Longfin Trevally

The longfin trevally has a similar body profile to most other jacks, having a deep, strongly compressed body. It is a medium-sized fish, growing to a maximum known length of 57 cm, and at least 3.5 kg in weight. The profile of the head is very steep from the mouth to the nape, especially in adults. There is a weak adipose eyelid covering the eye, which is about equal to or smaller than the snout length. Both jaws are lined with villiform teeth, although larger specimens have small conical teeth in bands. The gill rakers are one of the diagnostic features of the species, having 30 to 37 rakers on the first arch. The dorsal fin is in two parts, the first consisting of 13 spines and the second of 1 spine followed by 19 to 22 soft rays. The second dorsal fin is sexually dimorphic, with mature males longer than 21 cm having 3 to 12 of the central soft rays extended into thin filaments of varying lengths. The anal fin has 2 anteriorly detached spines followed by a single spine connected to 16 to 18 soft rays. The lobes of both the anal and dorsal fin are highly extended, giving the species its name. The anal fins also show extension into filaments to a lesser degree. The pectoral fins are falcate to subfalcate with 18–20 rays, while the caudal fin is deeply forked with bilateral, paired caudal keels. …

The longfin trevally inhabits tropical to subtropical waters of the Indian and west Pacific Oceans. It is distributed from East London, South Africa in the west, north to Madagascar, eastern Africa, India, Thailand, Hong Kong, Taiwan and to Japan in the east. The species is also common in the Red Sea and the Gulf of Oman. The species inhabits inshore coastal waters rarely venturing offshore, and is pelagic, inhabiting both the upper and lower sections of the water column. Longfin trevally are commonly found on rocky and coral coastlines, often inhabiting reef complexes, with solitary individuals or groups of larger fish patrolling the edges of reefs. They are also found in shallow, sandy bays and lagoons, with juveniles known to enter and use estuaries as nursery areas.