Pollock roe
Mentaiko (明太子) is the marinated roe of pollock, and is a common ingredient in Japanese cuisine.
Mentaiko is made in a variety of flavors and colors and is available at airports and main train stations. It is usually eaten with onigiri, but is also enjoyed by itself with sake. A common variety is spicy mentaiko (辛子明太子, karashi mentaiko). It is a product of the Hakata ward of Fukuoka City.
Japanese style mentaiko was nominated as Japan's number one side dish in the Japanese weekly magazine, Shūkan Bunshun.