Ferdauia orthogrammus
Silvery reef jacks logged around Alofi, Niue in warm 24-29C water, usually seen alone or in small uncommon groups over the reef edge.
Streamlined, laterally compressed body typical of a jack, growing to around 52 cm, with silvery-grey flanks that flash pale gold or bronze in open water. The head profile is steep and slightly blunt, and the tail is deeply forked with a faint dark edge. Look for a single row of small scutes (hardened scales) running along the rear portion of the lateral line, a detail that separates it from smoother-bodied lookalikes at a glance.
Divers generally find it cruising alone or in loose small numbers along reef edges and drop-offs rather than schooling tightly like some of its relatives. It tends to keep a bit of distance from divers, moving steadily through open water rather than holding station, and sightings are logged as uncommon rather than a guaranteed encounter.
Like other jacks, it hunts by outrunning prey in open water rather than ambushing from cover, which is why you're more likely to see it mid-water off a reef edge than tucked into a coral crevice.
Recorded across a temperature range of roughly 23.7 to 29 C with no detected seasonal pattern, so treat it as a year-round possibility on Niue's reefs rather than a seasonal target.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
Most consistently logged around Alofi in Niue, where it turns up at the majority of the sites reporting this species. A single confirmed sighting also comes from New South Wales, Australia, so while it has a wider Pacific range, Niue is currently the reliable place to look for it.
Mapping where Island Trevally is logged…
The most reliable region is Alofi in Niue, where it has been logged at several dive sites. There is also a single record from New South Wales, Australia, but Niue is the stronger bet.
There's no clear seasonal pattern in the sightings data, and it's been recorded across a wide 23.7 to 29 C range, so it's best treated as a year-round sighting on Niue's reefs.
Look for a silvery, laterally flattened jack around 52 cm long, with a steep head profile and a deeply forked tail. A row of small scutes along the rear lateral line is a useful confirming detail.
They typically reach around 52 cm, a mid-sized jack that's noticeably smaller than a Giant Trevally but similar in build to a Bluefin Trevally.
No, they're not considered dangerous to divers. They tend to keep their distance rather than approach, and there's no recorded aggressive behaviour toward divers.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
Rainbow Runners
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