Japan is blessed with an abundance of fish — drawn from the deep ocean to the coastal shores, lakes, rivers and streams. Making yourself familiar with the many kanji for different species of fish helps you get by when you run into all this slippery fare at a local restaurant, sushi counter or supermarket. Fish names, as they are spoken, existed before the introduction of kanji to Japan (beginning from the middle of the sixth century). The kanji names were chosen based on the characteristics of the fish — its appearance, how it swims, where it is found or when it is harvested — and bear no relation to the spoken form — for which the meaning has long been lost.
As for the kanji, let's start with the one for fish (魚, sakana), which looks a bit like one of our finned friends standing on its tail. This kanji often forms the first half of a particular fish name. Sometimes different kanji can be used to describe the same fish. Hirame (Bastard halibut), for example, can be written as both 鮃 and 平目. The fish takes this kanji because it is flat (平, taira).
Next, let's look at fish named after the seasons: