Blue Trevally

The blue trevally (Carangoides ferdau), also known by several other names such as the banded trevally, barred trevally, Ferdau's trevally, and Forskaal's jackfish, is a prevalent species of pelagic marine fish belonging to the jack family, Carangidae. This species is distributed across the tropical and subtropical waters of the Indo-Pacific and central Pacific regions, extending from 🇿🇦 South Africa in the west to Hawaii (🇺🇸 United States) in the east. The blue trevally is a moderately large fish, reaching a maximum recorded length of 70 cm, with distinctive features such as the number of rays in the second dorsal fin and its coloration aiding in its identification. Typically residing at depths of up to 60 meters, the blue trevally frequents reefs, beaches, lagoons, and sandy substrates. It is a predatory species, feeding on fish, prawns, crabs, and molluscs, although its reproductive biology remains largely undiscovered. The blue trevally holds varying degrees of importance to fisheries across its distribution range, with some regions reporting high catch volumes. It is also considered a gamefish and is prized for its culinary qualities.

This species is a member of the genus Carangoides, which includes a variety of fish commonly referred to as jacks and trevallies. Carangoides is a part of the Carangidae family, which falls under the order Carangiformes.

Characteristically, the blue trevally has a compressed, oblong body, with a dorsal profile that is more convex compared to the ventral profile. It differs from most other members of Carangoides by having a bluntly rounded snout similar to that of pompanos from the genus Trachinotus, accompanied by notably fleshy lips in adults.

In terms of appearance, the body of the blue trevally exhibits a blue-green to yellow-green color on the dorsal side, turning silvery beneath. Adults typically display five or six dusky vertical bands, which notably persist after death, and inconspicuous golden spots often adorn the sides, particularly above the pectoral fin area. The soft dorsal and anal fins present a pale yellowish-green hue, with anterior lobes displaying white to blue tips. The caudal fin is yellow-green, characterized by dark edges and tips, while the pelvic fins range from whitish to hyaline.

The distribution of the blue trevally covers wide swathes of the 🇮🇳 Indian, West Pacific, and Central 🌊 Pacific Oceans. Its range extends from the western reaches of 🇿🇦 South Africa, along the East African coast to the 🌊 Red Sea, continuing eastward to 🇮🇳 India, Southeast Asia, and further down to 🇦🇺 Australia and 🇮🇩 Indonesia. Further distribution includes regions up to 🇯🇵 Japan, Hawaii (🇺🇸 United States), and numerous Pacific islands such as 🇫🇲 Micronesia, 🇳🇨 New Caledonia (🇫🇷 Overseas France), and 🇹🇴 Tonga.

This species occupies coastal waters at depths reaching 60 meters, preferring environments over reefs, beaches, lagoons, and sandy substrates. It is primarily pelagic, allowing the species to traverse between islands and atolls, while its presence is uncommon in estuarine environments, indicating low salinity tolerance.

The biological and ecological attributes of the blue trevally are not thoroughly understood, with existing data primarily focused on its dietary habits. It is a swift predator that often forms small schools, preying on various small fish—including mackerel and filefish—along with crustaceans like prawns and crabs, sea lice, soft molluscs, and other soft-bodied prey. In Hawaii (🇺🇸 United States), observations indicate that they may follow foraging bonefish or goatfish, scavenging any uncovered edibles. This species appears to maintain a consistent abundance throughout the year, yet ripe individuals are seldom reported. Precise data on reproduction and growth remain unavailable, although the appearance of larvae off the 🇹🇼 Taiwan coast in February suggests a possible December spawning period. Juvenile blue trevallies have occasionally been seen seeking refuge among the tentacles of large pelagic jellyfish.

The blue trevally holds commercial significance in several regions due to its abundance, often being captured incidentally in major fisheries. Specific catch statistics for blue trevally are rarely maintained as it is generally grouped with other trevallies. Primary capture methods include hook and line, gill nets, and various types of traps. Notably, in 🇿🇦 South Africa, it is regarded as a popular gamefish amongst anglers, who achieve optimal catches during dawn and dusk, often utilizing small baits. While acclaimed for its culinary merit, rare instances of Ciguatera fish poisoning have been associated with this species.