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threadfin
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 in the black-finned threadfin (''Polydactylus nigripinnis'') to 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.
==Description==
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.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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