Originally Posted by MikeFromTokyo

Proper sushi fish and shell fish, etc... must NEVER be frozen. It is stored in refrigerators that are calibrated to temperatures very close to freezing, but it must not actually hit 0 degrees celsius.

Shell fish are actually still alive when you eat them, and shrimp are alive until they are boiled. In tempura, such ingredients are equally fresh and still alive until they are fried, i.e. moments before eating.

IMO proper sushi is rarely found outside of Tokyo.