The giant trevally, Caranx ignobilis (also known as the giant kingfish, lowly trevally, barrier trevally, ulua, or GT), 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.
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, however 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 (5 1/2 feet) and a weight of 80 kg (176 pounds). 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.
At sizes less than 50 cm (1.6 feet), the giant trevally is a silvery-grey fish, with the head and upper body slightly darker in both sexes. Fish greater than 50 cm show sexual dimorphism in their colouration, with males having a dusky to jet black body, while females are a much lighter coloured silvery grey. Individuals with a darker dorsal colouration often also display striking silvery striations and markings on the upper part of their body, particularly their back. Black dots of a few millimetres in diameter may also be found scattered all over the body, although the coverage of these dots varies between widespread to none at all. All the fins are generally light grey to black, although fish taken from turbid waters often have yellowish fins, with the anal fin being the brightest. The leading edge and tips of the anal and dorsal fins are generally lighter in colour than the main fin. There is no black spot on the operculum. Traces of broad cross-bands on the fish’s sides are occasionally seen after death.