Bigeye Trevally

Bigeye Trevally

The bigeye trevally (Caranx sexfasciatus), also known as the bigeye jack, great trevally, or six-banded trevally, is a large marine fish belonging to the jack family, Carangidae. It is easily distinguished from other members of its genus by its prominent eyes featuring well-developed adipose eyelids, a small dark spot on the operculum, and a dark second dorsal fin featuring a distinctive white tip. Adult colouration ranges from dark bluish-green to gold along the dorsal side, fading into a paler yellowish-green or silvery tone beneath. The caudal fin is dark, while the soft dorsal and anal fins display dusky tips. Juvenile bigeye trevallies exhibit four to seven broad dark vertical bars across their flanks and a yellowish caudal fin with a black upper tip. As adults mature, they can reach lengths up to 120 centimetres and weigh as much as 18 kilograms, though individuals around 60 centimetres are more frequently encountered on dive sites. Their streamlined, compressed bodies allow them to move efficiently through open water with remarkable speed and agility. During daylight hours, bigeye trevallies gather in massive, slow-moving schools over coral and rocky reef complexes. These dense aggregations serve primarily as a defensive mechanism against larger marine predators such as sharks. As dusk approaches, the daytime schools disperse, and individual fish or smaller hunting packs become active, ranging across the reef and adjacent open waters to feed under the cover of low light. The Bigeye Trevally, Caranx sexfasciatus, typically exhibits schooling behaviour, forming large aggregations during both day and night, though their activity often peaks at dusk and dawn when they actively forage. These schools, sometimes comprising thousands of individuals, are often observed in coastal waters, reefs, and estuaries. Reproduction in this species is via broadcast spawning, where eggs and sperm are released into the water column for external fertilisation. While specific spawning periods can vary geographically, it is generally documented as occurring during warmer months, often associated with specific lunar cycles. Females release numerous pelagic eggs, a characteristic of broadcast spawners, though precise clutch sizes are highly variable and not consistently quantified. After a short incubation period, larvae hatch and undergo a pelagic developmental stage, eventually settling into more sheltered nursery habitats such as mangroves and estuaries before maturing into adults, a process that typically takes a few years. The species is broadly distributed across the tropical and subtropical waters of the Indian and Pacific Oceans. Its range stretches from South Africa, Madagascar, the Red Sea, and the Persian Gulf across India, South East Asia, and Australia, extending north to Japan and east across Pacific island groups to Hawaii, California, Ecuador, and the Galápagos Islands. For scuba divers, encountering a dense, shimmering tornado of bigeye trevallies as they navigate reef edges or drop-offs remains one of the most iconic spectacles in tropical marine diving.