Cantherhines sandwichiensis
Small and easy to miss: find Squaretail Filefish on Hawaii's reefs in 24.7-29C water, year-round, usually solo.
A small, laterally flattened fish that tops out around 13 cm, with a mottled brown to grey body that blends into rock and rubble. Look for the elongated, rounded body shape typical of filefish, a small mouth set low on the face, and a single thin dorsal spine tucked just behind the eye. It often hangs at odd angles or hovers close to structure rather than swimming openly, which is often the first clue you've spotted one rather than a similarly shaped reef fish.
Divers most often log it as an uncommon to rare find, tucked against rock ledges, rubble patches or coral heads rather than out in the open. It tends to hold its position or move in short bursts when approached, relying on camouflage more than speed, and doesn't school or gather in groups. Most sightings come from divers who are looking closely at reef structure rather than cruising past.
Like other filefish, it can lock itself into crevices using an erect dorsal spine, wedging its body so predators (and curious divers trying to get a closer look) can't easily pull it out.
Sightings show no clear seasonal pattern, and the observed temperature range of 24.7 to 29 C spans Hawaii's water temperatures nearly year-round, so there's no obvious month to prioritise.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
This one is a Hawaii specialty among the logged sightings, with sites across the islands making up the entire dataset so far. If you're diving Hawaii's rocky and coral reef mix, this is one of the small fish worth scanning ledges and rubble for.
Mapping where Squaretail Filefish is logged…
Logged sightings come almost entirely from Hawaii, making it a species to watch for on Hawaiian reef and rubble sites specifically rather than a fish you'd expect elsewhere in the tropical Pacific.
There's no detected season in the sighting data, and its comfort range of roughly 24.7 to 29 C covers Hawaii's water temperature most of the year, so it's realistic to look for it on any dive.
Look for a small, flattened, mottled brown fish around 13 cm long, hovering or wedged near rock and rubble rather than swimming in open water. Its low-set small mouth and single thin dorsal spine help separate it from similarly shaped reef fish.
They're a small species, typically reaching around 13 cm, so they're easy to overlook against a busy reef background.
No, they pose no threat to divers and will typically hold still or retreat into structure if approached.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
Cantherhines macrocerus
Whitespotted Filefish
664 sites
