Sloane's viperfish, ''Chauliodus sloani'', is a predatory mesopelagic dragonfish found in waters across the world. The species was first described by German scientists Marcus Elieser Bloch and Johann Gottlob Schneider in their 1801 book ''Systema ichthyologiae: iconibus CX illustratum'', volume 1.Bloch, M. E., & Schneider, J. G. (1801). ''Systema ichthyologiae: iconibus CX illustratum'' (Vol. 1). Auctor. Female ''C. sloani'' reach maturity between 133 and 191 mm, while males likely reach maturity at slightly smaller body lengths. It has two rows of

photophores A photophore is a glandular organ that appears as luminous spots on various marine animals, including fish and cephalopods. The organ can be simple, or as complex as the human eye; equipped with lenses, shutters, color filters and reflectors, h ...

along its ventral side.Whitehead, P. J. P., Bauchot, M. L., Hureau, J. C., Nielsen, J., & Tortonese, E. (1984). Fishes of the north-eastern Atlantic and the Mediterranean, volume 1. United Nations Educational Scientific and Cultural Organization. It is believed that ''C. sloani'' can adjust the intensity of bioluminescence of the ventral photophores to camouflage itself from predators that might see its shadow from below.

Taxonomy

''C. sloani'' is part of the genus Chauliodus, which includes all viperfishes.

Viperfish A viperfish is any species of marine fish in the genus ''Chauliodus''. Viperfishes are mostly found in the mesopelagic zone and are characterized by long, needle-like teeth and hinged lower jaws. A typical viperfish grows to lengths of . Viper ...

es are deep-sea fishes with photophores (light-producing organs), long teeth, and hinged jaws. There are nine other species in the genus, including ''C. danae'' and ''C. pammelas'', both of which appear alongside ''C. sloani'' in primary literature.van Utrecht, W. V. U. C. (1987). Growth and seasonal variations in distribution of ''Chaulidous sloani'' and ''C. danae'' (Pisces) from the mid North Atlantic. ''Bijdragen tot de Dierkunde'', ''57''(2), 164-182.Butler, M., Bollens, S. M., Burkhalter, B., Madin, L. P., & Horgan, E. (2001). Mesopelagic fishes of the Arabian Sea: distribution, abundance and diet of Chauliodus pammelas, Chauliodus sloani, Stomias affinis, and Stomias nebulosus. ''Deep Sea Research Part II: Topical Studies in Oceanography'', ''48''(6-7), 1369-1383. ''C. sloani'' is distinguished from other ''Chauliodus'' species by its circumglobal range.

Distribution

''C. sloani'' is found in tropical and temperate waters. It is widespread in the

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth#Surface, Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Afr ...

and the western

Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ...

, as well as the Indian and

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

Oceans. In the Atlantic, its latitudinal range is from 35°N - 55°N, with highest abundance around 45°N. In the

Arabian Sea The Arabian Sea ( ar, اَلْبَحرْ ٱلْعَرَبِيُّ, Al-Bahr al-ˁArabī) is a region of the northern Indian Ocean bounded on the north by Pakistan, Iran and the Gulf of Oman, on the west by the Gulf of Aden, Guardafui Channel ...

, its range is primarily south of 10°N. In the central Mediterranean Sea, ''C. sloani'' is eaten as a primary part of the diet of the

Atlantic bluefin tuna The Atlantic bluefin tuna (''Thunnus thynnus'') is a species of tuna in the family Scombridae. It is variously known as the northern bluefin tuna (mainly when including Pacific bluefin as a subspecies), giant bluefin tuna or individuals excee ...

. Analysis of several cetaceans' stomach contents found remnants of ''C. sloani'', including the

pygmy sperm whale The pygmy sperm whale (''Kogia breviceps'') is one of two extant species in the family Kogiidae in the sperm whale superfamily. They are not often sighted at sea, and most of what is known about them comes from the examination of stranded spec ...

and

Gervais's beaked whale Gervais's beaked whale (''Mesoplodon europaeus''), sometimes known as the Antillean beaked whale, Gulf Stream beaked whale, or European beaked whale (from which its scientific name is derived) is the most frequently stranding type of mesoplodont ...

. Both were found beached on the Canary Islands.

Anatomy

Jaw anatomy

The primary feature of interest in ''C. sloani'' is its enormous teeth. When the jaw is closed, the teeth fit together to form a cage in which prey can likely be trapped.Greven, H., Walker, Y., & Zanger, K. (2009). On the structure of teeth in the viperfish Chauliodus sloani Bloch & Schneider, 1801 (Stomiidae). ''Bulletin of Fish Biology Volume'', ''11''(1/2), 87-98. Its jaw can be unhinged, allowing it to open its mouth up to 90° to catch prey up to 63% its own body size. Its teeth, however, are fixed in place, attached firmly to the jawbone rather than being depressible like in some other fish species. The immobility of its huge teeth requires it to open its jaw so wide. The size, shape, location, and number of teeth are consistent across individuals of ''C. sloani'', and each fang is highly specialized. ''C. sloani'' likely lures prey to its mouth with its photophore, or by arching its long dorsal ray to dangle in front of its mouth. The foremost premaxillary tooth, which is relatively straight and has sharp ridges, may then be used to wound larger prey. The curved second premaxillary tooth is thought to be used like a dagger, retaining larger prey.⁵ All teeth come together into a cage to retain smaller prey. A study in 2009 showed that the teeth of ''C. sloani'' have dentin tubules while another study, a decade later, showed the teeth of '' Aristostomias scintillans'', another member of the family Stomiidae, lack dentin tubules. The reason behind difference in presence of dentin tubules in two species of the same family has yet to be addressed. The jaw musculature of ''C. sloani'' contains a third adductor facialis muscle ventral to the skull. Recent research suggests that it improves the mechanical advantage of the system by anteriorly displacing the intersegmental aponeurosis during adduction, which increases bite force and angular velocity.

General anatomy

''C. sloani'' has a forked caudal fin, an adipose fin, and a dorsal fin located immediately behind its head. Almost all of its fins contain soft rays. ''C. sloani'' has a low lipid content (~2.4%). The body is enveloped in a thick, transparent, gelatinous casing. Like many stomiiformes, its scales and caudal skeleton are poorly ossified and it lacks a gas-filled swim bladder.

Diet

''C. sloani'' is a major consumer of myctophids (

lanternfish Lanternfishes (or myctophids, from the Greek μυκτήρ ''myktḗr'', "nose" and ''ophis'', "serpent") are small mesopelagic fish of the large family Myctophidae. One of two families in the order Myctophiformes, the Myctophidae are represented ...

es). An average ''C. sloani'' individual probably consumes at least one lanternfish every twelve days and there is no evidence to suggest that they increase their intake of food the bigger they are. Consequently, the stomachs of smaller individuals have been found containing proportionally larger prey than the prey found in the stomachs of larger individuals. However, they are not picky in their diet — they also eat other fishes, eggs, and algae. This is another thing that distinguishes them from the ''C. danae'', which feeds mainly on

crustaceans Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gr ...

, however there has been evidence that shows smaller variations had crustaceans included in the stomach during stomach content analysis. ''C. sloani'' typically feed on large prey, and in some cases was documented to consume prey up to 50% of its own bodyweight, and the size of their prey allows them to feed rarely and opportunistically while maximizing energetic efficiency. This is consistent with the observation that only individuals under 120 mm in length were found with crustaceans in their stomach contents. The fish is considered a specialist predator given the small list of prey that were observed in the stomach content analysis. In a study to determine the effect of seasonal changes on feeding behavior, no significant difference was determined for ''C. sloani'', and all of the prey items observed were fishes. Earlier research found that of the 28 fish species preyed on, 18 were myctophids. There was no observation of a diurnal feeding pattern, meaning their feeding was not affected by time of day.

Bioluminescence

The photophores on the ventral and lateral sides of the viperfish allow it to display bioluminescence. In a recent study, it was determined that the hormones adrenaline and noradrenaline both contribute to bioluminescence in the viperfish, with adrenaline levels being higher in the photophores. The study also observed that when the tail of the viperfish was squeezed, the viperfish emitted light for about 5–10 seconds.

References

{{Taxonbar, from=Q849341 Chauliodus Fish of the Red Sea Taxa named by Marcus Elieser Bloch Taxa named by Johann Gottlob Theaenus Schneider Fish described in 1801