Threadfin (Blue and King Threadfin)
Surf / EstuaryThe threadfins of WA's tropical north — blue threadfin and the larger king threadfin — named for the trailing thread-like filaments below the pectoral fin. Prized inshore sportfish of the Pilbara and Kimberley beaches, creek mouths and estuaries, hunting prawn and baitfish on the run-in tide. Soft mouths, fine eating, and a fixture of any northern beach session.
Overview
Threadfin are the great inshore prize of tropical WA — two species that share the same waters and the same trailing pectoral filaments that give the family its name. Blue threadfin (Eleutheronema tetradactylum, also called blue salmon or Cooktown salmon) are the smaller, more common of the two; king threadfin (Polydactylus macrochir) grow to well over a metre. Both patrol surf gutters, sand flats, creek mouths and estuary channels from the Pilbara through Eighty Mile Beach and into the Kimberley, hunting prawn, mullet and small baitfish on the rising tide. They have notably soft mouths — a soft strike and steady pressure beat a hard hookset — and they're among the best eating fish of the North Coast. Eighty Mile Beach is the iconic shore-based threadfin fishery.
Identification
Threadfin salmon, threadie, blue salmon, king salmon, Cooktown salmon
Three names, two fish. 'Threadfin' covers both; 'blue salmon' means the blue threadfin (Eleutheronema tetradactylum); 'king threadfin' or 'king salmon' means the larger Polydactylus macrochir. Neither is a salmon. Both share the family marker — free, thread-like filaments trailing below the pectoral fin, used to feel for prey in muddy water. Count them: blue threadfin has four, king threadfin has five, and that's the reliable separation in the hand. Blue threadfin are the smaller, brighter fish with a bluish-yellow cast to the fins; king threadfin are longer, heavier through the shoulders, more uniformly silver-bronze, and grow well past a metre.
How to Catch
Live mullet, prawn, fresh mullet fillet, herring, strip baits
Soft plastics on 1/4–1/2oz jigheads, suspending hardbodies, soft vibes, slow-rolled paddle-tail plastics
Running sinker rig with a 4/0–5/0 circle hook and 30–40lb fluorocarbon leader on the beach, with enough lead to hold in the surf. From a boat or creek bank, a lighter unweighted live-bait rig on the run-in tide. Keep drag moderate — soft mouths tear out under heavy load.
On the beaches, find a deeper gutter close to the sand and fish baits or plastics across the rising tide. In the creeks, cast plastics and hardbodies into the run-out at change of light, working them slowly along the sandbank edges. Feed line briefly on the take rather than striking hard, then lift into the fish and keep steady pressure. Net or slide them on the beach — lifting by the line tears the hook from their soft mouths.
April through November is prime, covering the fishable dry-season window. Run-in tides in the last hour before high are the standout, with the first of the run-out also good. Dawn, dusk and the new and full moons produce the best of it.
Blue to ~1m; king to 1.5m and 20kg, commonly 60–90cm
Apr–Nov (dry season peak)
Size & Growth
Blue threadfin are the everyday fish: commonly 40–70cm and up to about 3kg, reaching around a metre at the extreme. King threadfin are the bigger prize — commonly 60–90cm, with fish over a metre and into the mid-teens of kilos genuinely on the cards, and a maximum around 1.5m and 20kg. A good northern beach session might produce a bag of blues at 50–60cm and one solid king. Both grow quickly in the warm north. King threadfin also change sex as they grow, so the big fish are females — worth knowing when you're deciding what to keep and what to slide back.
Diet & Habitat
Threadfin hunt prawn, mullet and small baitfish in turbid, shallow water, using those pectoral filaments to feel out prey where they can't see it — which is why they thrive in the muddy tidal water of the north. They work surf gutters, sand and mud flats, creek mouths, mangrove drains and estuary channels, moving up onto the flats with the run-in tide and dropping back with it. In WA that's the tropical north: the Pilbara beaches and back creeks around Onslow, Dampier and Karratha, the De Grey and Port Hedland, Eighty Mile Beach, and the Kimberley creeks and Cambridge Gulf around Wyndham. Both species overlap through the same water.
WA Size & Bag Limits
| Minimum size | 45 cm (king threadfin); no minimum for blue and other threadfin |
|---|---|
| Bag limit | 2 (king threadfin); 4 (blue and other threadfin) |
| Counts toward | Both count within the statewide nearshore/estuarine finfish mixed daily bag of 16. |
King threadfin (Polydactylus macrochir): minimum size 450mm, bag limit 2. Other threadfin species including blue threadfin: no minimum size, bag limit 4. Both sit within the statewide nearshore/estuarine finfish mixed daily bag of 16.
Eating Quality
Excellent — moist, white, mild flesh with a firm flake that holds together grilled, pan-fried, baked or crumbed. Among the better eating fish of the North Coast, on a par with mulloway and better than most of what else comes off a northern beach. Bleed and ice on capture; the tropical heat is unforgiving and an hour on the sand costs you real quality. Smaller blue threadfin arguably eat better than a big king — finer flesh, fillets of a sensible thickness — while a large king gives thick loins that suit cutlets, baking whole or a curry. Skin the fillets; the skin is thick and does nothing for the dish. Vacuum-sealed it freezes well for a white fish, which is worth knowing on a long trip north.
Perth Tips
Eighty Mile Beach Caravan Park is the classic base for shore-based threadfin, with the run-in tides on the new and full moons producing best. Beadon Creek (Onslow), the Pilbara back creeks, and the Cambridge Gulf creeks around Wyndham and Kununurra all hold fish. Don't over-strike — feed line on the take, then lift. Watch for crocs in the creeks north of Broome.