A species of mackerel. Sold in Japan as Taiseiyou saba (literal translation from English), Norwegian mackerel (Norway saba), or simply mackerel (saba, a general term for Scomber, Rastrelliger and Grammatorcynus). Also known as Boston mackerel or Scottish mackerel.
"The Atlantic mackerel's body is elongate, steel-blue marked with wavy black lines dorsally and silvery-white ventrally, its snout long and pointed. It possesses two spiny dorsal fins, which are spaced far apart, two pectoral fins, and small caudal and anal fins, also spaced far apart." 
-  Wikipedia entry