Anglerfish are a group of ray-finned fish that constitute the order Lophiiformes. They derive their name from the modified dorsal spine, which functions like a fishing rod to lure prey, much as a human angler would. This spine ends in a club-like structure, which acts as a bait for the prey. Around 350 species of anglerfish are found across oceans worldwide, of which roughly 200 are deep-sea forms. Many of these deep-sea species also exhibit sexual parasitism, in which much smaller males attach to and fuse with the body of a larger female, forming a permanent reproductive pair.
These fish typically range from 1 to 7 in (2 to 18 cm). However, some of the largest species, such as Krøyer’s deep-sea angler fish (Ceratias holboelli), have a maximum standard length (SL) of 30 in (77 cm) in adult females. Others, such as European anglers (Lophius piscatorius), have an average size of 16 to 24 in (40 to 60 cm).[1][2]
Males of one of the smallest anglerfish species, Photocorynus spiniceps, measure between 0.24 and 0.29 in (6.2 to 7.3 mm).[3]
Members of the suborder Ceratioidei exhibit extreme sexual dimorphism, with the females being considerably larger than the males. For example, although females of Krøyer’s deep-sea angler fish measure 30 in (77 cm), their males can reach only up to 6.3 in (16 cm).
They have a distinctly large head relative to their body size, equipped with a mouth that opens wide enough to swallow prey often larger than themselves. The jaws are flexible and protrude outwards when feeding. Their teeth are long, needle-like, and point inwards to prevent prey from escaping.
Their first dorsal spine is a long, thin, flexible rod called the illicium. The tip of this spine is modified into a fleshy bulb called the esca. Together, the esca and the illicum function as a fishing rod or fishing line, acting as a lure for their prey. Females of most deep-sea anglerfish possess bioluminescent esca containing symbiotic bacteria that produce light.
Some anglerfish, such as batfishes (family Ogcocephalidae), possess a glandular esca, which produces odoriferous chemicals that attract olfactory-driven prey.
In some species, such as Gigantactis macronema, the length of the illicium is about 5 times the standard length of their bodies, whereas in others, it may be barely visible.
Unlike most fish, where the pectoral fins lie behind the gill opening, anglerfish are distinguished by their gills positioned behind the pectoral fins.
According to Eschmeyer’s Catalog of Fishes (2025), all anglerfish species are classified into 5 suborders and 15 families.
The oldest fossils of anglerfish (representative of the species Sharfia mirabilis) have been excavated from the Monte Bolca formation of Italy, dating back to the Eocene Epoch (around 50 million years ago).[4]
Anglerfish have a worldwide distribution, ranging from tropical to polar waters. While most deep-sea species live between approximate depths of 200 and 2000 m (656 and 6560 ft), relatively shallow-water anglerfish, such as frogfishes, live at depths of up to 100 m (330 ft).
They are mostly bottom-dwellers (demersal), lying partially buried in sediments, though deep-sea anglerfish are pelagic, living high in the water column.[5]
These fish are strictly carnivorous, feeding opportunistically on small fish species (primarily teleosts), crustaceans (including shrimp, crabs, and amphipods), and squid.
Anglerfish are ambush predators that typically remain camouflaged as rocks, sponges, or seaweed, lurking in anticipation of prey. Deep-sea anglerfish are specifically dark colored (in shades of grey to black) to blend in with the darkness of the depths.
To attract their prey, anglerfish wave the illicium, making the esca appear like a small animal. Once they have caught the prey’s attention, they wait for it to approach them. As the prey comes within range, these fish quickly open their jaws, protruding both jaws outwards. This rapid expansion of the buccal cavity produces a powerful suction flow, pulling the prey straight in.
Compared to other fish, anglerfish are relatively slow swimmers. Some species, such as red-lipped batfish (Ogcocephalus darwini), have been observed moving on their pectoral, pelvic, and anal fins, almost in a walking-like gait.[6]
In controlled environments, a few deep-sea anglerfish, such as whipnose anglers (family Gigantactinidae), have been observed fleeing from remotely operated vehicles (ROVs) by beating their pectoral fins while undulating their tail fins.[7]
The longevity of anglerfish varies with species. For example, the European angler survives a maximum of 24 years in the wild, whereas the American anglerfish (Lophius americanus) has the highest recorded lifespan of 30 years.[8][9]
All anglerfish reproduce sexually, though mating and fertilization vary among the species, depending on the habitat they occupy. Owing to the dark environment they stay in, deep-sea anglerfish find it extremely hard to find mates, and thus, they use the permanent male-to-female fusion (sexual parasitism) mechanism to mate. Once a male finds a female, he bites into her skin. Over time, their tissues fuse, the male’s organs gradually degenerate (except his testes), and he becomes a permanent, living sperm provider attached to the female. In fact, a single female may carry multiple males fused to her body. When the female is ready to spawn, she releases her eggs into the water, and the attached male releases his sperm simultaneously, resulting in external fertilization.
Their eggs are typically embedded in a gelatinous sheet or ribbon, or in a raft-like mass that keeps the eggs together. The egg mass of Lophius may be longer than 10 m (33 ft), containing over a million eggs.
The eggs hatch into tiny, transparent larvae that have their pelvic fins elongated into filaments. These larvae initially derive nutrition from the yolk sac, later switching to feeding as they grow. Within 2 to 4 months, the larval filaments disintegrate, and the larvae stop drifting, instead settling onto the reef or seafloor as transparent juveniles. Eventually, the juveniles become adults and attain sexual maturity in 2 to 6 years.
Unlike deep-sea anglerfish, shallow-water species have no need for sexual parasitism because males and females can easily find each other. They meet briefly, release their gametes for external fertilization, and the life cycle continues.
Although anglerfish are predators themselves, they are vulnerable to other aquatic animals in the wild. Deep-sea anglerfish have very few confirmed predators, with occasional predation reported from large demersal fishes, including some sharks. In contrast, shallow-water anglerfish face greater predation pressure. They may be eaten by large predatory fish, such as cod and sharks, as well as by marine mammals like seals, particularly during the juvenile stage.
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