Nigiri sushi (hand-pressed sushi) originally contained only fish in season at the time. However, in recent years technologies like freezing and fish farming mean that all kinds of fish are available year round, and the sense of what is in season has become dimmer. A fish is considered most delicious prior to egg-laying season, when its oil concentration increases.
At Japanese sushi restaurants, the names of fish are often written in kanji, which generally contain the element meaning "fish" and another element. For example, "魚" (fish) and "春" (spring) together create the kanji for "Spanish mackerel” (鰆), while elements meaning "魚" (fish) and "弱" (weak) make the kanji for "sardine" (鰯).
There are various types of sushi including "kakinoha-zushi" wrapped in persimmon leaves to enhance preservability, "oshi-zushi" stuffed in boxes and pressed, and "nare-zushi" made by fermenting fish. Among regional Kansai cuisine, Osaka Prefecture’s pressed mackerel sushi, Nara and Wakayama’s permission leaf sushi”, and Kyoto’s bo-zushi (rod shaped sushi) are very popular.
At a high-end sushi place, the price of the sushi is sometimes not written. In high-end places, it is a good idea to check the prices in advance or give the chef an idea of how much you want to spend.