Selasa, 22 Maret 2011

oarfish

Oarfish are large, greatly elongated, pelagic Lampriform fishes comprising the small family Regalecidae.[1] 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 17 metres (56 ft) in length.[2][3]
The common name oarfish is presumably in reference to either their highly compressed and elongated bodies, or to the former (but now discredited) belief that the fish "row" themselves through the water with their pelvic fins.[4] 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, make oarfish a probable source of many sea serpent tales.
Although the larger species are considered game fish and are (to a minor extent) fished commercially, oarfish are rarely caught alive; their flesh is not well regarded due to its gelatinous consistency.

Contents

Anatomy and morphology

Oarfish that washed ashore on a Bermuda beach in 1860. The animal was 16 feet (4.9 m) long and was originally described as a sea serpent.
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 approximately 400 dorsal fin rays, the first 10 to 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 to 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. At least one account, from researchers in New Zealand, describes the oarfish as giving off "electric shocks" when touched.[4]
Like other members of its order, the oarfish has a small yet highly protrusible oblique mouth 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 meters (with unconfirmed reports of 15 meters or more) and 272 kilograms in weight. The streamer fish is known to reach 3 meters total length whilst the largest recorded specimen of Regalecus russelii measured just 540 centimeters standard length. It is probable that this little-known species can regularly reach a maximum length of at least 15.2 meters (50 ft).[citation needed]

Distribution

The members of the family are known to have a worldwide range. However, specific encounters with live individuals in situ are rare and distribution information is collated from records of oarfishes caught or washed ashore.[4]

Ecology and life history

Rare encounters with divers and accidental catches have supplied what little is known of oarfish behavior and ecology. Apparently solitary animals, oarfish may frequent significant depths up to 1,000 metres (3,300 ft). A photograph on display in bars, restaurants, guesthouses, and markets around Thailand that is captioned, "Queen of Nagas seized by American Army at Mekhong River, Laos Military Base on June 27, 1973 with the length of 7.80 meters," is a hoax. The photograph is actually that taken by Dr. Leo Smith (The Field Museum), of an oarfish found in late 1996 by US Navy SEAL trainees on the coast of Coronado, California.[5][6]
A catch of an 11 ft 4 in (3.3 metres), 140 lb (63.5kg) monster that turned out to be an oarfish was reported on 17 February 2003 by Ms Val Fletcher, who was using a fishing rod baited with squid, at Skinningrove, a coastal settlement of north-east England.[7]

[edit] Behavior

In 2001 an oarfish was filmed alive and in situ: the 1.5 meter 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 axis perpendicular to the ocean surface. In this posture the downstreaming light would silhouette the oarfishes' prey, making them easier to spot.
In July 2008, scientists captured footage of the rare fish swimming in its natural habitat off the Gulf of Mexico. It is the first ever confirmed sighting of an oarfish at depth, as most specimens are discovered dying at the sea surface or washed ashore. The fish was estimated to be between 5m and 10m in length.[8]
From December 2009 through March 2010, unusual numbers of the slender oarfish Regalecus russelii[9] (竜宮の使い “Ryūgū-No-Tsukai”,) known in Japanese folklore as the Messenger from the Sea God's Palace, have appeared in the waters and on the beaches of Japan; the appearance of which is said to portend earthquakes.[10]

[edit] Feeding ecology

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. Oarfish have no visible teeth.

Life history

The oceanodromous Regalecus glesne is recorded as spawning off Mexico from July to December; all species are presumed to be non-guarders and release brightly coloured, buoyant eggs, up to 6 millimetres (0.24 in) across, which are incorporated into the zooplankton. The eggs hatch after about three weeks into highly active larvae, that feed on other zooplankton. The larvae have little resemblance to the adults, with long dorsal and pelvic fins and extensible mouths.[4] Larvae and juveniles have been observed drifting just below the surface. In contrast, adult oarfish are rarely seen at the surface when not sick or injured.

[edit] Etymology and taxonomic history

Juvenile Regalecus glesne
The oarfish family contains four species in two genera.
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