Bluefin trevally

What it is

This large marine fish belongs to the jack family. It has an oblong, compressed body with a pointed snout. Adults display electric blue dorsal, anal, and tail fins. Their sides feature numerous blue-black spots that increase with age. The upper body is silver-brassy, fading to white below. Juveniles lack these bright colours and have dark fins. They grow to a maximum length of 117 cm and weigh up to 43.5 kg, though most caught are smaller than 80 cm.

Where it lives

The species inhabits tropical and subtropical waters across the Indian and Pacific Oceans. Its range extends from South Africa and the Red Sea east to Central America. It is common around Indonesia, Australia, Japan, and Hawaii. In the eastern Pacific, it reaches the Galápagos Islands. The fish lives in diverse marine settings, including bays, lagoons, and coral reefs. Juveniles prefer shallow, protected waters, while adults occupy deeper offshore slopes and atolls up to 183 metres deep.

How it lives

Juveniles school together, but adults become solitary with defined home ranges. They hunt using aggressive midwater attacks and reef ambushes. Their diet consists mainly of fish, supplemented by squid and crustaceans. They sometimes follow larger predators to catch missed prey. Tracking studies show they patrol reef walls during the day. At night, they congregate in specific areas before returning to their daytime ranges. Some individuals rub against sharks to remove parasites, a rare cleaning behaviour.

Breeding and life cycle

Spawning occurs at different times depending on the location. Fish reach sexual maturity at two years of age, when they are 30 to 40 cm long. They are multiple spawners, capable of reproducing up to eight times annually. A single female can release millions of eggs per year in captivity. Growth is rapid, with juveniles reaching nearly 20 cm in their first year. This fast growth and high fecundity support research into farming the species.

Fish and people

Fishermen value this species for both commercial and sport purposes. Catches in the western Indian Ocean reach 50 tonnes yearly. In Hawaii, it is the most common trevally taken in tournaments. Overfishing has reduced populations in inhabited Hawaiian islands. Consequently, scientists study its aquaculture potential, achieving spawning in captivity. While popular as food, eating large specimens carries a risk of ciguatera poisoning, a type of foodborne illness caused by toxins in reef fish.

Questions people ask about Bluefin trevally

Good reading and sources

• Bluefin trevally on WikipediaEncyclopedia
• More photos on Wikimedia CommonsPhotos
• Wikidata recordOpen data