''Eleutheronema tetradactylum'', the fourfinger threadfin, is a species of marine ray-finned fish, a threadfin from the family

Polynemidae Threadfins are silvery grey perciform fish of the family Polynemidae. Found in tropical to subtropical waters throughout the world, the threadfin family contains eight genera and about 40 species. An unrelated species sometimes known by the name ...

which occurs in the Indian and western Pacific Ocean.

Description

''Eleutheronema tetradactylum'' has two dorsal fins; the first has 9 spines and the second has 13–15 soft rays, with 13 being the mean. The

anal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

has 3 spines and 14–19 soft rays. The pectoral fins have 16–18 rays, and there are 4 pectoral filaments. The upper sides of the head and body have a slight darkish silver tinge, lighting in the lower flanks. Both dorsal fins show a blackish anterior margin, with the remaining parts of the fins translucent and slightly dusky. The membranes of the pectoral fins are vivid yellow in smaller individuals, but in larger fish this becomes duskier. The pectoral filaments are white. The pelvic fins are white with a yellow front edge, while the caudal fin is blackish with a yellowish base. This species can attain a maximum total length of , although is a more normal size.

Distribution

''Eleutheronema tetradactylum'' has an

Indo-Pacific The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the ...

distribution and ranges from the Persian Gulf to Australia and Papua New Guinea,

Habitat and biology

''Eleutheronema tetradactylum'' adults show a preference for shallow muddy substrates in coastal waters and they may enter rivers. The juveniles occur in estuaries. In the winter the adults move up rivers. It is normally observed in loose schools, but larger fish are more often recorded as pairs or individuals. It is a carnivorous species which preys on prawns and fish. The fish preyed upon are mainly

grey mullet Grey mullet can mean any of several fish in the family ''Mugilidae'' (the mullets) and having a greyish hue: * Flathead grey mullet, ''Mugil cephalus'' * Thicklip grey mullet, ''Chelon labrosus'' * Boxlip grey mullet, ''Oedalechilus labeo'' * Leapi ...

s, anchovies and

drums A drum kit (also called a drum set, trap set, or simply drums) is a collection of drums, cymbals, and other Percussion instrument, auxiliary percussion instruments set up to be played by one person. The player (drummer) typically holds a pair o ...

, and they sometimes feed on polychaetes. The ratio of crustaceans to fish fed on varies with the season. The small larvae have a diet dominated by

copepod Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...

s and mysids although they also feed on small decapods while larger juveniles feed prawns and mysids. This species is a

protandrous hermaphrodite Sequential hermaphroditism (called dichogamy in botany) is a type of hermaphroditism that occurs in many fish, gastropods, and plants. Sequential hermaphroditism occurs when the individual changes its sex at some point in its life. In particular, ...

and Australian studies found that they were males at fork length of , hermaphrodites at fork lengths between FL and females are found at fork lengths of . Off the northeast cost of Queensland, most of the fish with fork lengths greater than are females. The hermaphroditic fish form once they reach 1- to 2-year-old, and then females begin to appear at 2-3-years old. It is thought that the males change to hermaphrodites just after spawning in April and May and they remain in a hermaphroditic state until the next breeding season is over. They then progress from hermaphrodites to females before the breeding season after that. The larval stage is little known but it is known that lower estuaries, tidal swamps and lagoons, and the shallows along the foreshores are used as nursery areas.

Usage

''Eleutheronema tetradactylum'' is marketed fresh, frozen, and dried or salted. This species is also used in

aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...

. This species is one of an important commercial quarry for fisheries in Kuwait and the species is also taken as

bycatch Bycatch (or by-catch), in the fishing industry, is a fish or other marine species that is caught unintentionally while fishing for specific species or sizes of wildlife. Bycatch is either the wrong species, the wrong sex, or is undersized or juve ...

. They are one of the more expensive fish in the Kuwaiti and Iranian markets.

Conservation

''Eleutheronema tetradactylum'' has not had its global conservation status evaluated by the IUCN but it has been classified as Endangered in the Persian Gulf where the population appears to be in a rapid decline.

Common names

''Eleutheronema tetradactylum'' is a widespread and commercially important species and, as such, has a number of English

common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often contrast ...

s, other than the fourfinger threadfin. In Australia it is known as the blue threadfin, although other names include blind tassel-fish, blue salmon, bluenose salmon, blunt-nosed salmon, burnett salmon, Colonial salmon, Cooktown salmon, giant threadfin, kingfish, Rockhampton kingfish, Rockhampton salmon, tassel-fish and threadfin. In India names used include Gurjali fish in Bengali,https://fishluxury.com/salmon-fish-in-bengali/ Indian salmon, white salmon, row ball and horse's friend.

References

{{DEFAULTSORT:Eleutheronema Tetradactylum Polynemidae Taxa named by George Shaw Fish described in 1804 Taxobox binomials not recognized by IUCN