Ostorhinchus moluccensis
Small reef cardinalfish logged across the Visayas, Sulawesi and Dili, best spotted hovering near coral crevices in 26-29C water.
A small, slim-bodied cardinalfish around 6cm, with a stocky head and large dark eyes typical of the family. Look for a muted brownish to reddish body tone with faint horizontal striping and a dusting of fine spots rather than bold bars. It hangs nearly motionless close to structure, which combined with its small size and subtle markings is often the clearest giveaway.
Divers typically find it hovering in small, loose groups close to coral heads, ledges or rubble patches, staying still enough that a torch beam barely moves it. It is not shy exactly, just unremarkable in motion, holding station near shelter rather than roaming the open reef, and it is most often noticed on slower, close-focus dives rather than during a fast drift.
Like other cardinalfish, males of this genus are mouthbrooders, carrying fertilised eggs in their mouths until the young are ready to disperse, so a male seen with a visibly swollen jaw may simply be minding a brood rather than feeding.
Sighting data shows no clear season, and with a comfortable range of 26 to 29.3C it is present on these reefs year-round rather than tied to a particular month.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
Most reliably logged in the Philippines, especially across the Visayas, with strong showings in Sulawesi and Bali in Indonesia and around Dili in Timor-Leste. A single Malaysian record comes from Sabah, making this largely a Coral Triangle fish rather than a wide-ranging one.
Mapping where Moluccan Cardinalfish is logged…
It shows up most often in the Philippine Visayas, with further sightings across Sulawesi and Bali in Indonesia and near Dili in Timor-Leste. It is considered an uncommon find at most of these sites rather than something you are guaranteed to see.
There is no strong seasonal pattern in the sighting data, and it tolerates a warm 26 to 29.3C range typical of Coral Triangle reefs year-round, so timing your trip around this species specifically is not necessary.
Check for a small, roughly 6cm cardinalfish with a stocky head, big eyes and a brownish to reddish body carrying faint stripes and fine speckling rather than bold bands. It usually sits still near coral cover, which helps separate it from more actively swimming look-alikes.
They stay small, reaching around 6cm, which is typical for reef-dwelling cardinalfish in this family.
No. They are harmless, small reef fish that pose no risk to divers and simply hold position near shelter as you pass.
As with other cardinalfish, males carry the fertilised eggs in their mouths until they hatch, a strategy called mouthbrooding that protects the brood from predators on the reef.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
Iridescent Cardinalfish
1,784 sites
