Bigeye Trevally

The Bigeye Trevally is a large, robust jack (family Carangidae) widespread throughout the Indo-Pacific, from East Africa and the Red Sea to Hawaii and the eastern Pacific. Renowned among divers for forming spectacular, tightly packed schools - sometimes numbering in the thousands - that swirl in tornado-like formations around reef drop-offs and passes, it is one of the most recognizable large reef predators in the region. Adults tend to darken with age, developing a near-black coloration, while juveniles remain silvery. It supports recreational and commercial interest across its range but faces no major conservation concern overall, remaining common and widely distributed on healthy Indo-Pacific reef systems.

• Deep, oval, laterally compressed body typical of large Caranx jacks
• Silvery body darkening to bronze or near-black in large adults
• Faint dusky bars sometimes visible on the flanks (source of the specific name sexfasciatus, "six-banded")
• Large eye with a well-developed adipose eyelid
• Black tip on the second dorsal fin lobe
• Strongly forked tail

Reaches 35-60 cm commonly, up to 85 cm. The combination of a black-tipped dorsal fin, dark adult coloration, and schooling behavior around reef passes separates it from the similarly shaped but paler Giant Trevally.

Bigeye Trevally occupy coral reefs, lagoons, and adjacent open water throughout the Indo-Pacific, from the Red Sea and East Africa across to Hawaii and the eastern Pacific. They are commonly encountered around reef drop-offs, channels, and passes where currents concentrate prey, typically at depths from the surface to about 60 m. Juveniles often inhabit shallow, sheltered inshore areas, estuaries, and even brackish river mouths before moving to deeper reef habitats as they mature. Adults frequently gather in large daytime schools near structure, dispersing at night to hunt individually, making time of day an important factor in observing their characteristic schooling behavior.

Bigeye Trevally are highly social during the day, forming dense, swirling schools around reef passes and drop-offs, a behavior thought to reduce predation risk and may relate to social spawning aggregations. At night, schools disperse and individuals become solitary, active nocturnal hunters, using their large eyes to locate small fish and crustaceans in low light. They are opportunistic carnivores, preying on smaller reef fish, shrimp, and cephalopods. Spawning aggregations can form seasonally at specific reef sites, particularly around new and full moons. As abundant mid-to-upper level predators, they play a significant ecological role in structuring reef fish communities across their Indo-Pacific range.