Cephalopholis formosa
Small reef grouper with electric-blue stripes, logged widely off Phuket and Malaysia's East Coast in warm 27-29C water year-round.
Small, slender grouper reaching about 23 cm, with a reddish-brown to olive body covered in narrow, wavy blue lines running along its length. It sits low on the reef near ledges and holes rather than swimming in open water, and the blue striping is the giveaway mark that separates it from plainer small groupers at a glance.
Usually spotted tucked close to reef structure, hovering near crevices, overhangs or coral rubble rather than out in the open. It tends to hold its ground or duck just out of sight when divers approach, and most logs describe single fish rather than groups, so it's a spot-and-move-on sighting rather than something to linger with.
Like other hinds and groupers in this family, it's a protogynous hermaphrodite, meaning individuals start life as females and some later change into males as they grow.
No clear seasonal pattern shows up in the data, and with water sitting a steady 26.5 to 29.3C across its range, it's a year-round resident of these reefs 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 along Peninsular Malaysia's East Coast and across Sabah, with Phuket, Koh Phi Phi, Koh Tao and Koh Chang in Thailand all producing regular sightings. It also turns up around Sihanoukville in Cambodia and on reefs in India, making it a widespread but always low-key find across Southeast Asian reef diving.
Mapping where Bluelined Hind is logged…
It's most consistently found on reefs along Peninsular Malaysia's East Coast and in Sabah, plus popular Thai sites like Phuket, Koh Phi Phi and Koh Tao. Sihanoukville in Cambodia and reef sites in India also produce regular sightings.
There's no strong seasonal pattern in sightings, and it lives in consistently warm water year-round, so it's a fair bet on any dive in its range regardless of month.
Look for a small, slender grouper around 23 cm long with a reddish-brown body marked by thin, wavy blue lines. It's usually tucked near reef ledges or crevices rather than out swimming, which helps narrow it down from similar small groupers.
They're a small reef grouper, typically reaching around 23 cm, so don't expect the bulk of larger grouper species. Most divers spot them at or near this adult size.
No, they're not considered a risk to divers. They're small, reef-associated fish that tend to retreat toward cover rather than approach, so no special caution is needed.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
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