Sushi's not all tuna and salmon, far from it
Laurel Fan/Flickr Saba (a type of mackeral), a traditional sushi fish
The Atlantic has a great, eye-opening article on sushi in its June issue. While the point of the article is ostensibly that the "new face of sushi" in the United States "isn't always Japanese, or even Asian," what's really kind of more cool about the article, I think, is its details about traditional sushi-eating.
Maybe everyone's been to Japan and knows this already, but "sushi" can refer to "just about any dish that includes rice seasoned with vinegar, sugar, and salt," the article says, and is, traditionally, eaten around the sushi bar, "while the chef, a convivial character who knew many of his patrons, would suggest dishes based on the seasonal and local delicacies he had purchased that morning."
And all that tuna and salmon you see on sushi menus? "[N]one adheres to the Japanese practice of highlighting local, seasonal ingredients," the Atlantic writes. The most traditional sushi fish, the article says, is a type of mackeral called saba. The article is also a who's who of inventive, cutting-edge sushi chefs in the U.S.