While it is important to note that there are no specific regulations from the FDA or other food agencies that govern sushi-grade fish products, there are some widely-accepted unofficial guidelines for this product.

One of the primary characteristics of sushi-grade fish (not just salmon), is that it has been frozen for a period of time to ensure that it is free of parasites. How long the fish is frozen depends greatly upon the type of fish.

As salmon is characteristically an oily fish, its quality will degrade if it is frozen gradually. To get around this problem, sushi-grade salmon is flash-frozen immediately after it is harvested. 

^{by [puamelia]}

Typically sushi-grade salmon must be frozen until solid and stored at -35C for at least 15 hours.

^{by Andrea Pokrzywinski}

Ensuring that the sushi you eat is sushi-grade is especially important, where salmon is concerned. As wild salmon spend part of their lives in fresh water, they are typically more susceptible to catching parasites in their flesh. In addition to the flash-freezing, sushi-grade salmon is also inspected to ensure that it is free of any infection. While it is relatively rare for such fish to be infected, it can happen. The processes that are characteristic of sushi-grade salmon, prevent such problems from ever reaching your plate.

In Conclusion

As you can see, there are many issues that affect the quality of the sushi, but when you eat sushi from a quality establishment, it is reasonable to expect that your sushi-grade salmon has been flash frozen and checked for parasites. Typically, if a restaurant does not mention that their products are “sushi-grade”, ensure that you ask how their meat is handled; especially where salmon is concerned.  But here are some general tips to observe when ordering Sashimi courtesy of "breakthroughsushi.com":

1. Color - clear color and texture usually means fresher
2. Shiny texture is a good sign for freshness
3. If you see what we sushi chefs refer to as "rainbow" which is a dark shiny rainbow like reflection on fish, it is a sign of old fish. This is mostly seen on tuna.
4. Smell - Avoid old fish smell. I am unsure how I could explain this, but, there is a difference between fresh fish and old fish (that is still servable as sashimi or sushi.)

Maximum Benefits of Sushi-Grade Salmon

After salmon is checked to confirm it follows sushi-grade guidelines, then it is time to reap the many benefits salmon has to offer. Our bodies are not able to make DHA and EPA omega-3 fatty acids. These fatty acids are very important to good brain and nervous system health, being linked to improved cognitive function.

Salmon is a great source of the fatty acids DHA and EPA, as well as protein. The proteins within salmon are beneficial to improving the strength and density of bones along with protecting against macular degeneration in the eyes. Salmon also contains Vitamin D, which when consumed in adequate amounts, reduces cardiovascular disease and cancer. Enjoy the delicious flavor and texture of sushi-grade salmon, while reaping all the benefits for your body.

"As with all fish consumption, sustainability is a major issue. Several varieties of salmon are sustainable and you can find more information at msc.org." - bbcgoodfood.com