....yeah I see that at my grocery too. The state health department here warns not to eat shrimp from Southeast Asia because of antibiotic and fertilizer contamination, so you're right...
What I have also read is that a lot of the seafood that states it is from Vietnam and other countries is in fact from China. It gets shipped into Vietnam and then repackaged product of Vietnam. This is because people will not buy it IF it says it is coming from China.
I have read they have chickens in cages over the water where the shrimp/fish are caged. Therefore, the shrimp/fish are eating the droppings from the chickens. This is why I never eat ANY seafood that is not wild. I pass on ALL farm raised seafood, especially if it not from the US, Canada or one of the Scandinavian countries