Diamondfish
Monodactylus argenteus
Illustration: Bloom by Day
A flat silver diamond as tall as it is long, with dusky leading edges and black tips to the dorsal and anal fins and pelvic fins so small they are easy to miss. It schools under jetties and around pylons in estuaries — The Spit and the Seaway are full of them — and hangs in the shade.
how to recognise it
- a silver diamond, as tall as it is long
- black to dusky leading edges on the dorsal and anal fins, with blackish tips
- tiny pelvic fins
- small juveniles have a yellow dorsal fin and two vertical bars on the head
don’t confuse with
- Roundface batfish — the batfish is a taller disc with a dark bar through the eye, another over the pectoral and a black smudge beneath it
Field marks read from Fishes of Australia, 2026-10-16. Our wording, their facts. Max size 27 cm SL.
facts
- habitat
- estuary
- size
- ~18 cm, to 27 cm
Max size from Fishes of Australia (27 cm SL); the typical size is Bluebird’s, not from a cited source
- records near here
- 73 at 3 of 6 spots
A count of occurrence records near these spots, 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
no QLD rule listed — check before you dive
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.