Fuqing (pronounced foo-CHING) is at the top of the list this year for refused shipments of seafood from China, with 43 rejections through November, according to records kept by the United States Food and Drug Administration. All of those rejections involved the use of illegal veterinary drugs.

By comparison, Thailand, also a major exporter of seafood to the United States, had only two refusals related to illegal veterinary drugs. China as a whole had 210 refusals for illegal drugs.

“For 50 years,” said Wang Wu, a professor at Shanghai Fisheries University, “we’ve blindly emphasized economic growth. The only pursuit has been G.D.P., and now we can see that the water turns dirty and the seafood gets dangerous. Every year, there are food safety and environmental pollution accidents.”

Environmental problems plaguing seafood would appear to be a bad omen for the industry. But with fish stocks in the oceans steadily declining and global demand for seafood soaring, farmed seafood, or aquaculture, is the future. And no country does more of it than China, which produced about 115 billion pounds of seafood last year.

China produces about 70 percent of the farmed fish in the world, harvested at thousands of giant factory-style farms that extend along the entire eastern seaboard of the country. Farmers mass-produce seafood just offshore, but mostly on land, and in lakes, ponds, rivers and reservoirs, or in huge rectangular fish ponds dug into the earth.

“They’ll be a major supplier not just to the U.S., but to the world,” said Richard Stavis, the chairman of Stavis Seafoods, an American company that imports Chinese catfish, tilapia and frog legs.

China began emerging as a seafood power in the 1990s as rapid economic growth became the top priority in the country. But environmental experts say that headlong pursuit of higher gross domestic product has devastated Chinese water quality and endangered the country’s food supply. In Guangdong Province in southern China, fish contaminated with toxic chemicals like DDT are already creating health problems.