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Telescopefish
Telescopefish
Telescopefish
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Telescopefish
Gigantura chuni
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Aulopiformes
Family: Giganturidae
Genus: Gigantura
A. B. Brauer, 1901

Telescopefish are small, deep-sea aulopiform fish comprising the small family Giganturidae. Telescopefish can be found at the depths of 2000 meters under water. The two known species are within the genus 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 eyes. The genus name Gigantura refers to the Gigantes, a race of giants in Greek mythology—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

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The currently recognized species in this genus are:[1]

  • Gigantura chuni A. B. Brauer, 1901 (gigantura)
  • Gigantura indica A. B. Brauer, 1901 (telescopefish)

Description

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The Giganturidae are slender, slightly tapered fish with large heads dominated by large, forward-pointing, telescoping eyes with large lenses. 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, which imparts a greenish to purplish iridescence in life. The gas bladder is absent and the stomach is highly distensible.

The transparent fins are spineless; the deeply forked and hypocercal caudal fin is most striking, with the lower lobe extended to a length exceeding that of the body. The pectoral fins are large (about 30–42 rays), situated above the gill opening, and inserted horizontally. The anal fin (about 8–14 rays) and single dorsal fin (about 16–19 rays) are both situated far back of the head. The pelvic fins and adipose fin are absent.

Also absent are the premaxilla, orbitosphenoid, parietal, symplectic, posttemporal, and supratemporal bones, the gill rakers, and the branchiostegal rays. The loss of these structures is attributed to neoteny; that is, the retention of larval characteristics.

Gigantura indica is the larger of the two species at about 20.3 centimetres (8 in) standard length (a measurement excluding the caudal fin). However, Gigantura chuni (at about 15.6 centimetres (6.1 in) 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.[2]

Life history

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Telescopefish are presumed to be solitary, active predators, frequenting the mesopelagic to bathypelagic zones of the water column, from 500 to 3,000 metres (1,640 to 9,840 ft). 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 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, tube-eye). Common prey include bristlemouths, lanternfish, and barbeled dragonfish. 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).

Telescopefish participate in the diel vertical migration in which mesopelagic fish migrate to the surface at night to feed before returning to the depths to shelter during the day.[3]

Much less is known of their reproductive habits. They are presumed to be nonguarding pelagic spawners, releasing eggs and sperm indiscriminately into the water. The fertilized eggs are buoyant and become incorporated into the zooplankton, wherein they and the larvae remain—likely at much shallower depths than the adults—until metamorphosis into juvenile or adult form.

See also

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References

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Further reading

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Telescopefish

View on Grokipedia
from Grokipedia
The telescopefish (Gigantura spp.) comprises two rare species of small, deep-sea fishes in the family Giganturidae and order Aulopiformes: Gigantura chuni and Gigantura indica. These synchronous hermaphrodites inhabit the mesopelagic and bathypelagic zones of tropical and subtropical oceans worldwide, occurring circumglobally at depths of approximately 500–2,000 meters. Characterized by their highly derived, elongated bodies up to 20 cm in total length, scaleless silvery skin, forward-directed tubular eyes with large lenses for detecting bioluminescent prey in the dark, and a long ribbon-like tail comprising nearly half their length, telescopefishes exhibit a bizarre morphology adapted to the deep ocean. A notable feature is their specialized apparatus, which allows them to ingest and fold prey larger than their own body size within the stomach. Observations suggest they may form pair bonds, potentially as a strategy.

Taxonomy

Genus and Etymology

The telescopefishes belong to the family Giganturidae, a small group within the order Aulopiformes and class , comprising ray-finned fishes adapted to deep-sea environments. The genus Gigantura is the sole genus in this family, encompassing two recognized that exhibit highly derived morphological features distinguishing them from other aulopiforms, such as their extreme body elongation and specialized sensory structures. Within the broader phylogeny of Aulopiformes, Giganturidae is positioned in the suborder Giganturoidei. The genus name Gigantura derives from the Latin gigas or giganteum (referring to giants in ) combined with the Greek oura (tail), alluding to the disproportionately long, ribbon-like tail that constitutes nearly half the total body length in these fishes. The common name "telescopefish" stems from their prominent, tubular eyes that protrude forward like , an for enhanced vision in the dim . The genus was first established by German zoologist August Brauer in 1901, based on specimens collected during the Valdivia expedition (1898–1899), the inaugural German deep-sea research voyage organized by marine biologist Carl Chun. This expedition yielded numerous novel deep-sea discoveries, with Gigantura chuni honoring Chun directly and G. indica named for its type locality in the near the Chagos Islands; subsequent descriptions were refined in , confirming their distinct species status.

Known Species

The genus Gigantura comprises two recognized species of telescopefish, both deep-sea predators adapted to mesopelagic and bathypelagic environments. Gigantura chuni Brauer, 1901, is the of the , originally described from specimens collected during the German Valdivia expedition in the and named in honor of marine biologist Carl Chun. This species occurs in the tropical Atlantic, Indian, and Pacific Oceans, typically at depths of 500–2000 m. It reaches a maximum standard length of 15.6 cm, with an elongated body and a pronounced ribbon-like tail comprising nearly half its total length; diagnostic features include 30–33 pectoral fin rays and 8–10 anal fin rays. Gigantura indica Brauer, 1901, was described from specimens captured in the during the same expedition, with a primarily circumglobal distribution in tropical to subtropical waters, often overlapping with G. chuni in the but extending more broadly. Slightly larger than its congener, it attains up to 20.3 cm in standard length (or 26 cm total length), featuring a more slender profile and differences such as 36–42 pectoral fin rays and 11–14 anal fin rays. Taxonomic synonymy includes historical treatments of G. indica as a subspecies (Gigantura chuni indica Brauer, 1901), reflecting early uncertainties in distinguishing the two based on limited material, though both are now accepted as valid with no ongoing major controversies. The rarity of specimens—fewer than 300 documented occurrence records combined globally as of recent assessments—has occasionally led to misidentifications, particularly in distinguishing juveniles or damaged individuals. Both species share adaptations such as tubular eyes for detecting , though specifics vary slightly between them.

Physical Description

Body Morphology

Telescopefish, belonging to the Gigantura, exhibit a highly specialized, elongated body form adapted to the deep-sea environment. Their bodies are slender and ribbon-like, often described as eel-shaped, with a scaleless that provides a silvery sheen for in the dim light of mesopelagic and bathypelagic zones. This translucent, silvery lacks scales and features a loose outer layer over a thick mesenchymal jelly underlayer, enhancing buoyancy and reducing visibility to predators. Adult specimens typically reach a maximum standard length of about 20 cm for G. indica and 15.6 cm for G. chuni, though total lengths including the tail can extend to 26 cm. The tail is particularly distinctive, comprising over half the total body length due to its whip-like structure formed by extremely elongated rays in the lower caudal lobe, which can reach up to twice the standard length. The caudal fin is deeply forked and hypocercal, with 16 principal rays (10 in the upper lobe and 6 in the lower), facilitating precise vertical movements through the . Pectoral fins are reduced in prominence, positioned high above the openings with 30–42 rays, but lack pelvic and adipose fins entirely, contributing to the streamlined profile. The dorsal fin is single and spineless with 16–19 soft rays, while the anal fin has 8–14 soft rays, both positioned posteriorly to support subtle maneuvering. The head is relatively large and terminal, featuring a wide mouth equipped with small, sharp teeth suited for grasping prey, though lacking barbels or photophores typical of some deep-sea fishes. The jaws are highly distensible, supported by a unique palatine as the primary tooth-bearing bone in the upper jaw, enabling the ingestion of prey larger than the fish's body. Sexual dimorphism is minimal, as telescopefish are synchronous hermaphrodites, with no pronounced differences in size or form between sexes reported; however, G. indica specimens show slight variations in overall length that may relate to reproductive maturity.

Sensory Adaptations

The telescopefish (Gigantura spp.) possesses highly specialized tubular eyes that protrude prominently from the head and are directed forward to provide . These eyes function analogously to telescopes, with a large spherical lens that maximizes light collection in the dim (500–2,000 m depth), enabling the fish to detect faint silhouettes of prey against light from the surface. Unlike the upward-directed tubular eyes common in many other mesopelagic fishes, such as those in the families Opisthoproctidae and Sternoptychidae, the anterior orientation in telescopefish supports predation by enhancing and resolution in the horizontal plane. The within these tubular eyes exhibits adaptations for extreme low-light conditions, featuring a thick main retina with an area centralis of high cell density (up to 55 × 10³ cells/mm²) that confers spatial resolving power of 4–9 cycles per degree. Optimized for wavelengths (λ_max ≈ 480 nm), the photoreceptors—primarily with multiple rod opsins—provide exceptional sensitivity to bioluminescent signals, allowing detection of prey at distances of several body lengths in near-total darkness. An accessory lines the tubular walls, offering low-resolution to monitor lateral threats, though it lacks a distinct central area. Beyond vision, other sensory systems in telescopefish are subordinated to the dominant visual apparatus, as indicated by brain area volumes in G. vorax. Olfactory organs are reduced relative to visual structures, with a smaller suggesting limited reliance on chemical cues in the sparse mesopelagic environment. The system, comprising sensory canals along the body, remains functional for detecting water vibrations and pressure changes from nearby prey movements, complementing the eyes in prey localization.

Habitat and Distribution

Geographic Range

Telescopefish of the genus Gigantura exhibit a circumglobal distribution across all major oceans, primarily inhabiting tropical to subtropical waters. The two recognized species, G. chuni and G. indica, are recorded in the Atlantic, Indian, and Pacific Oceans, with occurrences concentrated in open oceanic regions between approximately 40°N and 40°S, avoiding polar and high-latitude areas. In the Atlantic Ocean, telescopefish have been documented off the northeastern coast of , including the Archipelago and , marking the first records in Brazilian waters from expeditions in 2015 and 2017. In the , sightings include the , where the first observation of G. indica was captured by remotely operated vehicle (ROV) in 2001 at a depth of 1,214 meters during a (MBARI) expedition. Additional records from the further support their widespread but patchy presence in subtropical gyres, with modeling indicating higher suitability in the South Atlantic and s for G. chuni. Their distribution shows latitudinal limits aligned with warmer water masses, with G. chuni modeled between 32°N and 42°S and G. indica between 35°N and 36°S, reflecting niche across basins. Gaps in occurrence are noted in regions of intense , such as eastern boundary currents, where environmental factors like nutrient levels may limit suitability.

Environmental Preferences

Telescopefish, Gigantura, primarily occupy the mesopelagic to bathypelagic zones of the , at depths ranging from 500 to 2,000 meters, with occasional records extending to 2,100 meters. They are most frequently encountered between 1,000 and 2,000 meters, where ambient light levels are negligible, facilitating their reliance on detection for hunting. These thrive in conditions, with preferred temperatures spanning 2.4 to 9.4°C and a mean of 4.1°C, as recorded across their global occurrences. The high hydrostatic pressures at these depths, exceeding 100 atmospheres, are a defining feature of their , alongside consistently low oxygen concentrations typical of the mesopelagic realm, often within oxygen minimum zones (OMZs) between 500 and 1,000 meters. Telescopefish favor stable thermal environments, such as persistent thermoclines in tropical and subtropical waters, which maintain the narrow temperature range essential for their . Like many mesopelagic species, telescopefish undertake diel vertical migrations, ascending toward the surface at night to feed before descending to deeper waters during the day. They appear to avoid regions with strong currents, preferring calmer, stratified waters that align with their vertically oriented swimming posture and energy-conserving lifestyle. Their distribution is notably influenced by OMZs, where expanded low-oxygen layers in tropical oceans concentrate suitable by limiting overlap with shallower, more dynamic layers.

Biology and Ecology

Life Cycle

Telescopefish exhibit a reproductive strategy characterized by synchronous hermaphroditism, where individuals possess both ovarian and testicular tissues capable of simultaneous function, facilitating in the deep-sea environment. They are oviparous, releasing buoyant eggs that undergo , with spawning likely occurring in deep waters and potentially year-round in tropical regions. Like many deep-sea species, they have low reproductive output. The eggs hatch into pelagic larvae that inhabit the epipelagic zone, primarily between 30-170 m depth, with an extended developmental period featuring neotenic characteristics. The transformation to the adult form is drastic; the first described larva in 1954 was mistaken for a new species, Rosaura rotunda. Following , the juveniles descend to mesopelagic or bathypelagic depths, adapting to the adult habitat. Little is known about growth to or lifespan, though population resilience suggests a maximum age greater than 3 years. High larval mortality results primarily from predation in the surface waters, while adults benefit from extended supported by their low metabolic rates in the , stable deep-sea environment.

Feeding and Behavior

Telescopefish (genus Gigantura) are carnivorous predators with a diet consisting primarily of small mesopelagic fishes, crustaceans such as decapod , and cephalopods including , as revealed by stomach content analyses of specimens from the and North Pacific. These prey items reflect opportunistic feeding on vertically migrating micronekton and in food-limited bathypelagic environments, where telescopefish occupy high trophic levels (approximately 3.4–3.7) supported largely by epipelagic carbon sources. As predators, telescopefish employ a vertical hovering strategy in the , orienting their bodies head-upward to maximize detection of prey silhouettes or bioluminescent signals from above using their specialized tubular eyes. This posture facilitates rapid strikes enabled by their enormous gape and highly extensile jaws, allowing them to engulf prey items potentially larger than their own body size despite their reduced musculature. The absence of bioluminescent organs in telescopefish underscores their reliance on acute vision for prey location rather than active emission for attraction or . Adult telescopefish exhibit solitary behavior with minimal observed social interactions, though rare in situ observations suggest possible pair-bonding during ; they are non-migratory, remaining in stable bathypelagic depths without significant diel vertical excursions. In deep-sea ecosystems, they serve as minor predators, facilitating trophic transfer by consuming abundant micronekton and contributing to the overall energy flow in mesopelagic and bathypelagic food webs.

References

  1. https://www.biotaxa.org/Zootaxa/article/view/zootaxa.5053.1.1/68938
  2. https://fwcs.oregonstate.edu/150-species/telescopefish
  3. https://www.fishbase.se/summary/Gigantura-chuni
  4. https://repository.library.noaa.gov/view/noaa/8561/noaa_8561_DS1.pdf
  5. https://fishesofaustralia.net.au/home/species/2788
  6. https://onlinelibrary.wiley.com/doi/10.1111/zoj.12469
  7. https://www.fishbase.se/summary/FamilySummary.php?family=Giganturidae
  8. https://repository.si.edu/server/api/core/bitstreams/4f3fdd5e-e865-47d8-a24e-75b281207cf7/content
  9. https://www.fishbase.se/summary/Gigantura-chuni.html
  10. https://www.fishbase.se/summary/Gigantura-indica.html
  11. https://www.marinespecies.org/aphia.php?p=taxdetails&id=158858
  12. https://www.fishbase.se/summary/Gigantura-indica
  13. https://www.researchgate.net/publication/303159918_Records_of_telescope_fish_Gigantura_indica_Aulopiformes_Giganturidae_around_Japan
  14. https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2022.1044565/full
  15. https://bioone.org/journals/copeia/volume-2008/issue-4/CG-07-082/Macropinna-microstoma-and-the-Paradox-of-Its-Tubular-Eyes/10.1643/CG-07-082.short
  16. https://pubmed.ncbi.nlm.nih.gov/9406644/
  17. https://www.science.org/doi/10.1126/science.aav4632
  18. https://karger.com/bbe/article-abstract/57/3/117/46448/Sensory-Brain-Areas-in-Mesopelagic-Fishes
  19. https://doi.org/10.1111/jfb.15155
  20. https://lumcon.edu/wp-content/uploads/2017/08/Bockus-and-Seibel-2016.pdf
  21. https://www.researchgate.net/publication/329202453_The_First_In_Situ_Encounter_of_Gigantura_chuni_Giganturidae_Giganturoidei_Aulopiformes_Cyclosquamata_Teleostei_with_a_Preliminary_Investigation_of_Pair-Bonding
  22. https://www.fishbase.se/references/FBRefSummary.php?ID=7449
  23. https://life-in-water.fandom.com/wiki/Telescopefish
  24. https://dash.harvard.edu/bitstreams/816463f7-c760-4a47-97b9-eb393ce56464/download
  25. https://academic.oup.com/icesjms/article-pdf/76/3/662/31238381/fsy074.pdf
  26. https://www.annualreviews.org/doi/full/10.1146/annurev-marine-010816-060543
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