In supermarkets it's not even the fish - there's little to no nigiri in the case, and the rolls mostly contain little or even no fish. They're mostly rice, slat

In supermarkets it's not even the fish - there's little to no nigiri in the case, and the rolls mostly contain little or even no fish. They're mostly rice, slathered-on sauce, vegetables, and then maybe some fish (like breaded shrimp). You could theoretically order "fresh" (for whatever value of fresh the fish behind the counter is), but I'm not sure I've ever seen someone order instead of grabbing from the case. Perhaps "Americans don't know what good sushi tastes like" though.