The Safe Food Handbook (now in its second edition) argues that it is best to avoid imported seafood, on which the U.S. and Canada are increasingly dependent.
The reason: it can be unsafe to eat. Sanitation controls in the countries from which most of this seafood now comes from are often weak, and the fish-growing environment is very polluted. Personally, I no longer eat imported shellfish products in any form. When eating out, I ask where the shellfish came from. If the restaurant can't or won't give me an answer, I pass.
Recent events in the U.S. have confirmed my concerns. The U.S. Food and Drug Administration (FDA) has had to remove all Korean certified shippers of molluscan shellfish from the Interstate Certified Shellfish Shippers List (ICSSL). That is, they are no longer allowed into the U.S. (That goes for fresh, frozen and processed products). Some companies, such as Crown Prince Seafood of South Korea, are conducting huge product recalls.
Why? Without going into the unpleasant details, let's just say that the shellfish has been found to come from areas that are heavily polluted by human waste. Among other things, norovirus has been found in the shellfish, and that is probably not the end of it. And I would bet that Korea is not the only country where this happens (see the book for more..) Is "oysters a la poop" really what you want to eat?
To your good health,