Stoplight loosejaw
Encyclopedia
The stoplight loosejaws are small, deep-sea dragonfish
es of the genus Malacosteus, classified either within the subfamily Malacosteinae of the family Stomiidae
, or in the separate family Malacosteidae. They are found worldwide, outside of the Arctic
and Subantarctic
, in the mesopelagic zone below a depth of 500 meters (1,640 ft). This genus once contained three nominal species: M. niger (the type), M. choristodactylus, and M. danae, with the validity of the latter two species being challenged by different authors at various times. In 2007, Kenaley examined over 450 stoplight loosejaw specimens and revised the genus to contain two species, M. niger and the new M. australis.
Malacosteus and the related genera Aristostomias and Pachystomias are the only fishes that produce red bioluminescence
. As most of their prey organisms are not capable of perceiving light at those wavelengths, this allows Malacosteus to hunt with an essentially invisible beam of light. Furthermore, Malacosteus is unique amongst animals in using a chlorophyll
derivative to perceive red light. The name Malacosteus is derived from the Greek
malakos meaning "soft" and osteon meaning "bone". Another common name
for these fishes is "rat-trap fish", from the unusual open structure of their jaw
s.
, while M. australis is found in the southern transition zone between 25° to 45° S, where it is bound by the Antarctic Circumpolar Current
. M. niger appears to be replaced by M. australis south of 30° S, while M. australis does not occur north of that latitude outside of the Indian Ocean
and the Indo-Australian Archipelago
. Both species are usually found below a depth of 500 meters (1,640 ft) in midwater. They are the only known stomiids that do not seem to conduct significant diel vertical migration
s.
Malacosteus has an elongated body with short, blunt snout
s and large eyes that face forward, granting binocular vision
. Unlike other stomiids, it has a single round nostril
on each side in front of the eye. Relative to its size, Malacosteus has one of the widest gapes of any fish, with a lower jaw measuring one-quarter of the fish's length. The lower jaw has no ethmoid membrane (floor) and is attached only by the hinge and a modified tongue bone. There are several large, fang-like teeth in the front of the jaws, followed by many small barbed teeth. There are several groups of pharyngeal teeth
that serve to direct food down the gullet.
The pectoral and pelvic fins are moderately long, containing 3-4 and 6 fin rays respectively. The dorsal
and anal fins are placed far back on the body and contain 18-20 and 19-22 rays respectively. The caudal fin is small, with the lower lobe larger than the upper. There are three bioluminescent photophore
s near the eyes: beneath the eye is a large, teardrop
-shaped suborbital photophore that emits red light. Behind it is an ovoid postorbital photophore that emits green light; this photophore is larger in males than females. These red and green photophores are evocative of traffic light
s, hence the fish's common name. The third is tiny and round, located between the eye and the large red photophore. Several rows and clusters of blue photophores are present on the sides and belly. In addition, there are small photophores and accessory areas of white luminous tissue scattered over the head and body. The skin
is thin and scaleless
; the coloration is black.
As long wavelengths of light (i.e. red) do not reach the deep sea, many deep-sea organisms are red-colored (effectively appearing black) and are insensitive to red wavelengths. The red photophore of Malacosteus thus allows it to illuminate prey without being detected. These fishes exhibit a number of adaptations for feeding on large prey. The "open" structure of its jaws reduces water resistance, allowing them to be snapped shut more quickly, while large recurved teeth and powerful jaw closing muscles assure a secure hold on prey items. The connection between the head and the body is reduced, with unossified
vertebrae, allowing the cranium to be tilted back and the jaws thrust forward for a wider gape. Finally, the gills are exposed to the outside, allowing the fish to continue respiring
while slowly swallowing large prey.
However, contrary to its apparent morphological
specialization, the diet of Malacosteus consists primarily of zooplankton
, chiefly large calanoid copepod
s, with smaller numbers of krill
, shrimp
s, and fish
es. It is yet unclear how Malacosteus captures such small planktonic prey given the open structure of its mouth. The unexpected diet of Malacosteus is theorized to be a result of the small volumes that it searches for food, in which large prey items are rare. The rapid attenuation of red light in sea water gives Malacosteus a shorter visual range than species that use blue light, and it does not migrate vertically into more productive waters like other stomiids. Therefore, its strategy may be one of "snacking" on copepods, which are three orders of magnitude more abundant than fishes at its native depths, in between larger meals.
The other factor believed to be partly responsible for Malacosteus diet is its unique visual system, which uses a derivative of chlorophyll
as a photosensitizer that absorbs long-wave light (around 700 nm) and then indirectly stimulates the fish's two visual pigments, which have maximum absorbances at only 520 and 540 nm. No vertebrate
s are known to synthesize chlorophyll derivatives, and Malacosteus is believed to obtain these derivatives from the copepod
s it consumes. The red photophore of Malacosteus consists of a pigmented sac with a reflective inner lining and an internal mass of gland cells. Inside the gland cells, blue-green light is produced via the same chemical reaction found in other stomiids, which is then absorbed by a protein
that fluoresces
in a broad red band. This light is then reflected out through the photophore apterture, where it passes through a brown filter, yielding a far-red light with a maximum absorbance at 708 nm (almost infra-red). In live fish, the suborbital and postorbital photophores both flash vigorously, the suborbital at a slower rate.
Dragonfish
-Other fish called Dragonfish:*Barbeled dragonfish, small bioluminescent deep-sea stomiiform fish of the family Stomiidae*Arowana, large freshwater osteoglossiform fish of the family Osteoglossidae...
es of the genus Malacosteus, classified either within the subfamily Malacosteinae of the family Stomiidae
Stomiidae
Stomiidae is a family of deep-sea ray-finned fish, including the barbeled dragonfishes, stareaters and loosejaws.Stomiids are generally elongated fish with black or near-black bodies, but they are highly variable in form, and are sometimes grouped into multiple different families as a result. The...
, or in the separate family Malacosteidae. They are found worldwide, outside of the Arctic
Arctic
The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...
and Subantarctic
Subantarctic
The Subantarctic is a region in the southern hemisphere, located immediately north of the Antarctic region. This translates roughly to a latitude of between 46° – 60° south of the Equator. The subantarctic region includes many islands in the southern parts of the Indian Ocean, Atlantic Ocean and...
, in the mesopelagic zone below a depth of 500 meters (1,640 ft). This genus once contained three nominal species: M. niger (the type), M. choristodactylus, and M. danae, with the validity of the latter two species being challenged by different authors at various times. In 2007, Kenaley examined over 450 stoplight loosejaw specimens and revised the genus to contain two species, M. niger and the new M. australis.
Malacosteus and the related genera Aristostomias and Pachystomias are the only fishes that produce red bioluminescence
Bioluminescence
Bioluminescence is the production and emission of light by a living organism. Its name is a hybrid word, originating from the Greek bios for "living" and the Latin lumen "light". Bioluminescence is a naturally occurring form of chemiluminescence where energy is released by a chemical reaction in...
. As most of their prey organisms are not capable of perceiving light at those wavelengths, this allows Malacosteus to hunt with an essentially invisible beam of light. Furthermore, Malacosteus is unique amongst animals in using a chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
derivative to perceive red light. The name Malacosteus is derived from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
malakos meaning "soft" and osteon meaning "bone". Another common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
for these fishes is "rat-trap fish", from the unusual open structure of their jaw
Jaw
The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of...
s.
Distribution and habitat
These fishes have a wide distribution in all oceans: M. niger is found between 66° N and 33° S, except for the Mediterranean SeaMediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
, while M. australis is found in the southern transition zone between 25° to 45° S, where it is bound by the Antarctic Circumpolar Current
Antarctic Circumpolar Current
The Antarctic Circumpolar Current is an ocean current that flows from west to east around Antarctica. An alternative name for the ACC is the West Wind Drift. The ACC is the dominant circulation feature of the Southern Ocean and, at approximately 125 Sverdrups, the largest ocean current...
. M. niger appears to be replaced by M. australis south of 30° S, while M. australis does not occur north of that latitude outside of the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
and the Indo-Australian Archipelago
Indo-Australian Plate
The Indo-Australian Plate is a major tectonic plate that includes the continent of Australia and surrounding ocean, and extends northwest to include the Indian subcontinent and adjacent waters...
. Both species are usually found below a depth of 500 meters (1,640 ft) in midwater. They are the only known stomiids that do not seem to conduct significant diel vertical migration
Diel vertical migration
Diel vertical migration, also known as diurnal vertical migration, is a pattern of movement that some organisms living in the ocean and in lakes undertake each day. Usually organisms move up to the epipelagic zone at night and return to the mesopelagic zone of the oceans or to the hypolimnion zone...
s.
Description
Snout
The snout, or muzzle, is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw.-Terminology:The term "muzzle", used as a noun, can be ambiguous...
s and large eyes that face forward, granting binocular vision
Binocular vision
Binocular vision is vision in which both eyes are used together. The word binocular comes from two Latin roots, bini for double, and oculus for eye. Having two eyes confers at least four advantages over having one. First, it gives a creature a spare eye in case one is damaged. Second, it gives a...
. Unlike other stomiids, it has a single round nostril
Nostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
on each side in front of the eye. Relative to its size, Malacosteus has one of the widest gapes of any fish, with a lower jaw measuring one-quarter of the fish's length. The lower jaw has no ethmoid membrane (floor) and is attached only by the hinge and a modified tongue bone. There are several large, fang-like teeth in the front of the jaws, followed by many small barbed teeth. There are several groups of pharyngeal teeth
Pharyngeal teeth
Pharyngeal teeth are teeth in the pharyngeal arch of the throat of cyprinids, suckers, and a number of other fish species lacking teeth.Popular aquarium fish such as goldfish and loaches have these structures. Members of the Botia genus such as clown loaches are known to make distinctive clicking...
that serve to direct food down the gullet.
The pectoral and pelvic fins are moderately long, containing 3-4 and 6 fin rays respectively. The dorsal
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
and anal fins are placed far back on the body and contain 18-20 and 19-22 rays respectively. The caudal fin is small, with the lower lobe larger than the upper. There are three bioluminescent photophore
Photophore
A photophore is a light-emitting organ which 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...
s near the eyes: beneath the eye is a large, teardrop
Tears
Tears are secretions that clean and lubricate the eyes. Lacrimation or lachrymation is the production or shedding of tears....
-shaped suborbital photophore that emits red light. Behind it is an ovoid postorbital photophore that emits green light; this photophore is larger in males than females. These red and green photophores are evocative of traffic light
Traffic light
Traffic lights, which may also be known as stoplights, traffic lamps, traffic signals, signal lights, robots or semaphore, are signalling devices positioned at road intersections, pedestrian crossings and other locations to control competing flows of traffic...
s, hence the fish's common name. The third is tiny and round, located between the eye and the large red photophore. Several rows and clusters of blue photophores are present on the sides and belly. In addition, there are small photophores and accessory areas of white luminous tissue scattered over the head and body. The skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
is thin and scaleless
Fish scale
Fish scale may refer to:* The rigid plates on the skin of a fish* Fishscale, an album by Ghostface Killah* Fishscale cocaine* Fish Scales, a rapper...
; the coloration is black.
Biology and ecology
Ossification
Ossification is the process of laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation...
vertebrae, allowing the cranium to be tilted back and the jaws thrust forward for a wider gape. Finally, the gills are exposed to the outside, allowing the fish to continue respiring
Respiration (physiology)
'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
while slowly swallowing large prey.
However, contrary to its apparent morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
specialization, the diet of Malacosteus consists primarily of zooplankton
Zooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
, chiefly large calanoid copepod
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
s, with smaller numbers of krill
Krill
Krill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...
, shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
s, and fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
es. It is yet unclear how Malacosteus captures such small planktonic prey given the open structure of its mouth. The unexpected diet of Malacosteus is theorized to be a result of the small volumes that it searches for food, in which large prey items are rare. The rapid attenuation of red light in sea water gives Malacosteus a shorter visual range than species that use blue light, and it does not migrate vertically into more productive waters like other stomiids. Therefore, its strategy may be one of "snacking" on copepods, which are three orders of magnitude more abundant than fishes at its native depths, in between larger meals.
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
as a photosensitizer that absorbs long-wave light (around 700 nm) and then indirectly stimulates the fish's two visual pigments, which have maximum absorbances at only 520 and 540 nm. No vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s are known to synthesize chlorophyll derivatives, and Malacosteus is believed to obtain these derivatives from the copepod
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
s it consumes. The red photophore of Malacosteus consists of a pigmented sac with a reflective inner lining and an internal mass of gland cells. Inside the gland cells, blue-green light is produced via the same chemical reaction found in other stomiids, which is then absorbed by a protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
that fluoresces
Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
in a broad red band. This light is then reflected out through the photophore apterture, where it passes through a brown filter, yielding a far-red light with a maximum absorbance at 708 nm (almost infra-red). In live fish, the suborbital and postorbital photophores both flash vigorously, the suborbital at a slower rate.
Species
- Southern stoplight loosejaw, Malacosteus australis (syn. Malacosteus choristodactylus VaillantSébastien VaillantSébastien Vaillant was a French botanist.Vaillant was born at Vigny, Val d'Oise. He studied medicine at Pontoise, and then moved to Paris to practice as a surgeon, where he studied botany at the Jardin des Plantes under Joseph Pitton de Tournefort.Vaillant was appointed to the staff of the Jardin...
, 1888; Malacosteus danae Regan & Trewavas, 1930; Malacosteus indicus GüntherAlbert C. L. G. GüntherAlbert Karl Ludwig Gotthilf Günther FRS, also Albert Charles Lewis Gotthilf Günther , was a German-born British zoologist, ichthyologist, and herpetologist....
, 1878) This species is mainly distinguished from M. niger by a smaller postorbital photophore in both sexes and lower numbers of lateral photophores. It also differs in having somewhat smaller jaws, a fleshy orbit, and several subtle morphological traits. The maximum known length is 16.6 cm (6.5 in) for a male and 19.2 cm (7.6 in) for a female. Its specific epithet comes from the LatinLatinLatin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
austral, meaning "southern".
- Northern stoplight loosejaw, Malacosteus niger (syn. Malacosteus choristodactylus VaillantSébastien VaillantSébastien Vaillant was a French botanist.Vaillant was born at Vigny, Val d'Oise. He studied medicine at Pontoise, and then moved to Paris to practice as a surgeon, where he studied botany at the Jardin des Plantes under Joseph Pitton de Tournefort.Vaillant was appointed to the staff of the Jardin...
, 1888; Malacosteus danae Regan & Trewavas, 1930; Malacosteus indicus GüntherAlbert C. L. G. GüntherAlbert Karl Ludwig Gotthilf Günther FRS, also Albert Charles Lewis Gotthilf Günther , was a German-born British zoologist, ichthyologist, and herpetologist....
, 1878) The postorbital photophore in this species is larger than in M. australis. It also differs in lateral photophore count, as well as in morphological characters. The maximum known length is 25.6 cm (10.1 in). Its specific epithet niger is Latin for "black".