Threadfin Fish: ID, Species, Taste and Why It Costs More

A threadfin is a coastal fish of the family Polynemidae, named for the long, separate thread-like rays that hang below each pectoral fin. Wikipedia counts nine genera and about 40 species, from the 11 cm dwarf threadfin to species reaching 2 m. They are important commercial food fish and popular with anglers (Wikipedia).

What does threadfin mean? It is a plain description: the lower part of the pectoral fin is split into three to seven free rays that look like threads. The common names of several species count those threads, as in fourfinger and sixfinger threadfin.

One name clash to know about: Threadfin is also the name of a piece of software, an M3U proxy for Plex, Jellyfin and Emby based on xTeVe (GitHub). This page is about the fish.

Four features together make a threadfin easy to recognise (Wikipedia):

• Threads under the pectoral fin: the fin is in two parts, and the lower part is three to seven long, independent rays
• Mouth underneath: a blunt, rounded snout overhangs a mouth set low on the head
• Two dorsal fins, far apart
• A large, deeply forked tail built for speed

Threadfins live in open, shallow water over mud, sand or silt, and they tolerate a wide range of salinity, so you will meet them on beaches, in estuaries and sometimes in rivers. They eat crustaceans and smaller fish. When you photograph one, lift and spread the pectoral fin: the number of free rays is the quickest way to narrow down the species.

• Fourfinger threadfin, Eleutheronema tetradactylum: the big one in Asian markets. Wikipedia gives a maximum of 2 m (6.6 ft), with 50 cm more normal, and a range from the Persian Gulf to Australia and Papua New Guinea; FishBase records a maximum weight of 145 kg. Local names include rawas in India and blue threadfin in Australia (Wikipedia). In Singapore, threadfin is sold under the names ngor he and ikan kurau (NTUC FairPrice).
• Sixfinger threadfin or moi, Filistriatus (formerly Polydactylus) sexfilis: a Hawaiian fish up to 61 cm and 3.2 kg. Wikipedia notes that in pre-colonial Hawaii moi was reserved for royalty and farmed in special ponds, and it is still farmed in Hawaii today.
• Giant African threadfin: Wikipedia names it with the fourfinger threadfin as one of the largest species.

Threadfins also change sex. The fourfinger threadfin is protandrous, meaning fish mature as males first (Wikipedia). The sixfinger threadfin starts as a male at 20 to 25 cm fork length and becomes a female at 30 to 40 cm (Wikipedia). So the biggest fish in a catch are more likely to be females.

They are different fish. The threadfin shad (Dorosoma petenense) is a small freshwater forage fish from the southeastern United States, most only about 1 inch long and adults 7 to 8 inches (Wikipedia). It is a forage fish eaten by striped bass, largemouth bass and catfish, which is why anglers use it as bait, and mass die-offs happen when water drops below 42F (Wikipedia). Its "thread" is an elongated dorsal fin, not free rays under the pectoral fin. If your fish came from a US lake or reservoir and is small and silvery, it is almost certainly a shad, not a threadfin.

Threadfin is an established food fish: Wikipedia calls the family important to commercial fisheries as food, and the fourfinger threadfin is sold fresh, frozen, dried and salted and farmed in Asia. NTUC FairPrice describes its frozen portions as suited to steaming, pan-frying or grilling.

FishBase gives these estimated nutrient values for fourfinger threadfin per 100 g of raw flesh:

• Protein: about 20% (range 18 to 22)
• Omega-3: about 0.122 g (range 0.065 to 0.224)
• Selenium: about 52.9 micrograms
• Calcium: about 38.1 mg
• Iron: about 0.744 mg

On mercury, we did not find threadfin on the US FDA fish list. The Singapore Food Agency advises limiting predatory fish such as swordfish, shark, king mackerel, tilefish and bigeye tuna, and threadfin is not on that list. If you are pregnant, feeding young children or eating fish you caught yourself, follow your local food agency's fish advice and any advisory for that water.

Because demand is high and the big wild fish are under pressure. The sources point to three reasons:

• It is a prized fish: FishBase puts the fourfinger threadfin in its "High" price category and rates it highly commercial, and Wikipedia says it commands premium prices in parts of Asia, especially Kuwait and Iran.
• Wild stocks are vulnerable: FishBase scores its vulnerability to fishing at 69 out of 100 (high to very high) and its climate vulnerability at 91 out of 100, and Wikipedia reports it is listed as Endangered in the Persian Gulf, where populations are declining fast.
• Farming only partly fills the gap: fourfinger and sixfinger threadfin are both farmed (Wikipedia), and the cheaper frozen imported portions in supermarkets are a different product from fresh, large wild fish.

As a price snapshot, on 25 September 2026 NTUC FairPrice in Singapore sold a 160 g frozen portion from Vietnam for S$5.00 on offer, down from S$7.90. That works out to about S$31 a kilogram on offer and about S$49 a kilogram at the normal price.

FishLens identifies fish from a photo. For a threadfin, take one photo side-on and a second with the pectoral fin lifted so the free rays show, then count them. Anglers in the US Southeast should also compare their catch with the threadfin shad above before calling it a threadfin. For more general tips, see key features to identify fish.

Research and drafting for this page were assisted by AI and checked line by line against the sources listed below. Every number names the organisation it comes from, and where sources disagree we say so instead of picking one silently. Prices are shop listings we checked on 25 September 2026; they change, so confirm before you rely on them. If you find an error, tell us and we will correct it.