I think here in Massachusetts, at least, there is regulation to the effect that fish sold to be served raw _must_ be frozen to kill parasites. Possibly it is species-dependent, but I would make a guess that it is not.

PS: turns out it is somewhat species dependent:

http://www.mass.gov/eohhs/docs/dph/environmental/foodsafety/...

This is true for some but not all species. Most fishmongers will not recommend eating salmon raw unless it has been deep frozen (and not just frozen in a typical residential freezer, which doesn't get cold enough), but most consider eating raw never-frozen tuna to be fine.

As with most things in life, it's really a question of risk and trade-offs. Parasites are rare enough in tuna that they are below the risk threshold for most people. Salmon less so, though it depends on where you get it and how much you trust them.

The broad guideline is that deep, open water, fast-moving fish have a lower parasite load than fish who live closer to shore, closer to the bottom, and/or don't move as fast.

Thus, tuna is pretty safe. But you're gonna want to cook an eel or a catfish before you stick it in your mouth.

One of the things I find fascinating about sushi but try not to think about too much, is that the clear implication is that all of the needed-to-be-frozen sushi I have eaten probably did have some parasites in it. I just ate dead parasites, which I admit is better than eating live ones. Safe, but still kind of gross.

A little off topic, but virtually all cigars imported into the US are frozen as well, usually by the distributors (there are a few companies who manage their own distribution who do not... like My Father / Tatuaje). This is to kill the tobacco beetle eggs that may be on the leaf. The exporters from Cuba also freeze their cigars before sale, but the cigars sold on the island itself (either name brands or custom rolls) are not. These beetles can cause thousands of dollars worth of damage very quickly.

There's actually no such thing as "sushi-grade" fish.

There is no standard or regulation that designates fish as "sushi-grade." It's a popular misconception.

I recently learned that “sushi-grade” is just a marketing term that has no meaning beyond simply “good grade”. It’s most often used by restaurants themselves. It’s not regulated or oficially defined in any way.

The article goes into some detail about the circumstances in which this is and isn't true (it's true for some fish from sources.)

Some of the poke places in LA use fresh tuna that was flown in from Hawaii. I think even the Costco poke is fresh. For those not familiar with poke, its a raw tuna , soy sauce and seaweed dish. You can remove parasites by sight easily.

I believe this is only necessary for salmon. Because they spawn inland they host parasites whose life cycle includes terrestrial animals, like bears and humans.