Anglerfish


The anglerfish are ray-finned fish in the order Lophiiformes. Both the order's common and scientific name comes from the characteristic mode of predation, in which a modified dorsal fin ray acts as a lure for prey. The modified fin ray, with the very tip being the esca and the length of the structure the illicium, is adapted to attract specific prey items across the families of anglerfish by using different luring methods.
Anglerfish occur worldwide. The majority are bottom-dwellers, being demersal fish, while the aberrant deep-sea anglerfish are pelagic, living high in the water column. Some live in the deep sea, while others live in shallower waters, such as the frogfishes and some batfishes.
Anglerfish are notable for their sexual dimorphism, which is sometimes extremely pronounced; the females may be several orders of magnitude larger in mass than males. This dimorphism has enabled a unique reproductive method in the deep-sea anglerfish; sexual parasitism is the attachment of male to the much larger female, sometimes fusing together as an example of natural parabiosis.

Taxonomy

Anglerfish were first grouped in the family of Acanthopterygians with "pediculate pectoral s" by Cuvier in the 1829 edition of Le Règne Animal; being characterized by possessing "a sort of arm supporting their pectorals, formed by an elongated carpal bone". Cuvier placed the genera Lophius, Chironectes/''Antennarius, Malthe, and Batrachus'' within this family. Translations of this work into English and Latin renderred the family name as "Pectorales Pediculati"; which was eventually truncated into Pediculati or Pediculata, these names being used to classify anglerfish through 1926. Though this term saw use in publications as late as the 1970s, Pediculati has fallen out of use.
The group Lophidia was conceived by Samuel Garman in 1899; this group was subdivided into the Lophioids and the Halieutoids based on the orientation of the ilicium's base. By 1905, Lophiiformes came into use, at that time being a suborder of Pediculati.

Classification

The following classification is based on Eschmeyer's Catalog of Fishes :
Alternatively, Lophiiformes may be treated as clade within Acanthuriformes; a 2025 paper defines Lophioidei as equivalent to the prior conception of Lophiiformes and converts the suborders into infraorders. Below are two phylogenetic trees; the left phylogeny elaborates on the relationships of the suborders within Lophiiformes as set out in Pietsch and Grobecker's 1987 Frogfishes of the World: Systematics, Zoogeography, and Behavioral Ecology, while the right phylogeny is based on the 2025 study, where Maile et al combines the analysis of Ultra-Conserved Elements (UCE)s, mitochondrial DNA, and morphological evidence;
Phylogenetic studies have consistently recovered the Lophiiformes as sister-group to the Tetraodontiformes, with both within the larger clade Acanthuriformes as of 2025. The Lophiiformes and Tetraodontiformes are united by several derived morphological features separating them from other Acanthuriformes, including restricted gill openings, along with the absence of multiple skeletal elements, such as spines supporting the anal fin, ribs, nasals, and basisphenoid.

Evolution

The earliest fossils of anglerfish are from the Eocene, excavated from the Monte Bolca formation of Italy, and these already show evidence of diversification into the modern families that make up the order. Given this, and their close relationship to the Tetraodontiformes which are known from Cretaceous fossils, they likely originated during the Cretaceous.
A 2010 mitochondrial genome phylogenetic study suggested the anglerfishes diversified in a short period during the early to mid-Cretaceous, between 130 and 100 million years ago. A 2023 preprint reduces this time to the Late Cretaceous, between 92 and 61 million years ago. Other studies indicate that anglerfish only originated shortly after the Cretaceous-Paleogene extinction event as part of a massive adaptive radiation of percomorphs, although this clashes with the extensive diversity already known from the group by the Eocene. A 2024 study found that all anglerfish suborders most likely diverged from one another during the Late Cretaceous and Paleocene, but the multiple families of deep-sea anglerfishes, as well as their trademark sexual parasitism, originated during the Eocene in a rapid radiation following the Paleocene-Eocene thermal maximum. Adaptations to different ranges of depths may have driven the evolution of anglerfish species and families in prehistory.
Anglerfish appear in the fossil record as follows:

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Anatomy

Anglerfish are defined by gills that open behind the pectoral fins, depressible teeth that can hinge back, joints of the epiotic bone, the form of the pectoral fin radials, and the luring apparatus.
Anglerfish lengths can vary from, with a few larger species than. The largest members are the European monkfish Lophius piscatorius, the deep-sea warty anglerfish Ceratias holboelli, the giant frogfish Antennarius commerson, and the giant triangular batfish Malthopsis gigas.
Many suborders are sexually dimorphic, with the deep-sea anglerfish being the most extreme example; male C. holboelli can reach up to long, while females are commonly around TL, potentially weighing an order of magnitude more than her mate. Male Photocorynus spiniceps were measured to be at maturity, and were at one time claimed to be the smallest vertebrate known. However, due to not being free-living and the females being, they are now often excluded from the records. Sexual dimorphism is not as pronounced in other suborders; the Lophiid monkfish genus Lophiodes are quite similar in size between the genders, and the same is true for Lophius itself.
Anglerfish are generally ambush predators, with shallow-water species such as frogfish often camouflaging as rocks, sponges or seaweed. To blend in with the featureless dark depths they inhabit, deep-sea anglerfish are dark colored, with tints ranging from grey to brown.
In most species, a wide mouth extends all around the anterior circumference of the head, and bands of inwardly inclined teeth line both jaws. The teeth can be depressed so as to offer no impediment to prey gliding towards the stomach, but to still prevent its escape. Anglerfish are able to distend both their jaw and stomach to enormous size, since their bones are thin and flexible, which allows them to swallow prey up to twice as large as their entire bodies.

Esca and illicium

All anglerfish are carnivorous and are thus adapted for the capture of prey. A character shared by all anglerfish suborders is the presence of a "lure" or "bait", unambiguously referred to as the esca. The esca is the tip of a fin ray, modified from the anterior dorsal fin; this fin-ray is often referred to as the "fishing rod" or "fishing line", and is scientifically termed the illicium. The entire illicial apparatus consists of the illicial pterygiophore, followed by a second short dorsal spine, and tipped with the bone of the illicium which ends with the esca proper; this appendage may slot into a groove that accommodates part or all of the illicial apparatus. Both the esca and illicium are used in tandem to lure prey. The illicium's length is highly variable across species, from not being visible at all in some species, to around 4.9 times SL in Gigantactis macronema.
The illicial apparatus is most notable in the deep-sea anglerfish as their esca contain bioluminescent bacteria, making them glow in the dark waters of the deeper pelagic zones. In other species the esca possesses different luring mechanisms, such as emitting odoriferous chemicals that attract olfactory-driven prey, or by resembling prey attractive to small fish such as shrimp or worms. When the prey is close enough, the anglerfish catches it using suction feeding, elongated sharp teeth, or both. While sometimes reported to possess a bioluminescent esca, sea toads lack bioluminescent bacteria and do not actually possess this feature.
In at least the triplewart seadevil, the illicium is moved back and forth by five distinct pairs of muscles: namely the shorter erector and depressor muscles that dictate movement of the illicial bone, along with inclinator, protractor, and retractor muscles that aid motion of the pterygiophore.

Behavior

Predation

The name "anglerfish" derives from the species' characteristic method of predation. Anglerfish typically have at least one long filament sprouting from the middle of their heads, termed the illicium. The illicium is the detached and modified first three spines of the anterior dorsal fin. In most anglerfish species, the longest filament is the first. This first spine protrudes above the fish's eyes and terminates in an irregular growth of flesh, and can move in all directions. Anglerfish can wiggle the esca to make it resemble a prey animal, which lures the anglerfish's prey close enough for the anglerfish to devour them whole. Some deep-sea anglerfish of the bathypelagic zone also emit light from their esca to attract prey.
Because anglerfish are opportunistic foragers, they show a range of preferred prey with fish at the extremes of the size spectrum, whilst showing increased selectivity for certain prey. One study examining the stomach contents of threadfin anglerfish off the Pacific coast of Central America found these fish primarily ate two categories of benthic prey: crustaceans and teleost fish. The most frequent prey were pandalid shrimp. 52% of the stomachs examined were empty, supporting the observations that anglerfish are low energy consumers.

Movement and energy conservation

All anglerfish are weak swimmers, including the pelagic deep-sea anglerfish. Demersal species often "walk" on the bottom upon their pectoral and pelvic fins. The pelvic fins were lost in the deep-sea anglers.
The deep-sea anglers often drift without actively swimming; In situ observation of female Oneirodes and whipnose anglerfish recorded that they often passively float in place or in a current, but they were sometimes observed to attempt to flee from the ROV, beating its pectoral fins in-phase while undulating its tail fin. The lethargic behavior of these ambush predators is suited to the energy-poor environment of the deep sea.
The jaw and stomach of the anglerfish can extend to allow it to consume prey up to twice its size. Because of the limited amount of food available in the anglerfish's environment, this adaptation allows the anglerfish to store food when there is an abundance.
The sea toad Chaunax endeavouri has been observed to retain water in its gills for at least around 26 seconds and up to 4 minutes in some cases. This behavior is thought to be an energy-saving measure as respiration requires energy, thus the fish "holding its breath" may conserve enough energy for such a behavior to be beneficial.

Reproduction

The deep-sea anglerfish employ an unusual mating method: because individuals are locally rare, encounters between two of the same species are also very rare, and finding a mate can be problematic; this has led to the development of sexual parasitism in anglerfish, where the males latch onto their mates using their mouths, which may not be suitable or effective for prey capture. When scientists first started capturing ceratioid anglerfish, they noticed that all of the specimens were female, and on some of these they had what appeared to be parasites attached to them, which turned out to be highly dimorphic male ceratioids. This is one of the few instances of naturally occurring parabiosis. In some species of anglerfish, fusion between male and female when reproducing is possible due to the lack of immune system keys that allow antibodies to mature and create receptors for T-cells.
The spawn of all anglerfish are enveloped by a gelatinous sheath, which has multiple terms referring to it. The spawn of the Lophius anglerfish consists of a thin sheet of transparent gelatinous material wide and may be longer than ; this "egg mass" may contain over a million eggs. The eggs in this sheet are in a single layer, each in its own cavity. The larvae are pelagic and have the pelvic fins elongated into filaments. It is thought that these egg masses effectively disperse their young over great distances and a large area. A female Linophryne arborifera, with a parasitic male, was observed to have numerous eggs embedded in a gelatinous mass protruding from the genital opening; the eggs, 0.6–0.8mm in diameter, are among the largest known for any ceratioid.

Relation to humans

Classical interpretation

In the History of Animals, Aristotle described the "Fishing-Frog" as an example of a marine species well adapted to their environment, those equipped with "ingenious devices" that it uses to capture prey, alongside the Torpedo. He noted that fishing-frogs that have lost their lure appeared to be thinner than those still intact.

As food

Lophiidae, marketed as monkfish or goosefish, are of commercial interest with fisheries found in western Europe, eastern North America, Africa, and East Asia. In Europe and North America, the tail meat of fish of the genus Lophius, known as monkfish or goosefish, is widely used in cooking, and is often compared to lobster tail in taste and texture.
In Africa, the countries of Namibia and the Republic of South Africa record the highest catches. In Asia, especially Japan, monkfish liver, known as ankimo, is considered a delicacy. Anglerfish is especially heavily consumed in South Korea, where it is featured as the main ingredient in dishes such as Agujjim.
Northwest European Lophius species are heavily fished and are listed by the ICES as "outside safe biological limits". In 2010, Greenpeace International added the American angler, the angler, and the black-bellied angler to its seafood red list—a list of fish commonly sold worldwide with a high likelihood of being sourced from unsustainable fisheries. Additionally, anglerfish are known to occasionally rise to the surface during El Niño, leaving large groups of dead anglerfish floating on the surface.

Captivity

Various species of anglerfish are kept in captivity, such as frogfish and batfish, though these are all species that inhabit shallow waters; deep-sea anglerfish have not been kept in captivity due to the challenges of keeping them alive through capture, transport, and a display that can repressurize them.
Antennarius biocellatus is known by the common names brackish-water frogfish or freshwater frogfish; being euryhaline, it can live in freshwater for some time, sometimes claimed to be the sole representative of the anglerfish to live in freshwater. Like many frogfish, it has been displayed in public aquaria, though unlike the other species A. biocellatus are sometimes kept in home aquaria by private aquarists.