China will step up inspections on the use of antibiotics in fish farms, including chemicals that can cause cancer, after contaminants caused trading partners to block its seafood exports.

. The ministry said last month that malachite green, a cancer-causing chemical used by fish farmers to kill parasites, had been found in some food samples, as well as nitrofurans, an antibiotic also linked to cancer.

China is the largest producer of farmed fish, handling 50 percent of the total value of global aquacultured seafood exports around the world. Its top export market for seafood is Japan, and it is also the third-largest exporter of seafood to the United States.

Last month, the US Food and Drug Administration said a sampling of imported Chinese seafood from October 2006 through May 2007 found more than 15 percent of shipments were contaminated with antimicrobial agents that are not appropriate for use in farm-raised seafood .