Tobiko is one kind of processed fish eggs.
Tobiko is the salted roe of the flying fish. Tobiko is smaller than salmon roe and an assembly of transparent, golden small spherical eggs. The size of each egg is 1 mm or so in diameter and the peel is so solid that chewing and bursting feelings are enjoyable. Tobiko is mainly used for sushi item and eaten in chirashizushi (vinegared rice topped with sliced raw fish, shrimp, egg, vegetables, and others) and gunkan-maki roll (vinegared rice topped with various ingredients rolled in a sheet of dried laver).
Tobiko' is also written as 'Tobikko,' but sold in the name of such as 'Tobiran' because 'Tobikko' is a registered trademark of the product by a fish processing company, Kanetoku (HQ is in Ashiya City, Hyogo Prefecture).
Nowadays there are many imported products from the southern waters such as Indonesia. They are processed into a product named "Golden caviar" which is used for canapes etc., and the black-colored products are used as artificial caviar.
Furthermore, there is also a substitute called 'Shishamokko,' which uses eggs of shishamo smelt.