Aji, also known as horse mackerel or saurel, is one of the three types of mackerel commonly available in sushi bars, the others being saba and sawara. The term aji refers to any member of the horse mackerel family. When aji is ordered in a U.S. sushi bar, what often arrives at the table is a tasty sample of Atlantic horse mackerel, or Trachurus trachurus. In Japan, however, aji is likely to mean ma-aji, or “true aji,” a different species of horse mackerel (T. japonicus). One may also encounter ma-aji in high-end U.S. sushi bars, especially on the West Coast. Also, be aware that aji may be advertised as “Spanish mackerel,” but true Spanish mackerel is actually called sawara.