Barracuda Tornado, Koh Tachai, Similan Islands February 2025

Hundreds of barracuda circling over Koh Tachai pinnacle on a Similan Islands liveaboard trip – an absolutely epic encounter

Barracuda Tornado, Koh Tachai, Similan Islands, Thailand, February 2025 © chris@divehappy.com

This is one of those “is this really happening?” moments while diving. You’re bobbing around at 10 metres over Koh Tachai pinnacle and then something starts to emerge from the blue gloom at the edges of your vision.

Barracuda Tornado, Koh Tachai, Similan Islands, Thailand, February 2025 © chris@divehappy.com

Shifting fast in perfect unison, hundreds of barracuda circling each other in a formation that’s three stories high and rapidly moving towards the pinnacle – and you. Once they arrive at the top of the pinnacle, they continue to circle, as if anchored to the same spot. The entire school moves as a single organism. The formation expands and contract like it was breathing, with individual fish disappearing into the mass and reappearing elsewhere.

Barracuda Tornado, Koh Tachai, Similan Islands, Thailand, February 2025 © chris@divehappy.com

The movement, the synchronicity, the size, the light reflecting off the barracuda’s silver skin – it is just awe-inspiring to see it happen right in front of you. The perfect circle of the cyclone holds for a few seconds and then it disperses as the barracuda break up, shift in different directions and then come back together to reform once again.

Barracuda Tornado, Koh Tachai, Similan Islands, Thailand, February 2025 © chris@divehappy.com

Why do barracuda behave like this? Supposedly, when barracuda sense danger – usually from larger predators like sharks or tuna – they abandon their usual lone-wolf hunting style and band together in these tight, rotating formations.

Barracuda Tornado, Koh Tachai, Similan Islands, Thailand, February 2025 © chris@divehappy.com

Each fish is essentially trying to get to the safest spot, which is the centre of the group. But since every fish has the same idea, they create this constant spiral motion as they jostle for position. The result looks like an underwater tornado made entirely of fish.

Pook in the Barracuda Tornado, Koh Tachai, Similan Islands, Thailand, February 2025 © chris@divehappy.com

For any predator trying to pick off a meal, it becomes an impossible task. Imagine trying to catch one specific fish from a swirling mass of hundreds, all flashing silver and moving in perfect coordination. The visual chaos is so overwhelming that even the most skilled hunters often give up and look elsewhere.

Pook in the Barracuda Tornado, Koh Tachai, Similan Islands, Thailand, February 2025 © chris@divehappy.com

The Similan Islands seem to be one of the few places where conditions align perfectly for this behavior. The granite pinnacles and seamounts create upwelling currents that bring nutrients and smaller prey fish to the area. This abundance attracts both the barracuda and the larger predators that hunt them

Pook in the Barracuda Tornado, Koh Tachai, Similan Islands, Thailand, February 2025 © chris@divehappy.com

I’d seen this once before at the Similans’ Three Trees dive site back in December 2024, but honestly wasn’t sure I’d ever encounter it again – definitely not a couple of months later. (See the barracuda tornado at Three Trees photos).

Pook in the Barracuda Tornado, Koh Tachai, Similan Islands, Thailand, February 2025 © chris@divehappy.com

The Blue Dolphin liveaboard‘s dive guides mentioned that the barracuda tornadoes are seen a few times each season, usually towards the end of the season in April and May.

Barracuda Tornado Approaching

Barracuda Tornado in the distance, Koh Tachai, Similan Islands, Thailand, February 2025 © chris@divehappy.com

The three photos below show the tornado forming and approaching the pinnacle in the distance. You can tell this is further away as there’s less light on the barracuda themselves.

Barracuda Tornado in the distance, Koh Tachai, Similan Islands, Thailand, February 2025 © chris@divehappy.com

As the barracuda get nearer, constantly circling in formation and gliding towards me simultaneously, you can see the tornado form.

Barracuda Tornado, Koh Tachai, Similan Islands, Thailand, February 2025 © chris@divehappy.com

By this point they’re so near I can’t fit them all into the frame. It is quite a humbling experience to watch this army of barracuda approach and be engulfed by it.

Barracuda Tornado Dispersing

Barracuda Tornado, Koh Tachai, Similan Islands, Thailand, February 2025 © chris@divehappy.com

The rest of the photos below show the barracuda as they break formation and move in a huge wall passing across the top of Koh Tachai pinnacle. They’re not quite in circular formation anymore, more just marauding, before they finally exit back out into the blue as if nothing had ever happened. All told, the barracuda were with us for about 10 minutes I think.

Barracuda Tornado, Koh Tachai, Similan Islands, Thailand, February 2025 © chris@divehappy.com

Recommended Similan Liveaboards October 2025 to May 2026

This was all part of an epic Similan liveaboard trip in February 2025 where we had an amazing run of luck – not just the barracuda tornado but also a jack tornado at Richelieu Rock and a manta ray at Koh Bon, among all sorts of other stuff. See the full trip report.