What is Sushi Grade Fish?
Firstly, you should keep in mind that there really is no such food grade as sushi grade fish. For a detailed treatise on what really makes a piece of fish sushi grade, I recommend reading the section of SushiFAQ which answers this question, What is sushi grade fish? However, what this term really means is that the fish is fresh and handled properly enough that one can be reasonably sure that it is clean and parasite free. In most cases it has been frozen to a low enough temperature for long enough that any parasites that the fish may have had have been destroyed. Most fish that you will find in any grocery store or fish market is not sushi grade fish, so ask questions and know what you are buying if you intend to eat any seafood raw.