Threadfin

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.

Polydactylus sexfilis or moi (sixfinger threadfins),[3] were reserved for Hawaiian royalty or the aliʻi.[4] .

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.

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.

In Hawaii, sixfinger threadfins are the subject of commercial open-ocean cage mariculture.[5][6]

Fourfinger threadfin (Eleutheronema tetradactylum)

Sevenfinger threadfin (Filimanus heptadactyla)

Elegant paradise fish (Polynemus multifilis)

The species in eight genera are:

• Genus Eleutheronema
  • Eleutheronema rhadinum (Jordan & Evermann, 1902) (East Asian fourfinger threadfin)
  • Eleutheronema tetradactylum (Shaw, 1804) (Fourfinger threadfin)
  • Eleutheronema tridactylum (Bleeker, 1849) (Threefinger threadfin)

• Genus Filimanus
  • Filimanus heptadactyla (Cuvier, 1829) (Sevenfinger threadfin)
  • Filimanus hexanema (Cuvier 1829) (Javanese threadfin)
  • Filimanus perplexa Feltes 1991 (Splendid threadfin)
  • Filimanus sealei (Jordan & Richardson, 1910) (Eightfinger threadfin)
  • Filimanus similis Feltes 1991 (Indian sevenfinger threadfin)
  • Filimanus xanthonema (Valenciennes, 1831) (Yellowthread threadfin)

• Genus Galeoides
  • Galeoides decadactylus (Bloch, 1795) (Lesser African threadfin)

• Genus Leptomelanosoma
  • Leptomelanosoma indicum (Shaw, 1804) (Indian threadfin)

• Genus Parapolynemus
  • Parapolynemus verekeri (Saville-Kent, 1889) (Dwarf paradise fish)

• Genus Pentanemus
  • Pentanemus quinquarius (Linnaeus, 1758) (Royal threadfin)

• Genus Polydactylus
  • Polydactylus approximans (Lay & Bennett, 1839) (Blue bobo)
  • Polydactylus bifurcus Motomura, Kimura & Iwatsuki, 2001 (Slender fivefinger threadfin)
  • Polydactylus longipes Motomura, Okamoto & Iwatsuki, 2001 (Long-limb threadfin)
  • Polydactylus luparensis Lim, Motomura & Gambang, 2010 (Sarawak giant threadfin)
  • Polydactylus macrochir (Günther, 1867) (King threadfin)
  • Polydactylus macrophthalmus (Bleeker, 1858) (River threadfin)
  • Polydactylus malagasyensis Motomura & Iwatsuki, 2001 (African blackspot threadfin)
  • Polydactylus microstomus (Bleeker, 1851) (Smallmouth threadfin)
  • Polydactylus mullani (Hora, 1926) (Arabian blackspot threadfin)
  • Polydactylus multiradiatus (Günther, 1860) (Australian threadfin)
  • Polydactylus nigripinnis Munro, 1964 (Blackfin threadfin)
  • Polydactylus octonemus (Girard, 1858) (Atlantic threadfin)
  • Polydactylus oligodon (Günther, 1860) (Littlescale threadfin)
  • Polydactylus opercularis Seale & Bean, 1907 (Yellow bobo)
  • Polydactylus persicus Motomura & Iwatsuki, 2001 (Persian blackspot threadfin)
  • Polydactylus plebeius (Broussonet, 1782) (Striped threadfin)
  • Polydactylus quadrifilis (Cuvier, 1829) (Giant African threadfin)
  • Polydactylus sexfilis (Valenciennes, 1831) (Sixfinger threadfin)
  • Polydactylus sextarius (Bloch & Schneider, 1801) (Blackspot threadfin)
  • Polydactylus siamensis Motomura, Iwatsuki & Yoshino, 2001 (Largemouth striped threadfin)
  • Polydactylus virginicus (Linnaeus, 1758) (Barbu)

• Genus Polynemus
  • Polynemus aquilonaris Motomura, 2003 (Northern paradise fish)
  • Polynemus bidentatus Motomura & Tsukawaki, 2006
  • Polynemus dubius Bleeker, 1854 (Eastern paradise fish)
  • Polynemus hornadayi Myers, 1936 (Hornaday's paradise fish)
  • Polynemus kapuasensis Motomura & van Oijen, 2003 (Kapuas elegant paradise fish)
  • Polynemus melanochir Valenciennes, 1831 (Blackhand paradise fish)
  • Ploynemus multifilis Temminck & Schlegel, 1843 (Elegant paradise fish)
  • Polynemus paradiseus Linnaeus, 1758 (Paradise threadfin)

• 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.

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