Blind tassel-fish

Eleutheronema tetradactylum, the fourfinger threadfin, known as rawas in India is a species of marine ray-finned fish, a threadfin from the family Polynemidae which occurs in the Indian and western Pacific Ocean.

Habitat

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 mullets, anchovies and drums, 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 copepods and mysids although they also feed on small decapods while larger juveniles feed prawns and mysids. This species is a protandrous hermaphrodite and Australian studies found that they were males at fork length of 24–47 centimetres (9.4–18.5 in), hermaphrodites at fork lengths between 25–46 centimetres (9.8–18.1 in) FL and females are found at fork lengths of 28–72 centimetres (11–28 in). Off the northeast coast of Queensland, most of the fish with fork lengths greater than 45–50 centimetres (18–20 in) 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.

Distribution

Eleutheronema tetradactylum has an Indo-Pacific distribution and ranges from the Persian Gulf to Australia and Papua New Guinea.