【Reading】ぜいご

【English Name】Scute

Zeigo refers to the hard, spine-like scales arranged in a single row on the lateral side near the tail fin of horse mackerel (aji). In ichthyology they are called "ryorin" (keeled scales), and they are sometimes written as "junjorin" (scute scales). In English they are called "scutes," deriving from the Latin word for shield.

Among bony fishes, they are a characteristic structure possessed only by fish of the subfamily Caranginae of the family Carangidae in the order Perciformes, and are thought to be formed by the transformation of ordinary scales. They are arranged in a band from the tail side toward the body side along the lateral line, and because the number and size differ by species, they also serve as a clue for distinguishing horse-mackerel species.

There are various theories about their role, including a theory that they have a defensive function to protect the body when attacked from behind by a large fish, and a theory that they are involved in controlling water flow during swimming. However, none has reached an established conclusion.

When handling horse mackerel as sushi or sashimi, removing the zeigo is a basic step of preparation. The reason is that, being hard, they spoil the texture, and they are removed by laying the knife flat from the tail side and sliding it toward the head. It is an indispensable step for beautifully finishing horse-mackerel nigiri and hikari-mono (silver-skinned fish).