Again, it's up to the individual. Some Buddhist sects teach that it's permissible to eat meat as long as the animal is not slaughtered and butchered specifically for you, and you don't see it being done. Much of Japan traditionally relied on seafood, and Japan is heavily Buddhist. I think the same can be said of much of southeast Asia. China was (and probably still is) primarily Buddhist and relied on pigs, chickens and ducks, not to mention sea creatures along the sea coasts and rivers. Consider, however, that fish and other forms of sea creatures may very well feel pain, and die suffering. There is a way to cause instantaneous death to a fish, but given the volume of fish caught, most of them simply suffocate. Watch any Deadliest Catch tv show, or tv commercial for Gorton's, McDonald's or Red Lobster and see how they are dumped from the nets into holding tanks. Oysters are typically eaten alive. The sound made as a lobster is plunged into boiling water is not a vocalization of pain, but rather, air being expelled. However, this is not to say the lobster doesn't feel pain. I myself still eat seafood, though I may very well move away from it knowing now what I know.
It has something to do, from what I understand, with how they affect the lungs, but I don't think there's anything to that, really.
