Blue threadfin
Eleutheronema tetradactylum (formerly Eleutheronema tetradactylus)
Illustration: Bloom by Day
A silvery, blunt-nosed estuary fish with the mouth underneath and FOUR white whisker-like filaments trailing below each pectoral fin, which it uses to feel through mud. Loose schools in turbid shallow water; count the filaments and the king threadfin is ruled out.
how to recognise it
- FOUR free filaments below the pectoral fin, the upper one longest, reaching back to the pelvic-fin base
- the filaments themselves are white
- the front edge of the pelvic fin is yellow
- the tail is yellowish at its base and blackish toward the outer parts
- an elongated, compressed silvery body with a blunt rounded snout and the mouth underneath
don’t confuse with
- King threadfin — the king threadfin is plain — no spots, no stripes — and its FOURTH filament is enormous, 40 to 53% of the body length; count the filaments and look at how far the long one reaches
Field marks read from FishBase, 2026-10-15. Our wording, their facts. Max size 200 cm TL.
facts
- habitat
- estuary
- size
- ~50 cm, to 200 cm
Max size from FishBase (200 cm TL); the typical size is Bluebird’s, not from a cited source
- records
- 564 at 10 spot(s), none of
them in this region
Recorded at Dunk Island (Mission Beach), Hinchinbrook Island — Ramsay Bay, Hinchinbrook Channel (West), Magnetic Island — Geoffrey Bay, Cid Harbour (Whitsunday — West), Pioneer Rocks (Whitsundays), Great Keppel Island (East), Great Keppel Island (West), Fraser Island — 75-Mile Beach, Redcliffe Jetty. A count of occurrence records, not abundance. Records are where someone looked.
when it has been recorded
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A gap means no record in the sample, not absence.
the rule
QLD — Min: 40cm · Limit: 10
source
· verified 2026-10-10
no NSW rule listed — check before you dive
no closed season recorded for this species — that is not the same as open; check the official page
Rules checked 2026-10-13 against qld.gov.au
Rules change. Check before you dive.
Occurrence data: Atlas of Living Australia (ala.org.au), CC-BY 4.0.
Diver transect counts: Reef Life Survey (reeflifesurvey.com), CC-BY 4.0, supplied via ALA.
Target and protected species: Queensland tidal-water size and possession limits (qld.gov.au) and NSW saltwater bag and size limits plus threatened species lists (dpird.nsw.gov.au).
Habitat and size: Bluebird, approximate, from general knowledge. Not cited. FishBase is CC BY-NC and this app is commercial, so it is not used.
Description written for Bloom. RECORDS ARE WHERE SOMEONE LOOKED, NOT WHERE THE FISH ARE. A record count is a count of records near here and nothing else -- it is not abundance, and a species with few records is not rare. Absence of records is not absence of fish.
Diver transect counts: Reef Life Survey (reeflifesurvey.com), CC-BY 4.0, supplied via ALA.
Target and protected species: Queensland tidal-water size and possession limits (qld.gov.au) and NSW saltwater bag and size limits plus threatened species lists (dpird.nsw.gov.au).
Habitat and size: Bluebird, approximate, from general knowledge. Not cited. FishBase is CC BY-NC and this app is commercial, so it is not used.
Description written for Bloom. RECORDS ARE WHERE SOMEONE LOOKED, NOT WHERE THE FISH ARE. A record count is a count of records near here and nothing else -- it is not abundance, and a species with few records is not rare. Absence of records is not absence of fish.