Aji or Ma-aji. Japanese horse mackerel (Trachurus japonicus). Also called "Japanese jack mackerel."
Can grow to 40 cm, but usually smaller, 13-17 cm. Large eyes, projecting lower jaw, curved lateral line of hard scales. Tail in V-form. Fast swimmer. Lives both near bottom, in midwaters and near the surface. Feeds on crustaceans, shrimps and small fishes.
Found in waters around Japan, Korea and in the East and South China Seas.
May to September, best in summer, when the fat content is highest thanks to the spawning season.
A favorite on Japanese menus since the Nara Period and still going strong - aji is popular and inexpensive. Not for nothing is the name "aji" a homonym for "taste." The character with which it is written combines the formal character for "three" with "fish," indicating that it was traditionally caught in the third month (May in the modern calendar). Aji has delicious, oily flesh with lots of DHA and amino acids. Can be served in a wide variety of ways: on sushi (either fresh or marinated in vinegar and salt), as sashimi, tataki, grilled, deep fried, or (the smaller fish) marinated.