These subtropical reef-associated and oceanodromous fishes usually inhabit open water but they are mostly found in shallow waters at depths of 15 to 50 m.[4]
Grammatorcynus bilineatus can reach a maximum length of about 100 centimetres (39 in), with a common length of about 50 centimetres (20 in) and maximum weight of about 3.5 kilograms (7.7 lb).[5][6]
The double-lined mackerel has an elongated and slightly compressed body covered with small flakes with a relatively small mouth and large eyes. The body color is dark blue on the back, silvery on the sides, silvery white on the belly. The dorsal fins are two, separated by a short space. These fishes have eleven- thirteen dorsal spines, ten- fourteen dorsal soft rays and ten-fourteen anal soft rays. The pectoral fins are rather short. There are two lateral lines, one on the dorsal profile, and the other at the height of the pectoral fins.[4][7]
Grammatorcynus bilineatus mainly feed on crustaceans and fishes, especially Clupeiformes (Sardinella and Thryssa species), but also other fishes such as triggerfishes (Balistes) and barracudas (Sphyraena). It usually forms large schools.[citation needed]
^Collette, B.B., 2001. - Scombridae. Tunas (also, albacore, bonitos, mackerels, seerfishes, and wahoo). - FAO species identification guide for fishery purposes. K.E. Carpenter and V. Niem (eds.)
^Collette, B.B. and C.E. Nauen, 1983. - Scombrids of the world. An annotated and illustrated catalogue of tunas, mackerels, bonitos and related species known to date - FAO Species Catalogue. Vol. 2.
^Collete, B.B. 1986. - Scombridae. - In P.J.P. White head, M.-L. Bauchot, J.-C. Hureau, J. Nielsen, and E. Tortonese (eds.), Fishes of the North-eastern Atlantic and the Mediterranea. Vol II, pp. 981-997. UNESCO, Paris
