Anglerfish

This article is about the larger group of anglerfish including shallow water forms. For deep-sea anglerfish with a luminescent lure, see deep-sea anglerfish.

The anglerfish are ray-finned fish in the order Lophiiformes (/ˌlɒfiɪˈfɔːrmiːz/).^[2] 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 (akin to a human angler, and likened to a crest or "lophos"). 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 Temporal range: Eocene-present PreꞒ Ꞓ O S D C P T J K Pg N Probable Cretaceous origin
Type species of 4 lophiiform suborders; Ogcocephalus vespertilio, Ceratias holboelli, Lophius piscatorius, and Chaunax pictus. The type species of the genus Antennarius needs clarification
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Clade:	Percomorpha
Order:	Lophiiformes Sedgwick et. al., 1905[1]
Type species
Lophius piscatorius Linnaeus, 1758
Synonyms
Pediculati Müller, 1839 (pro parte)

Anglerfish occur worldwide. The majority are bottom-dwellers, being demersal fish, while the aberrant deep-sea anglerfish are pelagic, (mostly) living high in the water column. Some live in the deep sea (such as the deep-sea anglerfish and sea toads), while others live in shallower waters, such as the frogfishes and the batfish.

Anglerfish are notable for their sexual dimorphism, which is sometimes extremely pronounced; the males may be several orders of magnitude smaller in mass than females. 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

"Pediculati" plate in Le Règne Animal. Toadfish (Batrachoididae) such as Batrachoides surinamensis (middle) are no longer considered close to anglerfish

Anglerfish were first grouped in the family of Acanthopterygians with "pediculate pectoral [fin]s" (pectorales pédiculėes) by Cuvier in the 1829 edition of Le Règne Animal;^[3] being characterized by possessing "a sort of arm supporting their pectorals, formed by an elongated carpal bone". Cuvier placed the genera Lophius (incl. Lophius piscatorius), Chironectes/Antennarius (incl. various subspecies of Lophius histrio), Malthe (incl. Lophius vespertilio), and Batrachus within this family.^[3] Translations of this work into English and Latin renderred the family name as "Pectorales Pediculati";^[4][5] which was eventually truncated into Pediculati or Pediculata (pediculate fish),^{[6][7][8][9][10][11]} these names being used to classify anglerfish through 1926.^{[12][13][14][15][16][17]} Though this term saw use in publications as late as the 1970s,^[11] Pediculati has fallen out of use.^[18]

The group Lophidia was conceived by Samuel Garman in 1899;^[19] this group was subdivided into the Lophioids (incl. Lophius, Lophiomus, Melanocetus, Dolopichthys, Chaunax, and Chaunacops) and the Halieutoids (incl. Oncocephalus, Halieutaea, Halieutella, Halieutichthys, Halieutopsis, Halicmetus, Dibranchus, Dibranchichthys, and Malthopsis) based on the orientation of the ilicium's base.^[19] By 1905, Lophiiformes came into use, at that time being a suborder of Pediculati.^[1]

Classification

Anglerfishes are classified by the 5th edition of Fishes of the World into 5 suborders and 18 families.^[20][21] The following taxa have been arranged to show their evolutionary relationships.^[22][23]

• Suborder Lophioidei Regan, 1912
  • Family Lophiidae Rafinesque, 1810 (Monkfishes and goosefishes)
• Suborder Antennarioidei Regan, 1912
  • Family Antennariidae Jarocki 1822 (Frogfishes)
  • Family Tetrabrachiidae Regan, 1912 (Tetrabrachid frogfishes)
  • Family Lophichthyidae Boeseman, 1964 (Lophichthyid frogfishes)
  • Family Brachionichthyidae Gill, 1863 (Handfishes or warty anglerfishes)
• Suborder Chaunacoidei Pietsch & Grobecker, 1987
  • Family Chaunacidae Gill, 1863 (Sea toad)
• Suborder Ogcocephaloidei Pietsch, 1984
  • Family Ogcocephalidae Gill, 1893 (Batfishes)
• Suborder Ceratioidei Regan, 1912
  • Family Caulophrynidae Goode & Bean, 1896 (Fanfins)
  • Family Neoceratiidae Regan, 1926 (Spiny seadevils)
  • Family Melanocetidae Gill, 1878 (Black seadevils)
  • Family Himantolophidae Gill, 1861 (Footballfishes)
  • Family Diceratiidae Regan & Trewavas, 1932 (Double anglers)
  • Family Oneirodidae Gill, 1878 (Dreamers)
  • Family Thaumatichthyidae Smith & Radcliffe, 1912 (Wolftrap anglers)
  • Family Centrophrynidae Bertelsen, 1951 (Prickly seadevils)
  • Family Ceratiidae Gill, 1861 (Warty seadevils)
  • Family Gigantactinidae Boulenger, 1904 (Whipnose anglers)
  • Family Linophrynidae Regan, 1925 (Leftvents)

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 is shown below.^[24]

Lophiiformes	Lophioidei Antennarioidei Chaunacoidei Ogcocephaloidei Ceratioidei

Phylogenetic studies have recovered Lophiiformes as the sister group of Tetraodontiformes, within the larger clade Acanthuriformes and so classified as clades within that taxon.^[25]

Evolution

The earliest fossils of anglerfish are from the Eocene Monte Bolca formation of Italy, and these already show diversification into the modern families that make up the order.^[26] Given this, and their close relationship to the Tetraodontiformes which are known from Cretaceous fossils, they likely originated during the Cretaceous.^[27][28]

A 2010 mitochondrial genome phylogenetic study suggested the anglerfishes diversified in a short period of the early to mid-Cretaceous, between 130 and 100 million years ago.^[24] A more recent preprint reduces this time to the Late Cretaceous, between 92 and 61 million years ago.^[28] 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.^[28][29] 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 (Ceratioidei), as well as their trademark sexual parasitism, originated during the Eocene in a rapid radiation following the Paleocene-Eocene thermal maximum.^[30]

Anglerfish appear in the fossil record as follows:^{[31][32][33][34]}

Anatomy

The sargassumfish (Histrio histrio, 20 cm (7.9 in) TL) is a frogfish well-adapted to live among sargassum

Anglerfish are defined by gills that open behind the pectoral fins, as opposed to other fish whose pectorals lay behind the gill opening, and the luring apparatus (see subsection).^[35]

Anglerfish lengths can vary from 2–18 cm (1–7 in), with a few types getting as large as 100 cm (39 in).^[36] The largest members are the European monkfish (Lophius piscatorius; 200 centimetres (6.6 ft) SL, 57.7 kilograms (127 lb)) and the deep-sea Ceratias holboelli (120 centimetres (3.9 ft) TL).^[37][38]

Many suborders are sexually dimorphic, with the deep-sea anglerfish being the most extreme example; male C. holboelli can reach up to 16 centimetres (6.3 in) long (SL), while females are commonly around 77 centimetres (2.53 ft) TL.^[38][22] Male Photocorynus spiniceps were measured to be 6.2–7.3 mm (0.24–0.29 in) at maturity, and were at one time claimed to be the smallest vertebrate known. However, due to not being free-living (being parasitic males) and the females being 50.5 mm (1.99 in), they are now often excluded from the records.^{[39][40][41][42]} Sexual dimorphism is not as pronounced in other suborders; the Lophiid monkfish genus Lophiodes are quite similar in size between the genders (Mean for Males 113–133 millimetres (4.4–5.2 in) SL; Females 131–171 millimetres (5.2–6.7 in) SL),^[43] and the same is true for Lophius proper (Males 68.50–129.50 centimetres (2.247–4.249 ft); Females 93.50–166.60 centimetres (3.068–5.466 ft)).^[44]

Shallow-water anglerfish species such as frogfish are ambush predators, often camouflaging as rocks, sponges or seaweed.^[45] To blend in with the featureless dark depths they inhabit, deep-sea anglerfish are dark colored, with tints ranging from grey to brown.^{[36][better source needed]}

In most species, a wide mouth extends all around the anterior (front) circumference of the head, and bands of inwardly inclined teeth line both jaws. The teeth can be depressed (swept back) so as to offer no impediment to prey gliding towards the stomach, but to still prevent its escape.^{[46][better source needed]} 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.^{[36][better source needed]}

Esca and illicium

Striated frogfish (Antennarius striatus), displaying the worm-like esca at the top left

All anglerfish are carnivorous and are thus adapted for the capture of prey.^[36] 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 "-line" and is scientifically termed the illicium. The illicial apparatus consists of the illicial pterygiophore (the "base" of the structure), followed by a second short dorsal spine, and tipped with the illicial bone and esca proper, all of which may slot into a groove that accommodates part or all of the illicial apparatus.^{[47]: 33–40} Both the esca and illicium are used in tandem to lure prey.^{[48][49][50][51][52][35]} The illicium's length is highly variable across species, from not being visible at all in some species, to around 4.9 times SL (over 4 times the length of the rest of the body) in Gigantactis macronema (body length 354 mm (13.9 in)).^{[47]: 469 [53]}

This illicial apparatus is most notable in the deep-sea anglerfish (Ceratioidei) as their esca contain bioluminescent bacteria, making them glow in the dark waters of the deeper pelagic zones.^{[54][55][56][52]} In other species the esca possesses different luring mechanisms, such as emitting odoriferous chemicals that attract olfactory-driven prey (batfish, Ogcocephaloidei; possibly sea toads, Chaunacioidei), or by resembling prey attractive to small fish such as shrimp or worms (frogfish, Antennarioidei). When the prey is close enough, the anglerfish catches it using suction feeding, elongated sharp teeth, or both.^{[35][57][47]: 263} While sometimes reported to possess a bioluminescent esca, sea toads lack bioluminescent bacteria and do not actually possess this feature.^[57][58]

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.^[59]

Behavior

Predation

Skeleton of the anglerfish Lophius piscatorius: The first spine of the dorsal fin of the anglerfish acts as a fishing rod with a lure.

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 (the esca), 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.^[60] Some deep-sea anglerfish of the bathypelagic zone also emit light from their esca to attract prey.^[61]

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.^{[62] [63]}

Movement and energy conservation

Red-lipped batfish "standing" on the benthos

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 latter fin pair having been lost in deep-sea anglers.^{[52][better source needed]}

In 2005, near Monterey, California at 1,474 metres depth, an ROV filmed a female ceratioid anglerfish of the genus Oneirodes for 24 minutes. When approached, the fish retreated rapidly, but in 74% of the video footage, it drifted passively, oriented at any angle. When advancing, it swam intermittently at a speed of 0.24 body lengths per second, beating its pectoral fins in-phase. The lethargic behavior of this ambush predator is suited to the energy-poor environment of the deep sea.^[64]

In situ observation of three different female whipnose anglerfish showed unusual inverted (upside-down) swimming behavior; the fish were observed floating inverted completely motionless with the illicium hanging down stiffly in a slight arch in front of the fish, hanging over small burrows in the substrate. It was suggested this is an effort to entice prey and an example of low-energy opportunistic foraging and predation. When the ROV approached the fish, they exhibited burst swimming, remaining inverted.^[65]

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.^{[citation needed]}

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.^[66]

Reproduction

Linophrynidae: Haplophryne mollis female anglerfish with males attached

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.^[67] 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.^[22] 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.^[68]

Further information: Ceratioidei § Sexual parasitism

The spawn of the anglerfish of the genus Lophius consists of a thin sheet of transparent gelatinous material 25 cm (10 in) wide and may be longer than 10 m (33 ft); this "egg mass" may contain over a million eggs.^[69][44] 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.^[44][46] A 77 millimetres (3.0 in) female Linophryne arborifera, with a 15 millimetres (0.59 in) parasitic male, was observed to have numerous eggs embedded in a gelatinous mass (an "egg raft" or "veil") protruding from the genital opening; the eggs, 0.6–0.8mm in diameter, are among the largest known for any ceratioid.^[70][22]

Relation to humans

One family, the Lophiidae, is 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 (North America), 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.^[44] In Asia, especially Japan, monkfish liver, known as ankimo, is considered a delicacy.^[71] 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".^[72] Additionally, anglerfish are known to occasionally rise to the surface during El Niño, leaving large groups of dead anglerfish floating on the surface.^[72]

In 2010, Greenpeace International added the American angler (Lophius americanus), the angler (Lophius piscatorius), and the black-bellied angler (Lophius budegassa) to its seafood red list—a list of fish commonly sold worldwide with a high likelihood of being sourced from unsustainable fisheries.^[73][47]