The frozen shrimp, catfish and eel arrived at U.S. ports under an "import alert," which meant the FDA was supposed to hold every shipment until it had passed a laboratory test.
But that was not what happened, according to an AP check of shipments since last fall. One of every four shipments the AP reviewed got through without being stopped and tested. The seafood, valued at $2.5 million, was equal to the amount 66,000 Americans eat in a year.
FDA officials stuck the pond-raised seafood on their watch list because of worries it contained suspected carcinogens or antibiotics not approved for seafood.
No illnesses have been reported, but the episode raises serious questions about the FDA's ability to police the safety of America's food imports.
"The system is outdated and it doesn't work well. They pretend it does, but it doesn't," said Carl R. Nielsen, who oversaw import inspections at the agency until he left in 2005 to start a consulting firm. "You can't make the assumption that these would be isolated instances."
If the system cannot stop known risks, Nielsen said, how can it protect against hidden dangers, such as the ingredients from China that made toothpaste potentially poisonous and killed dozens of pets earlier this year?
China is America's biggest foreign source of seafood, the 1.06 billion pounds it supplied in 2006 accounting for 16 percent of all seafood Americans buy.
President Bush has asked a Cabinet-level panel to recommend better imported food safety safeguards. Chinese officials have promised to inspect fish farms closely for the use of drugs and chemicals, even as they called the FDA's testing mandate illegal under world trade rules.
FDA officials acknowledged that some shipments slip through import alerts, but said overall they work.
"Any time you introduce a human element into something, I don't think you can necessarily guarantee 100 percent," said Michael Chappell, the official responsible for field inspections and labs.
Normally, the FDA inspects just 1 percent of the cargo it oversees. When goods land under an import alert, however, they are considered guilty until proven innocent: All shipments are supposed to be held until private tests that cost importers thousands of dollars show the seafood is clean. Sometimes, the FDA double-checks those tests in its own labs. Products can be detained for months, irking importers.
However, a shipment can escape inspection if, for example, a company uses a name or address not on an import alert, Chappell said. That appears to be what happened in one case AP found.
Also, FDA workers who must review hundreds of shipments that flash across a computer screen each day may miss some tagged for testing.
The agency has about 450 budgeted positions for screening approximately 20 million shipments annually of such things as fish, fruit and medical devices. At a congressional hearing last month, FDA employees doubted whether they have the resources to do the job.
Last summer, FDA labs began accumulating evidence that 15 percent of farm-raised shrimp, eel and catfish contained dangerous or unapproved substances. The agency started throwing individual companies on its watch list, and ultimately issued a sweeping mandate that all shrimp, eel and catfish raised on Chinese farms be stopped and tested.
Federal food safety officials said that while the seafood poses no immediate danger, long-term exposure could increase the risk of cancer or undermine the effectiveness of drugs used to fight outbreaks of disease.
The FDA did not tell shoppers to throw away what they had bought; agency officials said they simply had to get control over what China was sending.
Seafood that clears the ports enters a vast distribution system that includes restaurants, wholesalers and brand-name packagers.
The Chinese government and U.S. importers say the FDA overreacted. It would be impossible, importers say, for a person to eat enough seafood to be affected by the trace levels that FDA found of substances such as the antifungal chemical malachite green and the antibiotic Cipro.
The AP reviewed 4,300 manifests of seafood shipments from China compiled by Piers Reports, a company that tracks import-export data, and found 211 shipments that arrived under import alert since last fall.
FDA officials refused to identify exactly which shipments were tested, saying they were too busy to do so.
So the AP contacted importers directly, talking to 15 companies responsible for 112 of the 211 shipments. Eleven said their products were tested; four said the FDA did not bother to stop a total of 28 shipments weighing 1.1 million pounds. Virtually all the shipments entered through ports in the Southeast, including Tampa, Fla., Miami and Savannah, Ga.
The importer with the most cases was Florida-based Tampa Bay Fisheries.
Chief executive Robbie Paterson said 23 shipments of breaded or dusted frozen shrimp delivered between October and May were not inspected. In rare cases, the FDA removes from its watch list companies that have passed five straight tests. Paterson said he assumed that was why Tampa Bay's shipments went through.
Not so: Tampa Bay's shrimp supplier -- the Fuqing City Dongyi Trading Co. -- was on the watch list.
Three other companies said a total of five shipments of catfish, eel or shrimp were not stopped and tested.
Like many others in the importing business interviewed for this story, Paterson said he believed that import alerts were completely effective and that Chinese seafood poses no health risk.
FDA officials "are diligently doing the inspections as they see fit," Paterson said.
The expanded testing mandate has rattled China. U.S. importers said they are being told that the government is holding back shipments until tests show they will pass U.S. muster. The disruption has yet to result in any substantial price increases in the United States.
"I don't really know why they conducted the special test on our products," said a woman who identified herself as Miss Lin, a spokeswoman for Shantou Red Garden Foodstuff, which the FDA placed on its watch list in April after finding its dusted shrimp contained nitrofurans, an antibiotic that may cause cancer. "We've been exporting products to the U.S. for many years and we respect their standards and we meet their standards."