The mackerel is best from autumn through winter. It is cured since it spoils very quickly.
It is not an expensive fish,and due to its strong fishy taste, it is not favored by everyone. It is high in oil, and has a strong scent due to a high trimethylamineN-oxide content, or TMAO which is used for water balance in cells for most sea animals.
While the taste of mackerel is delicious, this fishy scent is the culprit which gives mackerel a bad name. TMAO is contained in the cells, and is water soluble,so the salting phase in the curing process releases a fair amount of it due to osmosis. It is one of the few fishes that still taste good after it is cured by salt and vinegar.
While extra precautions are made, it is considered a delicacy when served raw for its creamy rich texture. Extra fresh mackerel does not have a fishy scent, but they have to be brought in live in order to enjoy it raw.
Cities like Kyoto, which are geographically far from the ocean, have many different types of regional sushi that use cured or salted fish. The main reason for this trend is that fresh fish was unavailable back in the days when refrigerators did not exist, and they only had the option of buying cured fish. Mackerel is one of the best ingredients for cured fish in Japan. Kyoto is famous for using mackerel for their primitive nare sushi as well.
The name saba is believed to be derived from the word isaba, means discolored leaves due to the autumn season, which is when the mackerel starts to taste good. The “i” eventually disappeared and the name saba became mainstream.