Cobia Fish
Scientific name Rachycentron canadum
The Cobia is a powerful, fast-swimming pelagic fish that occasionally cruises through Koh Tao’s dive sites. Growing up to 2 meters in length, they have a long, torpedo-shaped body, broad flattened head and a distinctive dark horizontal stripe running from nose to tail.
At first glance, they can resemble a small shark due to their shape and confident movement through the water. But look closer and you’ll see their large pectoral fins and smooth, scale-covered body give them away. They often swim alone or in small groups and are known for their curious nature around divers.
Around Koh Tao, Cobia are usually seen at deeper pinnacles and offshore sites, passing through the blue rather than sticking close to the reef. They sometimes follow larger animals such as whale sharks, turtles or even rays taking advantage of disturbed prey. When one appears mid-water, it often glides calmly past before disappearing back into the blue.
Cobia are apex mid-water predators, feeding on fish, squid and crustaceans. Their presence indicates healthy offshore ecosystems with strong food chains. While not a daily sighting, encountering a Cobia adds a sense of open-ocean energy to the dive.
They are completely harmless to divers. Despite their size and strength, they show no aggression toward humans and are sometimes surprisingly inquisitive.
A Cobia sighting feels like a glimpse of the wider ocean beyond the reef — fast, sleek and untamed.
Find Cobia Fish at...
Divemaster's tip
Keep your eyes in the blue when diving offshore pinnacles. Cobia often appear slightly deeper than the reef line or cruising along current edges. They may approach divers briefly out of curiosity before continuing on their route.
Stay mid-water aware — especially during safety stops — as pelagic visitors often pass through when least expected.
What do they eat?
Cobia feed primarily on fish, squid, crabs and other crustaceans. They are opportunistic hunters and sometimes trail larger marine animals to ambush prey stirred up from the reef or seabed.
Their speed and strength make them efficient predators in open water, and their streamlined shape allows them to cover large distances in search of food.
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