Ma-aji, Horse Mackerel or Japanese Jack Mackerel

Aji migrate through the warmer waters of the world’s oceans in such large schools—numbering from several hundred to thousands of fish— that fishermen say if you catch one, you will fill your bucket over and over again in a few minutes.

In Japanese waters alone, there are about twenty horse mackerel species. Among them are ma-aji, “true horse mackerel,” which at sushi restaurants is called simply aji. Caught at about 6 to 15 inches long, ma-aji has glittering silver-blue skin with a thorny strip of scales running from just behind the gills all the way to the tail. The scale strip, which becomes quite spiky toward the tail, is always removed before the fish is prepared.