n.
Any of more than 150 species of fishes (family Carangidae, order Perciformes) found in temperate and tropical portions of the Atlantic, Pacific, and Indian oceans and occasionally in fresh or brackish water.
Though body size and shape vary greatly, many species have small scales that create a smooth appearance, a laterally compressed body, rows of large spiky scales along the side near the tail fin, and a deeply forked tail. Many have a bluish green, silvery, or yellowish sheen. Jacks are important commercially and are favoured sport fishes. See also amberjack .