Telescopefish are small, deep-sea

aulopiform Aulopiformes is a diverse order of marine ray-finned fish consisting of some 15 extant and several prehistoric families with about 45 genera and over 230 species. The common names grinners, lizardfishes and allies, or aulopiforms are sometimes ...

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

comprising the small

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Giganturidae. The two known species are within the

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

''Gigantura''. Though rarely captured, they are found in cold, deep tropical to subtropical waters worldwide. The common name of these fish is related to their bizarre, tubular

eye An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...

s. The genus name ''Gigantura'' refers to the

Gigantes In Greek mythology, Greek and Roman mythology, the Giants, also called Gigantes (Ancient Greek, Greek: Γίγαντες, ''wiktionary:gigantes, Gígantes'', Γίγας, ''wiktionary:gigas, Gígas''), were a race of great strength and aggression, ...

, a race of

giants A giant is a being of human appearance, sometimes of prodigious size and strength, common in folklore. Giant(s) or The Giant(s) may also refer to: Mythology and religion *Giants (Greek mythology) * Jötunn, a Germanic term often translated as 'g ...

Greek mythology Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, and a genre of ancient Greek folklore, today absorbed alongside Roman mythology into the broader designation of classical mythology. These stories conc ...

—coupled with the suffix ''oura'', meaning 'tail', thus ''Gigantura'' refers to the greatly elongated, ribbon-like lower half of the tailfin that may comprise over half of the total body length.

Species

The currently recognized species in this genus are: * '' Gigantura chuni'' A. B. Brauer, 1901 (gigantura) * Gigantura indica A. B. Brauer, 1901 (telescopefish)

Description

The Giganturidae are slender, slightly tapered fish with large heads dominated by large, forward-pointing, telescoping eyes with large

lenses A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...

. Their heads end in short, pointed snouts. The highly extensile mouth is lined with sharp, slightly recurved and depressible teeth and it extends well past the eyes. The body lacks scales, but is covered in easily abraded, silvery

guanine Guanine () (symbol G or Gua) is one of the four main nucleotide bases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine ( uracil in RNA). In DNA, guanine is paired with cytosine. The guanine nucleoside ...

, which imparts a greenish to purplish

iridescence Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear gradually to change colour as the angle of view or the angle of illumination changes. Iridescence is caused by wave interference of light in microstru ...

in life. The

gas bladder The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled organ in bony fish that functions to modulate buoyancy, and thus allowing the fish to stay at desired water depth without having to maintain lift via swimming, ...

is absent and the

stomach The stomach is a muscular, hollow organ in the upper gastrointestinal tract of Human, humans and many other animals, including several invertebrates. The Ancient Greek name for the stomach is ''gaster'' which is used as ''gastric'' in medical t ...

is highly distensible. The transparent

fin A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. F ...

s are spineless; the deeply forked and hypocercal

caudal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

is most striking, with the lower lobe extended to a length exceeding that of the body. The

pectoral fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish aquatic locomotion, swim. Apart from the tail or caudal fin, fish fins have no direct connection with the vertebral column ...

s are large (about 30–42

rays Ray or RAY may refer to: Fish * Ray (fish), any cartilaginous fish of the superorder Batoidea * Ray (fish fin anatomy), the bony or horny spine on ray-finned fish Science and mathematics * Half-line (geometry) or ray, half of a line split at an ...

), situated above the

gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow r ...

opening, and inserted horizontally. The

anal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported o ...

(about 8–14 rays) and single

dorsal fin A dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...

(about 16–19 rays) are both situated far back of the head. The

pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral (belly) surface of fish, and are the lower of the only two sets of paired fins (the other being the laterally positioned pectoral fins). The pelvic fins are homologous to the hi ...

s and

adipose fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only b ...

are absent. Also absent are the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...

orbitosphenoid The lesser wings of the sphenoid or orbito-sphenoids are two thin triangular plates, which arise from the upper and anterior parts of the body, and, projecting lateralward, end in sharp points ig. 1 In some animals, they remain as separate bones ...

, parietal, symplectic, posttemporal, and

supratemporal The supratemporal bone is a paired Skull, cranial bone present in many Tetrapod, tetrapods and Tetrapodomorpha, tetrapodomorph fish. It is part of the temporal region (the portion of the skull roof behind the eyes), usually lying medial (inwards) re ...

bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...

s, the

gill raker Gill rakers in fish are bony or cartilaginous processes that project from the branchial arch (gill arch) and are involved with suspension feeding tiny prey. They are not to be confused with the gill filaments that compose the fleshy part of th ...

s, and the branchiostegal rays. The loss of these structures is attributed to

neoteny Neoteny (), also called juvenilization,Montagu, A. (1989). Growing Young. Bergin & Garvey: CT. is the delaying or slowing of the Physiology, physiological, or Somatic (biology), somatic, development of an organism, typically an animal. Neoteny i ...

; that is, the retention of

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

l characteristics. '' Gigantura indica'' is the larger of the two species at about standard length (a measurement excluding the caudal fin). However, '' Gigantura chuni'' (at about standard length) is slightly more robust in build. Both species within the genus have been recently observed in Australian waters and have a very similar species distribution.

Life history

Telescopefish are presumed to be solitary, active

predator Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...

s, frequenting the

mesopelagic The mesopelagic zone (Greek language, Greek μέσον, middle), also known as the middle pelagic or twilight zone, is the part of the pelagic zone that lies between the photic epipelagic and the aphotic bathypelagic zones. It is defined by light ...

to bathypelagic zones of the water column, from . By using their tubular, large-lensed eyes—which are adapted for optimal binocular light collection, at the expense of lateral vision—telescopefish are likely able to spy their prey's weak

bioluminescence Bioluminescence is the emission of light during a chemiluminescence reaction by living organisms. Bioluminescence occurs in multifarious organisms ranging from marine vertebrates and invertebrates, as well as in some Fungus, fungi, microorgani ...

from a distance, as well as (by looking skyward) resolve the outlined silhouettes of prey against the gloom above. Their eyes may also help telescopefish to better judge distance of prey; these visual adaptations are typical of deep-sea fish (

barrel-eye Barreleyes, also known as spook fish (a name also applied to several species of chimaera), are small deep-sea argentiniform fish comprising the family Opisthoproctidae found in tropical-to-temperate waters of the Atlantic, Pacific, and Indian O ...

tube-eye ''Stylephorus chordatus'', the tube-eye or thread-tail, is a deep-sea ray-finned fish, the only species in the genus ''Stylephorus'' and family Stylephoridae. It is found in deep subtropical and tropical oceans around the world, living at depths ...

). Common prey include

bristlemouth The Gonostomatidae are a family of mesopelagic marine fish, commonly named bristlemouths, lightfishes, or anglemouths. It is a relatively small family, containing only eight known genera and 32 species. However, bristlemouths make up for their l ...

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

, and

barbeled dragonfish Stomiidae is a family (biology), family of deep-sea ray-finned fish, including the barbeled dragonfishes, that live in all oceans in a wide range of depths. They are quite small, usually around 15 cm, up to 26 cm, and they exhibit a st ...

. Owing to the telescopefishes' highly extensile jaws and distensible stomachs, they are able to swallow prey larger than themselves; this is also a common adaptation to life in the lean depths ( sabertooth fish,

black seadevil Black seadevils are small, deep-sea lophiiform fish of the family Melanocetidae. The six known species are all within the genus ''Melanocetus''. They are found in tropical to temperate waters of the Atlantic, Indian, and in the Pacific Oceans ...

). Telescopefish participate in the

diel vertical migration Diel vertical migration (DVM), also known as diurnal vertical migration, is a pattern of movement used by some organisms, such as copepods, living in the ocean and in lakes. The adjective "diel" ( IPA: , ) comes from , and refers to a 24-hour ...

in which

mesopelagic fish Pelagic fish live in the pelagic zone of ocean or lake waters—being neither close to the bottom nor near the shore—in contrast with demersal fish that live on or near the bottom, and reef fish that are associated with coral reefs. ...

migrate to the surface at night to feed before returning to the depths to shelter during the day. Much less is known of their

reproductive The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are al ...

habits. They are presumed to be nonguarding pelagic

spawn Spawn or spawning may refer to: * Spawning, the eggs and sperm of aquatic animals Arts, entertainment and media * Spawn (character), a fictional character in the comic series of the same name and in the associated franchise ** ''Spawn: Armageddon' ...

ers, releasing

eggs An egg is an organic vessel in which an embryo begins to develop. Egg, EGG or eggs may also refer to: Biology * Egg cell, the female reproductive cell (gamete) in oogamous organisms Food * Eggs as food Places * Egg, Austria * Egg, Switzerland ...

and

sperm Sperm (: sperm or sperms) is the male reproductive Cell (biology), cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm ...

indiscriminately into the water. The fertilized eggs are buoyant and become incorporated into the

zooplankton Zooplankton are the heterotrophic component of the planktonic community (the " zoo-" prefix comes from ), having to consume other organisms to thrive. Plankton are aquatic organisms that are unable to swim effectively against currents. Consequent ...

, wherein they and the larvae remain—likely at much shallower depths than the adults—until

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth transformation or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and different ...

into juvenile or adult form.

Species

Description

Life history

See also

References

Further reading