Thailand is a fishing country split down the middle by geography. On one side is the Andaman Sea — deeper, more volatile, seasonally shut, and home to the nation's most dramatic sportfishing. On the other is the Gulf of Thailand — shallower, more accessible across more months, and producing a different class of fish. Most anglers who plan a Thai fishing trip treat the coasts as interchangeable. They are not. This is the guide that explains why, and which one you should target.
The Andaman: Big Fish, Tight Window
The Andaman Sea is generated by the Indian Ocean, and it shows. The water deepens quickly off the Thai coast, seamounts rise from 400 metres, and the current systems that sweep through the Malacca Strait push baitfish and predators into predictable aggregations. This is where Thailand's sailfish live in serious numbers, where blue and black marlin are genuinely targetable, and where giant trevally grow to sizes that break tackle.
The operational season runs November through April. Early November brings the first settled weather after the southwest monsoon. By December the sea is flat and clear. January through March is the core peak — sailfish are thick off Phuket, Khao Lak, and Koh Rok, which holds some of the most concentrated sailfish fishing in Southeast Asia during this window. April marks the start of the wind building again, and by May most offshore operators have pulled their boats. The full seasonal picture is in the Andaman Sea fishing guide.
January through March on the Andaman is one of the best windows for billfish in all of Southeast Asia. The fish are there, the sea is flat, and the infrastructure exists to access them properly.
The inshore fishery is equally compelling. Giant trevally hunting on surface poppers at the rock pinnacles near Racha Yai and Racha Noi is among the most exhilarating fishing Thailand produces — pure violence when a 15 kg GT rolls on a popper at close range. Deeper jigging around the Similan Islands targets ruby snapper, grouper, dogtooth tuna, and amberjack. There is also a meaningful jigging scene in deeper Andaman water — covered in the deep-water jigging guide for Thailand.
The constraint is real: if you arrive outside November–April, the Andaman is not available for offshore fishing. This is not a soft advisory. Seas of 3–4 metres are common during the southwest monsoon and the charter fleet stops. Plan accordingly.
The Gulf of Thailand: Access Over Drama
The Gulf of Thailand is a semi-enclosed body of water roughly 800 kilometres long and rarely deeper than 80 metres. Its fish are shaped by that geography — primarily reef-associated species and mid-range pelagics rather than deep-water giants. What it offers in return is access across a far longer calendar window.
The Gulf's northeast coast (Koh Samui, Koh Tao, Koh Phangan) fishes well from March through September, with a rough northeast monsoon interruption from October into December. The western Gulf around Hua Hin and the upper reaches toward Bangkok's offshore zone is calmer and fishes through more of the year. Pattaya, on the eastern Gulf coast, has a compact but functional charter fleet and can be fished in most months. Full details on the Gulf of Thailand fishing guide.
The Gulf and Andaman seasons partially overlap in March and April — a narrow but useful window if you want to hit both coasts on one trip. Allow at least four days per coast to make it worthwhile.
The headline targets are king mackerel, queenfish, barracuda, trevally, and barramundi near the estuaries and mangrove systems. Yellowfin tuna show up further offshore in the Gulf, though a 30 kg fish is a big one compared to the Andaman's larger specimens. Squid jigging is popular and productive, particularly at night around the commercial squid-boat lights. What the Gulf lacks is the trophy tier — there is no billfish scene to speak of, no dogtooth tuna in numbers, and GT popping on surface gear is not a developed product.
Reading the Calendar
The interplay between the two monsoons creates Thailand's fishing calendar. The southwest monsoon (May–October) closes the Andaman and opens the Gulf. The northeast monsoon (October–December) roughens the Gulf's east coast and eases as the Andaman reopens. The transitional months — November and March to April — are when both coasts can be productive, which is useful for multi-destination trips.
For anglers planning their trip around the fishing rather than around other commitments:
- November–February: Andaman only. Go to Phuket, Khao Lak, or Krabi.
- March–April: Both coasts viable. Andaman still good; Gulf switching on.
- May–September: Gulf only. Koh Samui, Pattaya, or Hua Hin.
- October: Transition month. Gulf east coast rough; plan carefully.
Infrastructure: An Honest Gap
The Andaman's charter infrastructure is significantly more developed. Phuket alone has 50+ operators running boats from half-day longtail trips to full offshore sportfisher charters. The Phuket charter operators overview lists the serious players. Khao Lak has its own fleet with a different character — see Khao Lak charter operators. The guides are experienced, the boats are maintained for offshore conditions, and there is genuine competition on price and service.
The Gulf's charter infrastructure is more variable. Koh Samui has fewer than ten serious fishing operators. Pattaya has a modest but functional fleet aimed partly at expat anglers based in Bangkok. Hua Hin is thinner still. This does not mean the fishing is bad — it means you need to research operators more carefully and book further in advance during peak season. See Koh Samui charter operators for the current Samui situation.
Verdict
The Andaman Sea is Thailand's superior sportfishing coast by almost every metric that a serious angler cares about: bigger fish, more species diversity, better-developed infrastructure, and access to world-class billfish grounds. If fishing is the primary purpose of your trip and your travel window fits the November–April season, the Andaman is the correct choice. The sailfish season guide and the GT popping guide for the Andaman give you everything you need to plan specifically.
The Gulf of Thailand wins on calendar flexibility and accessibility for the non-peak traveller. If you are arriving between May and September, if you are combining fishing with other activities, or if you simply want to fish Thai waters across a broader range of months, the Gulf delivers. The fish are smaller, but the experience is still genuinely good — and on the Gulf, you can fish when the Andaman is firmly closed. Both coasts belong in a serious Thai fishing itinerary over time. For a single trip, know your window and commit to the coast that fits it.
