|Atlantic threadfin, Polydactylus octonemus|
Threadfins are silvery grey perciform marine fish of the family Polynemidae. Found in tropical to subtropical waters throughout the world, the threadfin family contains nine genera and 33 species. An unrelated species sometimes known by the name threadfin, Alectis indicus, is properly the Indian threadfish (family Carangidae).
Ranging in length from 20 cm (7.9 in) in the black-finned threadfin (Polydactylus nigripinnis) to 200 cm (79 in) in fourfinger threadfins (Eleutheronema tetradactylum) and giant African threadfins (Polydactylus quadrifilis), threadfins are both important to commercial fisheries as a food fish, and popular among anglers. Their habit of forming large schools makes the threadfins a reliable and economic catch.
Their bodies are elongated and fusiform, with spinous and soft dorsal fins widely separated. Their tail fins are large and deeply forked; indicating speed and agility. The mouth is large and inferior; a blunt snout projects far ahead. The jaws and palate possess bands of villiform (fibrous) teeth. Their most distinguishing feature is their pectoral fins: they are composed of two distinct sections, the lower of which consists of three to seven long, thread-like independent rays. Polynemus species may have up to 15 of these modified rays.
In some species, such as the royal threadfin (Pentanemus quinquarius), the thread-like rays may extend well past the tail fin. This feature explains both the common name threadfin and the family name Polynemidae, from the Greek poly meaning "many" and nema meaning "filament". Similar species, such as the mullets (family Mugilidae) and milkfish (family Chanidae) can be easily distinguished from threadfins by their lack of filamentous pectoral rays.
Distribution and habitat
Threadfins frequent open, shallow water in areas with muddy, sandy, or silty bottoms; they are rarely seen at reefs. Their pectoral rays are thought to serve as tactile structures, helping to find prey within the sediments. Noted for being euryhaline, threadfins are able to tolerate a wide range of salinity levels. This attribute allows threadfins to enter estuaries and even rivers. They feed primarily on crustaceans and smaller fish.
Presumed to be pelagic spawners, threadfins probably release many tiny, buoyant eggs into the water column, which then become part of the plankton. The eggs float freely with the currents until hatching.
Threadfin has been used as an ingredient in creating crab stick.
The species in eight genera are:
- Genus Eleutheronema
- Genus Filimanus
- Sevenfinger threadfin, F. heptadactyla (Cuvier, 1829).
- Javanese threadfin, F. hexanema (Cuvier, 1829).
- Splendid threadfin, F. perplexa Feltes, 1991.
- Eightfinger threadfin, F. sealei (Jordan & Richardson, 1910).
- Indian sevenfinger threadfin, F. similis Feltes, 1991.
- Yellowthread threadfin, F. xanthonema (Valenciennes, 1831).
- Genus Galeoides
- Genus Leptomelanosoma
- Indian threadfin, L. indicum (Shaw, 1804).
- Genus Parapolynemus
- Genus Pentanemus
- Genus Polydactylus
- Blue bobo, P. approximans (Lay & Bennett, 1839).
- Slender fivefinger threadfin, P. bifurcus Motomura, Kimura & Iwatsuki, 2001.
- Long-limb threadfin, P. longipes Motomura, Okamoto & Iwatsuki, 2001.
- King threadfin, P. macrochir (Günther, 1867).
- River threadfin, P. macrophthalmus (Bleeker, 1858).
- African blackspot threadfin, P. malagasyensis Motomura & Iwatsuki, 2001.
- Small-mouthed threadfin, P. microstomus (Bleeker, 1851).
- Arabian blackspot threadfin, P. mullani (Hora, 1926).
- Australian threadfin, P. multiradiatus (Günther, 1860).
- Black-finned threadfin, P. nigripinnis Munro, 1964.
- Atlantic threadfin, P. octonemus (Girard, 1858).
- Littlescale threadfin, P. oligodon (Günther, 1860).
- Yellow bobo, P. opercularis Seale & Bean, 1907.
- Persian blackspot threadfin, P. persicus Motomura & Iwatsuki, 2001.
- Striped threadfin, P. plebeius (Broussonet, 1782).
- Giant African threadfin, P. quadrifilis (Cuvier, 1829).
- Sixfinger threadfin, P. sexfilis (Valenciennes, 1831).
- Blackspot threadfin, P. sextarius (Bloch & Schneider, 1801).
- Largemouth striped threadfin, P. siamensis Motomura, Iwatsuki & Yoshino, 2001.
- Barbu, P. virginicus (Linnaeus, 1758).
- Genus Polynemus
- Northern paradise fish, P. aquilonaris Motomura, 2003.
- P. bidentatus Motomura & Tsukawaki, 2006.
- Eastern paradise fish, P. dubius Bleeker, 1854.
- Hornaday's paradise fish, P. hornadayi Myers, 1936.
- Elegant paradise fish, P. multifilis Temminck & Schlegel, 1843.
- Paradise threadfin, P. paradiseus Linnaeus, 1758.
Timeline of genera
This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (November 2008) (Learn how and when to remove this template message)
- Froese, Rainer, and Daniel Pauly, eds. (2006). "Polynemidae" in FishBase. January 2006 version.
- Sepkoski, Jack (2002). "A compendium of fossil marine animal genera". Bulletins of American Paleontology. 364: 560. Archived from the original on 2009-02-20. Retrieved 2011-05-19.