There are many things we Westerners don’t know about eating sushi, chief among them the fact that plain old soy sauce is actually not a very good match for most raw fish. Indeed, at a really good sushi bar, it’s often best not to use soy sauce at all.
As I explained at a Sushi Concierge dinner last night, that’s because a top-notch chef will season each piece of sushi for you as he makes it, using special sauces and garnishes that he’s created to match the subtle flavors of the different ingredients. In Japan, many high-level chefs will do this as a matter of course; in the U.S., you may have to ask, or shop around until you find a chef who’s willing to go to the trouble.
One of the primary types of special sauces that sushi chefs prepare is called nikiri. Last fall a food writer in Washington D.C. named Tim Carman read about nikiri in my book The Story of Sushi and asked me to accompany him to a sushi bar to get the real deal. Check out his very interesting report on nikiri here.
P.S. If you want to try making your own nikiri, I describe how to do it here. It takes some work, but it’s a far more interesting taste experience than plain old soy sauce.