Double-Lined Mackerel

The double-lined mackerel (Grammatorcynus bilineatus) is a member of the Spanish mackerel tribe (Scomberomorini) within the Scombridae family. Commonly referred to as the scad mackerel, this species is predominantly found in the tropical and subtropical regions of the Indo-Pacific, extending from the 🌊 Red Sea to the Andaman Sea, and from the northern coast of 🇦🇺 Australia to the Ryukyu Islands (🇯🇵 Japan), reaching as far as 🇫🇯 Fiji.

These fish are associated with subtropical reefs and are oceanodromous, typically residing in open waters but are most frequently encountered at shallow depths ranging from 15 to 50 meters. Grammatorcynus bilineatus can attain a maximum length of approximately 100 centimeters (39 inches), although they more commonly measure around 50 centimeters (20 inches), and can weigh up to about 3.5 kilograms (7.7 pounds).

The double-lined mackerel features an elongated, slightly compressed body with small scales, a relatively small mouth, and large eyes. Its coloration includes a dark blue back, silvery sides, and a silvery-white belly. The species possesses two dorsal fins separated by a short gap. The fish is marked by having 11 to 13 dorsal spines, 10 to 14 dorsal soft rays, and 10 to 14 anal soft rays, while its pectoral fins are relatively short. Distinctively, it features two lateral lines: one along the dorsal profile and another at the level of the pectoral fins. Prior to 1983, it was occasionally misidentified as Grammatorcynus bicarinatus, the shark mackerel.

Grammatorcynus bilineatus primarily preys on crustaceans and fish, particularly Clupeiformes, such as Sardinella and Thryssa species, but it also consumes other fish such as triggerfishes (Bali (🇮🇩 Indonesia)stes) and barracudas (Sphyraena). The species is known for forming large schools.