Bigeye Trevally

The bigeye trevally (Caranx sexfasciatus), also known as the bigeye jack, great trevally, six-banded trevally, and dusky jack, is a prominent marine species within the family Carangidae. It is notably distributed across the tropical waters of the 🇮🇳 Indian and 🌊 Pacific Oceans, extending from the western regions of 🇿🇦 South Africa to the eastern reaches of California and 🇪🇨 Ecuador, and spanning from 🇦🇺 Australia in the south to 🇯🇵 Japan in the north. This species can be identified by its distinctive coloration, which includes a dark second dorsal fin featuring a white-tipped lobe and a small dark spot on the operculum. The bigeye trevally can grow to a considerable size, reaching lengths of 120 cm and weights of up to 18 kg.

The bigeye trevally primarily inhabits inshore environments, occupying reef areas down to depths of approximately 100 meters, and frequently venturing into estuaries and sandy bays during its juvenile phase. Typically organized in large, slow-moving schools during daylight hours, it becomes active at night. Its diet consists of various fish, crustaceans, cephalopods, and other invertebrates, with a dietary shift from crustaceans in its juvenile stage to predominantly fish as an adult. Sexual maturity is achieved at a length of 42 cm, with spawning occurring in large aggregations typically from July to March across its range. The species holds moderate economic importance to fisheries; it is particularly significant to certain artisanal fisheries, utilizing methods such as gill nets, purse seines, and hook and line fishing. It is regarded as fair to good for consumption, and is also valued as a gamefish, attracting anglers using lures, bait, and spears.

Taxonomically, the bigeye trevally belongs to the genus Caranx, within the jack and horse mackerel family Carangidae, itself a subset of the order Carangiformes. Recognized commonly as the 'bigeye trevally' or 'bigeye jack,' this species is occasionally referred to by alternative names such as 'great trevally' or 'dusky jack.'

One of the larger members of the Caranx genus, the bigeye trevally possesses a compressed, oblong body with a more convex dorsal profile compared to the ventral side. Its anatomical features include a pointed snout, a two-part dorsal fin with a unique configuration of spines and soft rays, a strongly forked caudal fin, and distinct dentition comprising both canine and conical teeth. Notably, the species undergoes notable color transformations as it matures: juveniles exhibit silvery yellow to brown hues with prominent vertical bands, which fade as they age, resulting in a silvery olive to blue-green dorsal coloration in adulthood.

The geographical range of the bigeye trevally is extensive, encompassing the 🌊 Indian Ocean from 🇿🇦 South Africa to 🇲🇬 Madagascar, through to Southeast Asia, and as far north as 🇯🇵 Japan and south to 🇦🇺 Australia. In the 🌊 Pacific Ocean, its distribution includes numerous tropical island groups, extending eastward to the American coastline.

Predominantly inhabiting coastal inshore waters, the bigeye trevally also frequents offshore pelagic zones, often around remote islands and seamounts. It is primarily associated with coral and rocky reef ecosystems in adulthood but can be found in sandy bays and lagoons. Juveniles reside in shallower estuarine and mangrove zones, even venturing into riverine environments.

Exhibiting schooling behavior, the bigeye trevally forms aggregations exceeding 1500 individuals, especially around reef structures. While predominantly a nocturnal predator, its feeding activities shift at dusk, focusing largely on small fish supplemented by diverse invertebrates. Studies indicate dietary variations based on size, with juveniles consuming more penaeid shrimps alongside fish. The species also serves as prey for larger marine predators, contributing to its ecological significance.

In conclusion, the bigeye trevally represents an ecologically and economically valuable species within its expansive range, characterized by its distinct morphology, extensive habitat utilization, and dynamic feeding behavior.