Take a look at this video about purchasing fish at the market.  This video explains the chemicals that are in fish that is being shipped to the U.S from China.  It is not only a problem in China but all asian countries.  When purchasing fish I never buy fish if has come from any asian country.  Seafood is not tested for chemicals when brought to the U.S.  When you buy fish it should say exactly what country it has come from. There is another video besides this one that I am trying to locate that goes into detail about the chemicals in fish from Asia.  When I locate it I will put it up.  The type of chemicals that are being used are so dangerous that it is not worth risking your health to get the health benefits from eating fish.  If you know anyone who eats fish then pass this video on.