Jacks (family Carangidae) are tropical and subtropical open water marine fishes found in the Atlantic, Pacific and Indian Oceans. Their body, generally silver in color, has a very streamlined shape, being slightly elongated and somewhat laterally compressed. Both the dorsal and anal fins are short, the latter having two spines. The base of the tail is thin and often the scales of this region are modified to form a kind of spines called scutes. The caudal fin of the Jacks is strongly forked, making them strong and very fast swimmers.
They are clearly predatory species, ranging in size from 30 cm for mackerels to over 170 cm in length for the giant horse mackerel Caranx ignoilis. Jacks often form large schools and can travel very considerable distances. Very voracious predators, Jacks feed mainly on other fish, and to a lesser extent on molluscs, crustaceans and planktonic invertebrates.
Within the Carangidae family we find 147 species classified into 4 subfamilies: Trachinotinae (with 2 genera and 21 species), Scomberoidinae (3 genera and 10 species), Naucratinae (5 genera and 13 species), Caranginae (20 genera and 103 species). Some of the Jacks species are of great economic importance to humans because of their culinary interest.
The reproduction of Jacks is by external fertilization, with the release of gametes into the water column, forming floating planktonic eggs, which are disseminated by currents.