Longtail Tuna: Thailand's Light-Tackle Tuna
There is a particular kind of chaos that descends when a school of longtail tuna finds a ball of baitfish at the surface. The water goes from mirror-flat to boiling in seconds. Birds materialise from nowhere. And any lure that lands in the right place on the right cast is hit before it can complete its first action cycle. For light-tackle anglers in Thailand, this is not a daydream — it is a routine possibility on both coasts from the northeast monsoon season through to the early months of the year.
Pla o-len (ปลาโอเล็น) — the longtail tuna, Thunnus tonggol — is the most accessible of Thailand's offshore tuna species. It is smaller than yellowfin, available in greater numbers, and found in water depths that put it within reach of half-day charters and even capable shore-based anglers in the right locations. It is also, on appropriate tackle, an exceptional fighter: compact, muscular, and possessed of a bulldog determination that belies its modest maximum size.
Biology and Identification
Longtail tuna share the torpedo body plan of all true tunas but are notably more slender than yellowfin or bigeye, with a proportionally longer, more tapered caudal peduncle that gives the species its common name. The body is metallic blue-black dorsally, transitioning to silver on the flanks, with small but visible white spots on the lower flanks — a feature that helps distinguish longtail from the very similar kawakawa (Euthynnus affinis) at close range.
The pectoral fin is notably short, not extending past the first dorsal fin — an important identification point that separates longtail from yellowfin, whose pectoral fins become dramatically elongated in larger specimens. The eyes are proportionally large, reflecting the species' reliance on vision during high-speed predation.
Maximum size reaches approximately 36 kg and 145 cm, but most fish encountered in Thai recreational fishing run between 3 and 12 kg. A 15 kg fish is a noteworthy capture, and anything approaching 20 kg is genuinely exceptional in Thai waters. The IGFA all-tackle record of 35.9 kg was set in Australian waters, where the species grows to its full potential.
Longtail tuna are warm-water specialists. Unlike some tuna species that tolerate broad temperature ranges, T. tonggol is rarely found in water below 18°C, making the tropical Thai coastline near-ideal habitat for much of the year. This thermal preference also means longtail tend to stay closer to the surface than deepwater tuna species.
Distribution and Seasonality
Longtail tuna are genuinely pan-coastal in Thailand, occurring in both the Andaman Sea and Gulf of Thailand. This sets them apart from some pelagics that strongly favour one coast over the other.
On the Andaman side, longtail are present year-round in accessible numbers, with the November through April northeast monsoon window representing the peak season. The calm, clear conditions that make Andaman fishing so productive during this period also make bait balls and surface feeding activity easier to locate. The waters off Phuket, Khao Lak, and around the Similan Islands are particularly productive. The fish tend to school in shallower water — 20 to 60 metres — than the deeper-ranging yellowfin, which means they are reachable on shorter half-day trips.
In the Gulf of Thailand, longtail are a year-round presence with a peak from November through February when northeast winds and changing water temperatures concentrate baitfish. The deeper mid-Gulf waters off Koh Samui and Koh Phangan see regular longtail activity, and the eastern Gulf — particularly off the southern reaches of the Samui archipelago — is productive for anyone based in that region.
One of the longtail's most useful qualities from an angling perspective is its tendency to forage in areas where other species do not. It is found around fish aggregating devices (FADs), under floating debris, and near shallow reef edges as well as in open water, making it catchable through a wider variety of approaches than most pelagics.
Techniques
Surface Lures: The Peak Experience
When longtail tuna are actively pushing bait balls to the surface — a situation that can happen at any time of day but is most common in the first and last two hours of daylight — casting surface lures into the melee is the most effective and by some distance the most enjoyable approach.
Floating pencil poppers and walk-the-dog style stickbaits in the 100–160 mm range are the go-to tools. The key is a fast, erratic retrieve that mimics a panicked baitfish: tip down, rapid twitches, minimal pauses. Longtail in a surface blitz rarely need coaxing — they will commit to a well-presented lure within seconds. The hook is usually visual: you see the fish turn and attack before you feel anything.
Casting accuracy matters more than lure selection. Getting your lure to the edge of the bait ball — where the largest fish are working — rather than into the thick of it is more likely to produce quality fish. A cast that lands 3 to 5 metres ahead of the nearest boil and retrieves through it is the ideal scenario.
Metal slices and chrome slugs in the 40–80 g range are effective casters and produce fish when pencil poppers are refused. They work particularly well when longtail are feeding on smaller baitfish and are finicky about large surface presentations.
"Longtail don't give you time to think. The bait ball comes up fifty metres off the bow, you make the cast, and by the time you're thinking about your retrieve the line is already moving sideways. That's what I love about them." — Khao Lak light-tackle guide
Trolling and Running Lures
Many Thai charters that target Spanish mackerel and wahoo encounter longtail tuna as an incidental species in the trolling spread. Small to medium jet-heads, bibbed minnows in the 130–160 mm range, and even naked ballyhoo all attract longtail when they are in the area.
When longtail are the primary target rather than an incidental catch, dialling back trolling speed slightly — to 5–7 knots rather than the faster mackerel-targeting 8–9 knots — and running lighter leaders improves the strike rate. A 40–60 lb fluorocarbon leader rather than wire is appropriate; longtail have no significant teeth and do not require the wire protection that mackerel demand.
Vertical Jigging
Longtail that are not actively feeding at the surface can often be found in the mid-water column around FADs, current lines, and reef edges. A knife jig or slow-pitch jig in the 80–150 g range, dropped to the school depth and worked on an aggressive pitch retrieve, will produce fish that are completely invisible from the surface.
This approach pairs well with the jigging-focused charters that work the Andaman offshore seamounts — the same grounds that target dogtooth tuna and amberjack will often yield longtail as an active participant in the mixed jigging session. See our jigging Thailand deep water guide for depth charts and jig selection.
Fly Fishing
Longtail tuna are a viable fly target in Thailand, though the logistics require planning. When fish are actively schooling near the surface, a 9 or 10 weight outfit with a fast-sinking line and a baitfish pattern can produce hookups on the cast — the fish are aggressive enough and concentrated enough to make fly presentations practical. The challenge is positioning the boat at the right distance from the school without pushing fish down.
The most consistent fly-fishing scenario involves chumming with small baitfish (live or cut) to bring longtail near the boat and hold them at the surface, then presenting a fly on a slow strip retrieve. This controlled situation is easier to manage than casting to fast-moving surface blitzes and is the approach most commonly used by the handful of Andaman fly fishing specialists. For full gear recommendations, see our tropical fly fishing setup guide.
Tackle Recommendations
Light to medium spinning is the appropriate bracket for most longtail fishing. A 20–30 lb class spinning outfit gives you the casting ability to reach surface schools, the drag capacity to handle a strong run, and enough sensitivity to feel the take on subsurface presentations.
- Rod: 7–8 ft, fast action, rated 20–30 lb. A rod with enough backbone to drive treble hooks home on a long cast but with enough tip sensitivity to work walking stickbaits properly.
- Reel: 4000–5000 class spinning reel with a quality drag system capable of sustained pressure. Longtail make multiple determined runs — a drag that smooths out mid-run is essential.
- Mainline: 20–30 lb braid. The thin diameter gives casting distance; the low stretch translates hooksets across long casts.
- Leader: 30–50 lb fluorocarbon, 60–90 cm. Longtail have no teeth to worry about, so leader strength is primarily about abrasion on the body of the fish during a long fight.
For charter trolling situations where longtail are an expected incidental species, the existing medium-heavy conventional gear used for mackerel and wahoo handles longtail comfortably.
Finding Fish: Practical Tips
The classic longtail indicator is birds. Frigate birds and terns that are actively diving — not just gliding — mean something is pushing bait to the surface below them, and longtail are one of the most common culprits in Thai waters. Learning to read bird activity at distance is the single most useful skill for finding surface-feeding tuna.
Beyond birds, look for:
- Temperature breaks: The transition zones between water masses of different temperatures concentrate baitfish and the tuna that follow them. A good fish finder showing temperature change at the thermocline is worth its cost in the first day.
- Current lines: Floating debris, foam lines, and current edges that collect small organisms attract baitfish, which attract tuna.
- FADs: Fish aggregating devices — floating objects deployed deliberately or drifting naturally — concentrate longtail reliably. Many Thai charter captains know the locations of working FADs on their regular grounds.
- Reef edges: Longtail feed along reef drop-offs, particularly at dawn and dusk. The Andaman reef systems between Phuket and the Similans offer productive edge fishing with appropriate sounder work.
For the full seasonal picture on both coasts, see the Andaman Sea fishing guide and the Gulf of Thailand fishing guide.
Conservation
Longtail tuna are categorised as Least Concern on the IUCN Red List, with populations considered stable across most of their range including Thai waters. They are faster-growing and more fecund than larger tuna species, which gives them greater resilience to fishing pressure. Commercial harvest in Thailand is significant — longtail appear frequently in fresh markets on both coasts — but recreational impact is modest relative to the population size.
The main conservation consideration is responsible handling. Longtail destined for release should be brought to the boat quickly on appropriate tackle — a prolonged fight on light gear is harder on the fish than a shorter fight on heavier tackle. Keep the fish in the water when removing hooks, support the body, and allow a full recovery before release.
