Giant trevally
(Caranx ignobilis)

The giant trevally (Caranx ignobilis), also known as the lowly trevally, barrier trevally, giant kingfish or ulua, is a species of large marine fish classified in the jack family, Carangidae.

The giant trevally is distributed throughout the tropical waters of the Indo-Pacific region, with a range stretching from South Africa in the west to Hawaii in the east, including Japan in the north and Australia in the south. Two were documented in the eastern tropical Pacific in the 2010s (one captured off Panama and another sighted at the Galápagos), but it remains to be seen if the species will become established there.

The giant trevally is distinguished by its steep head profile, strong tail scutes, and a variety of other more detailed anatomical features. It is normally a silvery colour with occasional dark spots, but males may be black once they mature. It is the largest fish in the genus Caranx, growing to a maximum known size of 170 cm (67 in) and a weight of 80 kg (176 lbs). The giant trevally inhabits a wide range of marine environments, from estuaries, shallow bays and lagoons as a juvenile to deeper reefs, offshore atolls and large embayments as an adult. Juveniles of the species are known to live in waters of very low salinity such as coastal lakes and upper reaches of rivers, and tend to prefer turbid waters.

The giant trevally is an apex predator in most of its habitats, and is known to hunt individually and in schools. The species predominantly takes various fish as prey, although crustaceans, cephalopods and molluscs make up a considerable part of their diets in some regions.

The giant trevally employs novel hunting strategies, including shadowing monk seals to pick off escaping prey, as well as using sharks to ambush prey. Footage released in 2017 on Blue Planet II revealed a group of approximately 50 giant trevally hunting terns, specifically fledglings still learning to fly and which crash land in the water, as well as both fledglings and adults unfortunate enough to fly low enough for the fish to pounce on them, in Farquhar Atoll in the Seychelles.

The giant trevally reproduces in the warmer months, with peaks differing by region. Spawning occurs at specific stages of the lunar cycle, when large schools congregate to spawn over reefs and bays, with reproductive behaviour observed in the wild. The fish grows relatively fast, reaching sexual maturity at a length of around 60 cm at three years of age.