The Diamond Trevally is a large species of coastal marine fish of the jack family, Carangidae. The Diamond Trevally has the typical body structure of a large jack, with a distinctly angular, strongly compressed body. The Diamond Trevally is one of three members of the diamond trevally genus Alectis, which itself is one of 33 genera encapsulated in the jack family, Carangidae. The Carangidae are perciform fishes in the suborder Percoidei. It is a large species, growing to 165 cm and 25 kg in weight. The species is carnivorous, consuming fishes, cephalopods and crustaceans. The Indian threadfin is of minor commercial importance, and has been the subject of aquaculture in Singapore.
The major identifying feature of the species is its head profile, having a slight concavity near the eyes which distinguishes it from its close relatives in the genus Alectis. The dorsal profile of the fish is more curved than the ventral profile, and the body is deepest between the origins of the soft dorsal and soft anal fins. The first section of the dorsal fin consists of 5 to 7 visible spines, with the second section having one spine and 18 or 19 soft rays. The anal fin has two spines followed by a single spine and 15 or 16 soft rays. The pectoral fin is long and curved, extending beyond the junction of the straight and curved sections of the lateral line. The body appears to be scaleless, but on closer inspection has minute, deeply embedded scales. The lateral line is strongly curved anteriorly, with a section of 6 to 11 scutes toward the tail. Juveniles have long, filamentous trailing anal and dorsal fin spines, much like those of Alectis ciliaris. The species is known to grow to 165 cm and 25 kg.
Diamond Trevally like a crustacean - imitative shrimp, prawn and crab patterns especially. They like to feed around rays. They are commonly caught with cut baits intended for other species, If you’re fly fishing they can sometimes be difficult to hook on conventional streamer flies, but they will take imitative shrimp, prawn and crab patterns especially when they are hunting and feeding in close association with rays. When hooked, they have a blistering initial burst of speed and will usually make a bee-line for deeper waters before arcing and plugging.
The Diamond Trevally inhabits the tropical regions of the Indian and Western Pacific Oceans, ranging from Madagascar, east Africa and the Red Sea to India, China, South East Asia, north to Japan and south to Indonesia and northern Australia. The eastern most report is that of a specimen taken off French Polynesia in the Pacific.
The species is generally an inhabitant of coastal waters from depths of 20 m to 100 m, although the juveniles may be pelagic, riding ocean currents. In some years currents bring the juveniles as far south as Sydney, Australia where they inhabit of estuaries in the summer, before dying off in the cold winter. The African pompano shows a similar pattern in Australian waters. The juveniles are also known to inhabit estuaries in other regions (including South Africa) as well as seagrass beds. Adults generally inhabit areas of reef below 20 m.
In Australia the Diamond Trevally is known from south-western Western Australia, around the tropical north of the country and south to the central coast of New South Wales.