Oarfish
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Agrostichthys
Regalecus
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Oarfish are large, greatly elongated, pelagic lampridiform fish comprising the small family Regalecidae. Found in all temperate to tropical oceans yet rarely seen, the oarfish family contains four species in two genera. One of these, the king of herrings (Regalecus glesne), is listed in the Guinness Book of World Records as the longest bony fish alive, at up to 11 metres in length.
The common name oarfish is presumably in reference to either their highly compressed and elongated bodies or the shape and use of their pelvic fins. The family name Regalecidae is derived from the Latin regalis, meaning "royal". The occasional beachings of oarfish after storms, and their habit of lingering at the surface when sick or dying, have given oarfish a place in maritime folklore as the probable source of many sea serpent tales.
Although the larger species are considered gamefish and are (to a minor extent) fished for commercially, oarfish are rarely caught alive; their flesh is not well regarded due to its gelatinous consistency.
Physical description
The tapering, ribbony silver bodies of oarfish—together with an impressive, pinkish to cardinal red dorsal fin—help explain the perception of majesty taken from rare encounters. The dorsal fin originates from above the (relatively small) eyes and runs the entire length of the fish. Of the ca. 400 dorsal fin rays, the first 10–12 are elongated to varying degrees, forming a trailing crest embellished with reddish spots and flaps of skin at the ray tips. The pelvic fins are similarly elongated and adorned, reduced to 1–5 rays each. The pectoral fins are greatly reduced and situated low on the body. The anal fin is completely absent and the caudal fin may be reduced or absent as well, with the body tapering to a fine point. All fins lack true spines.
Like other members of their order, oarfish have small yet highly protrusible oblique mouths with no visible teeth. The body is scaleless and the skin covered with easily abraded, silvery guanine. In the streamer fish (Agrostichthys parkeri), the skin is clad with hard tubercles. All species lack gas bladders and the number of gill rakers is variable.
Oarfish coloration is also variable; the flanks are commonly covered with irregular bluish to blackish streaks, black dots, and squiggles. These markings quickly fade following death. The king of herrings is by far the largest member of the family at a published total length of 11 metres (with unconfirmed reports of 15 metres or more) and 272 kilograms in weight. The streamer fish is known to reach 3 metres total length whilst the largest recorded specimen of Regalecus russelii measured just 5.5 centimetres standard length.
Life history
Rare encounters with divers and accidental catches by trawls have supplied what little is known of oarfish behaviour and ecology. Apparently solitary animals, oarfish may frequent significant depths from 20–1,000 metres. It was not until 2001 that an oarfish was filmed alive and in situ: the 1.5 metre fish was spotted by a group of US Navy personnel during the inspection of a buoy in the Bahamas [1]. The oarfish was observed to propel itself via an amiiform mode of swimming; that is, rhythmically undulating the dorsal fin whilst keeping the body itself straight. Perhaps indicating a feeding posture, oarfish have been observed swimming in a vertical orientation, with their long axes perpendicular to the ocean surface. In this posture the downstreaming light would silhouette the oarfishes' prey, making them easier to spot.
Oarfish feed primarily on zooplankton, selectively straining tiny euphausiids, shrimp, and other crustaceans from the water. Small fish, jellyfish, and squid are also taken. Large open-ocean carnivores are all likely predators of oarfish, and include the Oceanic Whitetip Shark.
The oceanodromous Regalecus glesne is recorded as spawning off Mexico from July to December; all species are presumed to be non-guarders and release buoyant eggs which are incorporated into the zooplankton. Larvae and juveniles have been observed drifting just below the surface, where they too feed primarily on plankton. In contrast, adult oarfish are rarely seen at the surface when not sick or injured.
See also
References
- Froese, Rainer; Pauly, Daniel (eds.). "Family Regalecidae". FishBase. February 2005 version.
- "Woman angler lands legendary sea monster". Russell Jenkins. February 2005 version. The Times Online; Feburary 21, 2003.
- Fishes: An Introduction to ichthyology. Peter B. Moyle and Joseph J. Cech, Jr; p. 338. Printed in 2004. Prentice-Hall, Inc; Upper Saddle River, NJ. ISBN 0131008471