Ostorhinchus parvulus
A small reef-hider common across Sabah and Raja Ampat, best spotted tucked in coral crevices year-round in warm 25-29C water.
A tiny fish, only around 3cm, with a slim, big-eyed cardinalfish body and a translucent to pale tan colouring. The giveaway mark is a small dark spot rimmed in reddish colour near the base of the tail, which separates it from plainer-bodied relatives. It typically hangs motionless just above or beside coral rubble rather than swimming in the open.
Divers typically find it hovering close to shelter, tucked near coral branches, rubble, or small crevices rather than out over open reef. It stays fairly still and low-key when divers approach, more likely to be overlooked than to bolt, which is part of why it's logged as uncommon even where it lives. Look for it during the day at typical recreational depths on mixed coral and rubble reef.
Like other cardinalfish, it's a mouthbrooder, with the male carrying fertilised eggs in his mouth until they hatch, a detail worth knowing if you spot one with an oddly bulging jaw.
No clear seasonal pattern shows up in the data, and with a comfortable range of roughly 25 to 29C it's present on these reefs year-round. Plan around good visibility and calm conditions in Sabah or Raja Ampat rather than a particular month.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
Most reliably logged in Malaysia, especially around Sabah, and across Indonesia in Maluku and Raja Ampat. It's an uncommon find rather than a guaranteed one, so expect to search coral heads and rubble patches carefully rather than spot it from a distance.
Mapping where Redspot Cardinalfish is logged…
It's most often logged in Sabah, Malaysia, and in Indonesia's Maluku and Raja Ampat regions. Search coral rubble and crevices on typical reef dives rather than expecting an open-water sighting.
There's no strong season in the sighting data, and it lives comfortably in water from about 25 to 29C, so it's around on these reefs all year.
Look for a tiny, pale, big-eyed cardinalfish around 3cm long with a small dark, red-rimmed spot near the base of the tail. It usually sits still near coral or rubble rather than swimming in open water.
They stay small, typically around 3cm as adults, making them easy to miss unless you're looking closely at coral crevices.
No, they pose no threat to divers. They're small, shelter-loving fish that simply hold their position near the reef when divers pass by.
Like many cardinalfish, males brood the fertilised eggs in their mouth until the young hatch, so a male with a visibly swollen jaw is likely guarding a clutch.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
Iridescent Cardinalfish
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