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Overview

Comprehensive Description

Biology

Warmer-water distribution, within 15° of the Equator. Large adults sometimes kill themselves by swimming out of the water onto beaches; occurrence of such strandings may be linked to certain areas, seasons or months and often in spates. With a unique adaptation of self-amputation (autotomy) of the posterior part of the body past the vent which may involve only the caudal fin (or one to a few small adjacent vertebrae) or as far anterior as just before the abdomen; apparently occurs several times during its lifetime (serial autotomy) but do not damage any vital organs and are usually survived except in strandings. All records over 1.5 m long have bodies shortened by autotomy and may exhibit a healed-over stump or "terminus"; still, many specimens found with fresh (with a ragged appearance very different from a healed termini) incomplete self-amputations of the posterior part of the body, notably not consistent with shark bites; the lost part is never regenerated. Oftentimes sighted vertically suspended head-up in clear oceanic or inshore waters with the rays of the two dorsal fin crests usually extended vertically upward while the pelvic fin rays may be horizontally spread outward and away from the body (Ref. 92949). This is hypothesized to be a feeding stance that visually allows the fish to spot the silhouette of its potential prey against the skylight (Ref. 49905). Feed on euphausiid crustaceans, small fishes and squid (Ref. 6738). Toothless protrusile jaws work to suction krill-laden water into its oro-branchial cavity and retained in the gullet by the long, spiny and bristly gill rakers (Ref. 92949). Occassionally associate in pairs (gender undocumented) but no record of group larger than three or of schooling behavior (Ref. 92949). Spawning occurs between July and December and larvae are encountered near the surface (Ref. 9337). Spawns in the North Pacific Ocean, in an area west of the Marianas Islands; also possibly in South Africa near Durban (Ref. 92949). In Guinness Book of Records as longest bony fish (Ref. 6472). Also caught with encircling nets and marketed fresh (Ref. 9337). Reputed to be unpalatable because the flesh is tasteless or otherwise unappetizing (Ref. 92949). Underwater footage shows them slowly swimming vertically, head up, with a stiff body, only undulating the dorsal fin, and with photophores on their appendages. The mouth can be protruded for capturing prey (RF, pers. comm. 2013). A rare species mainly offshore, sometimes drifting to coastal regions (Ref. 41299). Length based on occurrence record from Taiwan.
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Distribution

Pacific Ocean: Japan, USA (California) and Mexico (Baja California).
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Physical Description

Morphology

Dorsal spines (total): 0; Dorsal soft rays (total): 333 - 371; Analspines: 0; Analsoft rays: 0; Vertebrae: 113 - 122
  • Nakabo, T. 2002 Fishes of Japan with pictorial keys to the species, English edition I. Tokai University Press, Japan, pp v-866. (Ref. 41299)
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Size

Max. size

540 cm SL (male/unsexed; (Ref. ))
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Diagnostic Description

With two red dorsal fin crests up to 1 meter high and ribbon-like silvery body up to 8 meters in length. Distinguished by the dorsal fin rays until end of abdomen fewer than 82; abdominal vertebrae 34 to 37; in complete adult specimens, total vertebrae count, 113 to 122 and total dorsal fin rays, 333 to 371; total gill rakers on first gill arch in large fish, 47 to 60; in adults, anteriormost part of dorsal fin with 2 crests: first dorsal fin crest with 3 to 6 rays united by fin membranes and second dorsal fin crest with a single elongated and ornamented ray and not united by membrane to other dorsal fin rays (Ref. 92949). Other diagnostic characters: pelvic fin with a single elongated ray and with more than 3 membranous appendages; caudal fin small, reduced (Ref. 41299). Cristophore (new term) present and supports the first dorsal fin crest; pelvic fin with a single permanent, extremely elongate and ornamented ray; 11-14 pectoral-fin rays, with a horizontally-oriented base, allowing the fin to be vertically-oriented when adpressed against the body; all large fish lacking a caudal fin, but in the young, principal rays number 3-4 (usually 4), may be extremely elongate, and the tip rarely with ornament; lacking procurrent rays; highly elongate body, with no anal fin; total dorsal fin rays in complete specimens (significantly less in individuals of approx. max. TL of 1.5 m), 3 33 to 449 and total vertebrae 113 to 163; approx. max. length of largest specimens, 8 m (all autotomized); stomach characterized with an elongate postabdominal caecum extending to end of body; muscle masses compartmentalized by a complex system of connected intermuscular septa; with up to three dorsal horizontal septa and three ventral horizontal septa in addition to the horizontal, vertical, and transverse septa common to most teleosts; as a result of autotomy, the posterior part of the adult body (including most large juveniles) terminating in a healed-over stump or terminus (new term); still, many specimens found with fresh (with a ragged appearance very different from a healed termini) incomplete self-amputations of the posterior part of the body, notably not consistent with shark bites. Toothless jaws or with only some tiny vestigial teeth (Ref. 92949).
  • Nakabo, T. 2002 Fishes of Japan with pictorial keys to the species, English edition I. Tokai University Press, Japan, pp v-866. (Ref. 41299)
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Ecology

Habitat

Environment

bathypelagic; marine
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Depth range based on 1 specimen in 1 taxon.

Environmental ranges
  Depth range (m): 35 - 35
 
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Trophic Strategy

Warmer-water distribution, within 15° of the Equator. (Ref. 92949). Large adults sometimes kill themselves by swimming out of the water onto beaches; occurrence of such strandings may be linked to certain areas, seasons or months and often in spates (Ref. 92949). Feed on euphausiid crustaceans, small fishes and squid (Ref. 6738); Euphausiidae being their main diet but possibly feed only when highly concentrated in areas of upwelling. With few predators and parasites; adaptative significance of autotomy still unknown. Occassionally associate in pairs (gender undocumented) but no record of group larger than three or of schooling behavior. Spawns in the North Pacific Ocean, in an area west of the Marianas Islands; also possibly in South Africa near Durban (Ref. 92949).
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Life History and Behavior

Life Cycle

Are broadcast spawners with no parental care for the young (Ref. 92949).
  • Breder, C.M. and D.E. Rosen 1966 Modes of reproduction in fishes. T.F.H. Publications, Neptune City, New Jersey. 941 p. (Ref. 205)
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Regalecus russelii

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 1
Species With Barcodes: 1
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Conservation

Threats

Not Evaluated
  • IUCN 2006 2006 IUCN red list of threatened species. www.iucnredlist.org. Downloaded July 2006.
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Relevance to Humans and Ecosystems

Benefits

Importance

fisheries: of no interest
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