pointing teeth. The teeth can fold back, so prey slides in easily but cannot get out again. Their most striking feature is the fishing rod that grows from their heads. This rod, called an illicium, is a modified spine of the dorsal fin, and it ends in a lure known as the esca.
The illicium is not fixed in place. Muscles let the fish extend it, pull it back, or wave the lure in front of its mouth. In some species the rod can be folded away into a groove on the head.
Deep-sea anglerfish are dark grey to brown, which hides them in the black water around them. Shallow-water relatives such as frogfish are camouflaged instead to look like rocks, sponges or seaweed.
Lophiiformes: The Order of Anglerfish
Anglerfish belong to the order Lophiiformes. This group includes the bottom-dwelling monkfishes, frogfishes, batfishes and sea toads, as well as the free-floating deep-sea anglerfishes.
Bottom-dwelling species use their fins to rest on or walk across the seabed. The deep-sea anglerfish have lost their pelvic fins and spend their lives drifting in open water. All anglerfish are weak swimmers.
Deep Sea Habitat and Distribution
Anglerfish occur in marine waters around the world, from tropical seas to polar regions. Some live in shallow water, while the best known species live far below the surface in the deep sea.
Ocean’s Depths: Home of the Anglerfish
Adults of most deep-sea anglerfish species live between about 200 and 3,000 meters (660 to 9,840 feet) deep. One genus, Thaumatichthys, has been found as deep as 6,000 meters (20,000 feet). Sunlight does not reach these depths, the water is cold and the pressure is intense.
Food is scarce down there, so anglerfish save energy. They often float in place or drift with the current, waiting for prey to come to the lure rather than hunting it down.
Geographical Spread Worldwide
Anglerfish live in the Atlantic, Pacific, Indian and Southern Oceans. Monkfish fisheries exist in western Europe, eastern North America, Africa and East Asia, which shows how widely the bottom-dwelling species are spread.
Some species have more limited ranges. The brackish-water frogfish can even live in fresh water for a while, which is unusual for an anglerfish.
Reproduction and Life Cycle
Male and female anglerfish can look very different. In the deep sea, where meeting a partner is rare, this difference has led to one of the most unusual mating systems known.
Mating Rituals
In many deep-sea species, tiny males attach to big females. The male bites the female and holds on. In some species his body fuses with hers and they share a blood supply, so he becomes a permanent source of sperm.
The size gap can be enormous. Males of the warty seadevil reach about 16 cm (6.3 inches), while females are commonly around 77 cm (2.5 feet). Mature males of one species, Photocorynus spiniceps, measure only 6 to 7 mm.
Fusion is possible because some anglerfish have lost parts of the immune system that would normally reject another animal’s tissue. Not every species fuses: in some, the male only attaches for a while.
Development from Eggs to Adults
Anglerfish eggs are wrapped in a jelly-like sheath. Monkfish release their eggs in a transparent sheet about 25 cm (10 inches) wide that can be more than 10 meters (33 feet) long and may hold over a million eggs.
The eggs hatch into larvae that drift in the water. Deep-sea anglerfish larvae live much higher than the adults, usually in the top 30 meters (98 feet), and move deeper as they grow.
Adaptations for Survival
Anglerfish survive in the deep, dark sea by making light, hiding well and wasting as little energy as possible.
Bioluminescence
In most deep-sea anglerfish the lure contains bioluminescent bacteria that make it glow. Depending on the species, the light can range from pink or purple to white, yellow, green or blue, although blue-green light travels farthest in water and is the color most deep-sea animals see best.
Not every anglerfish glows. Batfish appear to attract prey with chemicals that smell like food, and frogfish have lures that look like small shrimp or worms.
Camouflage Techniques
Anglerfish are ambush predators, so hiding matters. Deep-sea species are dark grey to brown and disappear against the black water. Shallow-water frogfish look like rocks, sponges or algae and wait motionless until prey comes close.
Diet: What Anglerfish Eat
All anglerfish are carnivorous. They are opportunistic feeders that take whatever the lure brings within reach.
Feeding Habits
When prey gets close, the anglerfish opens its mouth suddenly and sucks the animal in. Thin, flexible bones let both the jaw and the stomach stretch, so an anglerfish can swallow prey up to twice its own size and store food when it is plentiful.
Common prey include:
- Small fish
- Shrimp and other crustaceans
- Squid
- Worms, snails and other bottom animals (for species living near the seabed)
Role in the Food Chain
Anglerfish are important predators in ocean ecosystems. One study of threadfin anglerfish found that more than half of the stomachs examined were empty, a sign of how rarely these low-energy hunters eat and how important each catch is.
Anglerfish Physical Characteristics
Anglerfish bodies are shaped by how they live. Frogfish are short and use limb-like fins to crawl, batfish and sea toads are flattened or round bottom-dwellers, and deep-sea anglerfish are soft-bodied drifters.
Size Comparisons
Most anglerfish are small, between 2 and 18 cm (1 and 7 inches) long. A few species grow beyond 1 meter (39 inches). The record holders are the European monkfish, at about 2 meters (6.6 feet) and 57.7 kg (127 lb), and the deep-sea warty seadevil, at about 1.2 meters (3.9 feet).
In deep-sea species the females are far bigger than the males and can weigh many times more.
Color Variations and Skin
Deep-sea anglerfish are usually dark grey, brown or black. Frogfish come in a wider range of colors and textures that match their surroundings on reefs and seabeds.
Most anglerfish have big mouths with sharp teeth angled inward, which helps them hold onto prey in the dark.
Interaction with Humans
Anglerfish matter to people as food, as aquarium animals and as the unlikely stars of countless deep-sea pictures.
Anglerfish in Fisheries
Monkfish, also called goosefish in North America, are fished commercially. Their tail meat is widely used in European and North American cooking. In Japan, monkfish liver, called ankimo, is a delicacy, and anglerfish is a main ingredient in the Korean dish agujjim.
Some stocks are under pressure. Northwest European monkfish species have been listed by ICES as outside safe biological limits, and in 2010 Greenpeace added three Lophius species to its seafood red list.
Anglerfish in Aquariums
Shallow-water anglerfish such as frogfish and batfish are kept in public aquariums. Deep-sea anglerfish have never been kept alive in captivity, because they rarely survive being brought up from the high pressure of the deep.
Conservation Status and Threats
Most deep-sea anglerfish live far beyond the reach of fishing nets, so the main pressure falls on the bottom-dwelling monkfishes that people eat.
Population Concerns
The European monkfish (Lophius piscatorius) is heavily fished, and its biology and status are monitored closely. Overfishing, bycatch and changes in ocean conditions are the main risks for fished species.
Scientific Research and Studies
When scientists first caught deep-sea anglerfish, every specimen seemed to be female, and some carried what looked like parasites. Those “parasites” turned out to be the males.
Contributions to Marine Biology
Research into how males fuse with females has shown that some anglerfish have lost key parts of the immune system, something that would be fatal to most vertebrates. Studies of the glowing lure have also helped scientists understand how fish and bacteria live together.
Understanding Anglerfish Behavior
Remotely operated vehicles have filmed deep-sea anglerfish alive in their habitat. The footage shows them mostly floating still, and occasionally beating their fins to flee from the camera.
Evolutionary History of Anglerfish
The earliest anglerfish fossils come from the Eocene Monte Bolca formation in Italy, and they already show several modern families. A 2010 genetic study suggested anglerfish diversified between 130 and 100 million years ago, in the Cretaceous, while later studies point to later dates.
A 2024 study found that the deep-sea anglerfish families, and their habit of sexual parasitism, appeared in the Eocene in a rapid burst of evolution after a period of global warming.
One well known deep-sea species is Melanocetus johnsonii, the humpback anglerfish, a good example of how these fish adapted to life in the dark.
Frequently asked questions
Where do angler fish live?
Anglerfish live in oceans worldwide, from tropical to polar waters. Monkfish, frogfish and batfish live on or near the seabed, often in shallow water. Deep-sea anglerfish mostly live between about 200 and 3,000 meters (660 to 9,840 feet) below the surface.
Why do angler fish glow?
The glow comes from bioluminescent bacteria living inside the lure, or esca, at the tip of the fish’s fishing rod. The light attracts curious prey in the dark, and the anglerfish swallows whatever comes close.
How big do angler fish get?
Most species are only 2 to 18 cm (1 to 7 inches) long. The biggest is the European monkfish, which can reach about 2 meters (6.6 feet) and 57.7 kg (127 lb). In deep-sea species, females are far larger than males.
Are angler fish dangerous to humans?
No. Deep-sea anglerfish live far below the depths people reach, and most species are small. The ones people encounter most are monkfish, which end up on dinner plates.
Do male angler fish really fuse with females?
In some deep-sea species, yes. The tiny male bites onto the female and their tissues and blood supply join, so he stays attached for life and provides sperm. In other species the male only clings on for a time.