A mother and child buy catfish at a seafood market in Beijing June 29, 2007. The U.S. Food and Drug Administration (FDA) said on Thursday it would not allow imports of Chinese farm-raised seafood unless suppliers could prove the shipments contained no harmful residue. China is the largest producer of farmed fish, handling 50 percent of the total value of global aquacultured seafood exports around the world. It is also the third-largest exporter of seafood to the United States. REUTERS/Claro Cortes IV (CHINA)