Threadfins are silvery grey ray-finned fish of the family Polynemidae. Found in tropical to subtropical waters throughout the world, the threadfin family contains nine genera and about 40 species. A distantly related species sometimes known by the name threadfin, Scyris indica, is properly the Indian threadfish (family Carangidae).

Ranging in length from in the dwarf threadfin (Parapolynemus verekeri) to in fourfinger threadfin (Eleutheronema tetradactylum) and giant African threadfin (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.

thumb|left|200px| Filistriatus sexfilis or moi (sixfinger threadfins), were reserved for Hawaiian royalty or the [[aliʻi<!--ali'i-->.

Genera and species

thumb|[[Fourfinger threadfin (Eleutheronema tetradactylum)]]

thumb|[[Sevenfinger threadfin (Filimanus heptadactyla)]]

thumb|[[Elegant paradise fish (Polynemus multifilis)]]

The family includes 43 species in nine genera:

  • Genus Eleutheronema
  • Eleutheronema rhadinum <small>(Jordan & Evermann, 1902)</small> (East Asian fourfinger threadfin)
  • Eleutheronema tetradactylum <small>(Shaw, 1804)</small> (Fourfinger threadfin)
  • Eleutheronema tridactylum <small>(Bleeker, 1849)</small> (Threefinger threadfin)
  • Genus Filimanus
  • Filimanus heptadactyla <small>(Cuvier, 1829)</small> (Sevenfinger threadfin)
  • Filimanus hexanema <small>(Cuvier 1829)</small> (Javanese threadfin)
  • Filimanus perplexa <small>Feltes 1991</small> (Splendid threadfin)
  • Filimanus sealei <small>(Jordan & Richardson, 1910)</small> (Eightfinger threadfin)
  • Filimanus similis <small>Feltes 1991</small> (Indian sevenfinger threadfin)
  • Filimanus xanthonema <small>(Valenciennes, 1831)</small> (Yellowthread threadfin)
  • Genus Filistriatus)
  • Polydactylus approximans <small>(Lay & Bennett, 1839)</small> (Blue bobo)
  • Polydactylus luparensis <small>Lim, Motomura & Gambang, 2010</small> (Sarawak giant threadfin)
  • Polydactylus macrochir <small>(Günther, 1867)</small> (King threadfin)
  • Polydactylus macrophthalmus <small>(Bleeker, 1858)</small> (River threadfin)
  • Polydactylus malagasyensis <small>Motomura & Iwatsuki, 2001</small> (African blackspot threadfin)
  • Polydactylus microstomus <small>(Bleeker, 1851)</small> (Smallmouth threadfin)
  • Polydactylus mullani <small>(Hora, 1926)</small> (Arabian blackspot threadfin)
  • Polydactylus multiradiatus <small>(Günther, 1860)</small> (Australian threadfin)
  • Polydactylus nigripinnis <small>Munro, 1964</small> (Blackfin threadfin)
  • Polydactylus octonemus <small>(Girard, 1858)</small> (Atlantic threadfin)
  • Polydactylus oligodon <small>(Günther, 1860)</small> (Littlescale threadfin)
  • Polydactylus opercularis <small>Seale & Bean, 1907</small> (Yellow bobo)
  • Polydactylus persicus <small>Motomura & Iwatsuki, 2001</small> (Persian blackspot threadfin)
  • Polydactylus quadrifilis <small>(Cuvier, 1829)</small> (Giant African threadfin)
  • Polydactylus sextarius <small>(Bloch & Schneider, 1801)</small> (Blackspot threadfin)
  • Polydactylus virginicus <small>(Linnaeus, 1758)</small> (Barbu)
  • Genus Polynemus
  • Polynemus aquilonaris <small>Motomura, 2003</small> (Northern paradise fish)
  • Polynemus bidentatus <small>Motomura & Tsukawaki, 2006</small>
  • Polynemus dubius <small>Bleeker, 1854</small> (Eastern paradise fish)
  • Polynemus hornadayi <small>Myers, 1936</small> (Hornaday's paradise fish)
  • Polynemus kapuasensis <small>Motomura & van Oijen, 2003</small> (Kapuas elegant paradise fish)
  • Polynemus melanochir <small>Valenciennes, 1831</small> (Blackhand paradise fish)
  • Polynemus multifilis <small>Temminck & Schlegel, 1843</small> (Elegant paradise fish)
  • Polynemus paradiseus <small>Linnaeus, 1758</small> (Paradise threadfin)

Phylogeny

The following cladogram is from Girard & Chovanec (2025):

  • Fisheries Western Australia - Threadfins Fact Sheet
  • The Paradise threadfin, Polynemus paradiseus
  • Offshore aquaculture project yields a traditional Hawaiian delicacy

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