Turrum coeruleopinnatum
Small, quick jack seen year-round in 24-29C water off Longdong, Taiwan. Here's how to spot one and what to expect.
A compact jack that tops out around 29cm, with the streamlined, laterally compressed body typical of the trevally family. Look for a blue-tinted back and fins that give it its name, fading to a paler silver flank and belly. The tail is deeply forked and the profile is slim and fast-looking, built for short bursts rather than cruising.
Divers log this one as uncommon, so sightings tend to be brief, a lone fish or small group cutting past over rock or reef rather than lingering for a photo. Like other small jacks it likely patrols mid-water or hugs structure while hunting, staying alert to divers and keeping some distance rather than approaching.
It's one of the lesser-known members of the jack family, with so few confirmed dive logs that Longdong, Taiwan is currently the only well-documented place to look for it underwater.
There isn't enough data yet to point to a season, and water temperatures at the sites where it's seen range from 24.4 to 28.9C, comfortable most of the year. Treat it as a year-round possibility at Longdong rather than a seasonal target.
Reef neighbours a diver could mistake it for. Use the identification notes above to tell them apart.
Every logged sighting so far comes from Taiwan, and specifically Longdong on the island's northeast coast, which is currently the only known reliable spot for this species. If you're diving Longdong, keep an eye on rocky reef edges and current-swept points where smaller jacks tend to hold station.
Mapping where Bluefin Kingfish is logged…
The only well-documented sightings come from Longdong on Taiwan's northeast coast. It's currently the single reliable region for this species in diver records.
There's no clear season in the data. Water at the sites where it's seen stays between 24.4 and 28.9C, so it's a year-round possibility rather than a seasonal event.
Look for a small jack, under 30cm, with a blue-tinted back and fins, a silvery compressed body, and a deeply forked tail. It's built for quick bursts of speed, not slow cruising.
They're a small jack, typically around 29cm, noticeably smaller than the bigger trevallies divers often see them confused with.
No. They're a small, fast-moving jack with no history of aggression or risk to divers.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
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