Kizushi (salted blue-skinned fish) (きずし)
Kizushi refers to the salted blue-skinned fish. The chub mackerel is the most common, but other fish, such as Spanish mackerel, is also used. The kizushi of chub mackerel is the same as what is called shimesaba (salted and vinegared mackerel).
It seems that people in western Japan usually call it kizushi, while most people in eastern Japan call it shimesaba.
Although the name is referred as a sushi, it usually refers to the sliced fish served without rice. The slices, with further cuts sometimes made through the skin, are eaten with soy sauce, as are sashimi (sliced raw fish) or tataki (seared outside fish). Wasabi and ginger may be served with the kizushi. Sushi, having the kizushi on the top of rice is called kizushi zushi, saba zushi, or battera.
The most common way to make the kizushi is, to cut the head off, clean and fillet the fish, which is pickled in salt for about one night and then rinsed in vinegar. The length of the time to pickle, and the amount of salt and vinegar for the fish seem to vary depending on each recipes.
The kizushi is said to have originally been a preserved food and originated in that, the mackerel caught in the Japan Sea was cured in order to take it to the imperial capital. The Wakasa Kaido Road, connecting Wakasa Bay to Kyoto, was commonly called the Saba Kaido Road (Mackerel Road).
The Chinese characters for kizushi are also read "namazushi," in which case it refers to the ordinary sushi.