Buy American. It matters when choosing seafood.
North American fisheries are among the most regulated and most sustainable in the world, especially when it comes to fish farming. Almost without exception, buying American seafood -- as opposed to fish and shellfish from other countries -- is the better choice in terms of freshness, health and sustainability.
Let me say at the outset that Canada and New Zealand do an excellent job with most of their fisheries, too, so in many cases Canadian or Kiwi seafood is also a good choice. In fact, there are examples where Canadian fisheries are better managed than those in the United States; Pacific rockfish is one.
Why Buy American? Start with jobs. There was a little flurry of advertising surrounding the Gulf shrimp industry after the hurricanes that destroyed New Orleans, but that has since drowned under a wave of cheap imported shrimp from Southeast Asia. Every shrimp you buy from Vietnam is one that could have helped a Louisiana or Mississippi shrimper get back on his feet.
Imported shrimp are perhaps the worst thing you can buy as a consumer, especially imported farmed shrimp. Shrimp farms in India, Vietnam, Malaysia and the like are horrible for the environment and should be avoided.
Farmed shrimp in the United States are more rare, but these shrimp farms are heavily regulated and the pollution they create just isn't in the same league as that seen in Southeast Asia.
Ditto for farmed tilapia, which is redundant because nearly all tilapia is farmed. Tilapia farms in Asia are more polluted and the fish are fed a poorer diet than those in the Southern states -- this means that Asian tilapia can have a nasty, muddy taste. American tilapia is often fed corn, which has its own health problems associated with it. But at least US tilapia farms are cleaner, as is the taste of their fish.
Farmed salmon is in the same boat. Salmon farming is illegal in most coastal states here, because these farms can potentially damage wild salmon stocks. Most of those that do have permits are in closed farms that don't connect to the sea. Canadian farmed salmon is problematic, but Chilean farmed salmon -- which is mostly what you see in markets -- is a disaster.
How about bay scallops? If you've eaten Chinese calico scallops, you probably won't ever want to again -- they are treated with a witch's brew of chemicals to keep them looking fresh. Buy American bay scallops when you can find them, and buy something else when you can't.
Likewise with tuna. Much of the tuna steaks you see coming from Vietnam or other places in the developing world has been treated with pure carbon monoxide. That's right: Your tuna could have been treated with carbon monoxide. So what? Well, doing this will keep a piece of tuna looking lovely even after it has spoiled. It is deceptive marketing, nothing more.
Swordfish stocks have rebounded in the US, but they're hurting in many other parts of the world. The national campaign to give swordfish a break worked here, so you can eat American sword with a good conscience.
The Bottom Line. Look at the label to see where your fish comes from. Cheaper isn't always better; in fact, it almost never is.