Coastal Trevally

The coastal trevally, scientifically known as Carangoides coeruleopinnatus and commonly referred to as the onion trevally, 🇯🇵 Japanese trevally, or bluefin kingfish, is a marine species belonging to the jack family, Carangidae. This species is distributed throughout the tropical and subtropical regions of the 🇮🇳 Indian and western 🌊 Pacific Oceans, ranging from 🇿🇦 South Africa to 🇯🇵 Japan and 🇳🇨 New Caledonia (🇫🇷 Overseas France), and extending as far south as 🇦🇺 Australia. Typically found on deep coastal reefs, the coastal trevally can be observed both in solitary and in groups, feeding on small midwater organisms such as crustaceans, small fish, and cephalopods. Although often caught as bycatch in various fisheries within its habitat range, it holds minimal commercial value. Nonetheless, it is highly regarded as a quality table fish. A typographical error in the original classification by Eduard Rüppell introduced the variant Carangoides caeruleopinnatus, which has been inaccurately perpetuated in some scientific literature.

The species belongs to the genus Carangoides, within the family Carangidae, further classified under the order Carangiformes—a group that includes several species commonly referred to as jacks and trevallies. It is predominantly recognized by names such as 'coastal trevally' or 'coastal kingfish', along with 'onion trevally', '🇯🇵 Japanese trevally', 'bluefin kingfish', 'shortfin kingfish', and 'diverse trevally' among English-speaking communities.

The coastal trevally exhibits morphological characteristics similar to other jack species, including a nearly ovate, strongly compressed body with a dorsal profile that is more convex than the ventral profile and a moderately curved nape. The species can grow up to a maximum size of 40 cm, though it is more commonly encountered at approximately 25 cm in length. In appearance, the coastal trevally displays a bluish-green coloration dorsally, transitioning to a silvery grey on the ventral side. The body is adorned with numerous small yellow spots, complemented by a distinct dark blotch on the upper margin of the opercle. The dorsal, anal, and caudal fins are typically dusky, with the latter occasionally exhibiting a yellowish hue, whereas the pectoral fins are pale yellow, and the pelvic fins range from hyaline to grey. Juveniles display dark vertical bands that fade with maturity and become indistinct as they grow larger.

Geographically, the coastal trevally is broadly distributed across the tropical and subtropical waters of the 🇮🇳 Indian and western 🌊 Pacific Oceans. Its western boundary extends along the east coast of Africa, from 🇿🇦 South Africa and 🇲🇬 Madagascar northward to the 🌊 Red Sea and the 🌊 Persian Gulf. Its habitat encompasses the coastal regions of 🇮🇳 India, including 🇱🇰 Sri Lanka, and extends across the Asian coastline to territories such as 🇨🇳 China and 🇹🇭 Thailand, spanning the Southeast Asian and 🇮🇩 Indonesian archipelagos to northern 🇦🇺 Australia. In the Pacific, its range reaches north to 🇹🇼 Taiwan and 🇯🇵 Japan, and eastward to various island groups including 🇹🇴 Tonga, 🇼🇸 Samoa, and 🇳🇨 New Caledonia (🇫🇷 Overseas France). While coastal trevally are seldom encountered nearshore, adult specimens are predominantly associated with deep coastal reef ecosystems and are hypothesized to display a pelagic lifestyle. Juveniles have been observed in Natal estuaries and shallow bays in northern 🇦🇺 Australia, though details regarding their movement patterns remain insufficiently understood. Similar to other jack species, the coastal trevally is known to aggregate around fish attracting devices (FADs), where it is occasionally captured by recreational anglers.

The biology and ecology of the coastal trevally remain inadequately studied, leading to limited information in these domains. The species is known to exist in small shoals or individually, and its feeding habits classify it as planktonivorous, primarily consuming small midwater organisms including krill, mantis shrimp, small fish, and squid. The coastal trevally's soft mouth and weak teeth constrain its ability to capture larger prey, contributing to its relatively sluggish demeanor compared to other Carangidae members. Knowledge regarding the reproductive behavior and migration patterns of this species remains lacking.

From a fisheries perspective, the coastal trevally holds limited significance across its distribution, mainly encountered as bycatch in finfish and prawn fishing operations utilizing techniques such as hook and line, gill nets, and various traps. Due to its affinity for deep reef habitats, the species is of minor interest to sport anglers and is infrequently targeted by them. Despite its marginal commercial value, particularly in Asia, the coastal trevally is esteemed as a beneficial fish for culinary use.