Ostorhinchus nigrofasciatus
Small striped cardinalfish tucked into reef crevices across Sulawesi, 25 to 29C year-round, uncommon but findable if you know where to look.
A small, deep-bodied fish about 7 cm long with large eyes and two dark horizontal stripes running along a pale to tan body. The stripes are the key mark, they run the length of the flank and stop short of a plain, unmarked tail, distinguishing it from busier-patterned cardinalfish. Look for it hovering nose-out from reef crevices and under ledges rather than swimming openly over the substrate.
Divers typically find it hovering in small groups just outside crevices, overhangs and reef nooks, staying close to cover rather than roaming open sand or coral flats. It holds fairly still and lets divers approach reasonably close before retreating into the reef structure, and like most cardinalfish it is most active around dusk and after dark when it disperses to feed.
Like other cardinalfish, males of this genus are mouthbrooders, carrying fertilised eggs in their mouth until the young are ready to disperse, so a male seen with a slightly swollen jaw may be guarding a brood rather than feeding.
No clear seasonal pattern shows up in the sightings, and with a comfortable water-temperature niche of 25.4 to 28.9C it's a year-round resident on the reefs where it occurs rather than a seasonal visitor.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
Most reliably logged across Sulawesi in Indonesia, with additional sightings in Raja Ampat, making Indonesia by far the strongest bet for this species. Smaller but confirmed populations turn up in Eilat in Israel's Red Sea and around Viti Levu in Fiji, with single logged sites in the Philippines' Visayas, Egypt's Red Sea Riviera, and Kwajalein Atoll in the Marshall Islands.
Mapping where Blackstriped Cardinalfish is logged…
Sulawesi in Indonesia is the strongest region, with further sightings in Raja Ampat, Eilat in Israel, Fiji's Viti Levu, the Philippine Visayas, Egypt's Red Sea Riviera and Kwajalein Atoll in the Marshall Islands.
There's no strong seasonal signal in the sightings. It sits comfortably in 25.4 to 28.9C water, so it's present on its home reefs all year round.
Look for a small, roughly 7 cm fish with two dark horizontal stripes along a pale body, large eyes, and a plain unmarked tail. It hovers near crevices and ledges rather than swimming out in the open.
They stay small, reaching around 7 cm in length, typical for reef-dwelling cardinalfish that shelter in crevices rather than open water.
No. They pose no threat to divers and simply retreat into reef cover if approached too closely.
Males are mouthbrooders, holding fertilised eggs inside their mouth until the young hatch and disperse, a trait shared across most cardinalfish species.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
Iridescent Cardinalfish
1,784 sites
