Threadfins are silvery grey
perciformfish of the
familyPolynemidae. Found in tropical to subtropical waters throughout the world, the threadfin family contains eight
genera and about 40
species.[2] An unrelated species sometimes known by the name threadfin, Alectis indicus, is properly the
Indian threadfish (family
Carangidae).
Ranging in length from 11 cm (4.5 in) in the
dwarf threadfin (Parapolynemus verekeri) to 2 m (6.6 ft) 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.
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
Greekpoly 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 can 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.
Reproduction
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.
^Suryanata, Krisnawati; Umemoto, Karen N. (2005). "Tension at the nexus of the global and local: culture, property, and marine aquaculture in Hawai'i". Environment and Planning A. 35 (2): 199, 206.
CiteSeerX10.1.1.456.680.
doi:
10.1068/a35116.
S2CID143928957.