Ostorhinchus sealei
Small, uncommon cardinalfish spotted around Sulawesi and Raja Ampat reefs at 27.6 to 29.3 C, year-round in Indonesia's warm shallows.
A small, slim-bodied cardinalfish reaching about 7 cm, with a pale silvery to tan body marked by a dark stripe running through the eye and a second dark bar near the tail base. Look for the two large, dark eyes typical of the group and a slightly translucent look to the body under torchlight. It hovers close to structure rather than out in the open, which helps separate it from busier reef fish nearby.
Usually seen hovering singly or in loose small groups tucked against coral heads, rubble patches or overhangs rather than swimming in open water. Like most cardinalfish it stays fairly still and lets divers approach slowly, becoming more active as light fades towards dusk. Expect to find it at a measured, patient look rather than a quick swim-by, since it is logged as uncommon even at the sites where it turns up.
Cardinalfish in this genus are mouth-brooders, with males carrying the fertilised eggs in their mouths until the young hatch, so a male you spot with a visibly swollen jaw may be guarding a brood rather than feeding.
No clear season shows up in the sightings, and warm water year-round (27.6 to 29.3 C) means it stays on Indonesian reefs in every month divers have logged it.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
Logged almost exclusively in Indonesia, with the strongest showing around Sulawesi and single confirmed sites in Raja Ampat and Nusa Tenggara. If you are hunting for it, Sulawesi's reefs currently offer the best odds.
Mapping where Seale's Cardinalfish is logged…
Sightings cluster in Indonesia, particularly around Sulawesi, with additional records from Raja Ampat and Nusa Tenggara. It has not been logged widely outside these regions so far.
There is no strong seasonal pattern in the sightings, and warm water year-round on Indonesian reefs means it can turn up in any month.
Look for a small, slender cardinalfish around 7 cm with a dark stripe through the eye, a dark bar near the tail, and large dark eyes. It tends to hover near coral heads or rubble rather than swim in open water.
They stay small, typically around 7 cm long, which is fairly typical for cardinalfish on Indo-Pacific reefs.
Like other cardinalfish, males of this species are thought to mouth-brood, holding fertilised eggs in their mouth until the young are ready to hatch. A male doing this will look like he has an oddly swollen jaw.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
Iridescent Cardinalfish
1,784 sites
