In Japanese culture, fish are so important that many change their names as they grow, and this is one of them.
4-5 cm (1.6-2 inches) = Shinko
around 10 cm (3.9 inches) = Kohada
more than 15 cm (5.9 inches) = Konoshiro
Edo (=Tokyo) people cannot go through one summer without having some Shinko - It is almost one of the symbol of summer overthere.
As you can imagine by its size, Shinko requires a lot of work to the chagrin of the sushi chef. But we can also say that it is a fish that showcases the skill of the chef.