THURSDAY, June 28 (HealthDay News) -- Troubles with tainted products from China continued Thursday, as U.S. health officials halted the import of farmed seafood from that country.

"The FDA is not allowing the import of these Chinese farmed seafood products until the importers can prove that the seafood is free from harmful contaminants," Dr. David Acheson, the U.S. Food and Drug Administration's assistant commissioner for food protection, said during an afternoon teleconference.

He identified the banned fish as catfish, basa (similar to catfish), shrimp, dace (similar to carp) and eel, which he said may contain chemicals that are potentially carcinogenic.

"The FDA will start to detain these products at the border until the shipments are proven to be free of residues from drugs that are not approved in the United States for use in farm-raised fish," Acheson said.

However, he added, "there is no imminent threat to the public health, because of the low levels of contaminants. But the banned substances could cause serious health problems if consumed over a long period of time -- years."

"FDA is taking these actions because there have been continued violations with no signs of abatement," he said. "We have seen the involvement of a number of exporters, so we have seen the need to broaden this to a countrywide alert."

The action follows reports Wednesday that 900,000 tubes of toothpaste imported from China contaminated with chemical used in antifreeze were found in institutions for the mentally ill, hospitals, prisons and juvenile detention centers in Georgia and North Carolina, according to The New York Times.

Also this week, regulators in China closed 180 food plants after uncovering more than 23,000 food safety violations. Despite the crackdown, China denies that its food exports are dangerous.

All of that was preceded by the largest pet food recall in U.S. history because of tainted additives from Chinese companies.

In the current case, the FDA doesn't know how much of the U.S. supply these fish from China represent, Acheson noted.

Approximately four-fifths of the seafood consumed in this country is imported from about 62 countries, according to the FDA's import alert.

China remains the biggest producer of aquacultured seafood in the world, accounting for 70 percent of the total production and 55 percent of the total value of aquacultured seafood exported worldwide.

China is also the No. 3 exporter of seafood to the United States, the agency noted. Shrimp and catfish products are two of America's top 10 most-consumed seafood products.

The contaminants found in the fish are the antimicrobials nitrofuran, malachite green, gentian violet, and fluoroquinolone. Nitrofuran, malachite green and gentian violet, which are used to treat fungal infections, have been shown to be carcinogenic with long-term exposure in lab animals. The use of fluoroquinolones in food animals may increase antibiotic resistance to this class of antibiotics.

Fish farmers in China are purposely adding these chemicals to the fish feed and water to deal with fungal and bacterial infections, Acheson said.

"None of these substances is approved for use in farm-raised seafood in the United States, and the use of nitrofurans and malachite green in aquaculture is also prohibited by Chinese authorities," Acheson said.

Incidents of contamination of Chinese farmed fish go back at least six years. "There have been problems with farmed fish products produced in China and exported to the U.S. since 2001," Margaret O' K. Glavin, FDA's associate commissioner for Regulatory Affairs, said during the teleconference.

In 2006, the FDA placed a countrywide alert on all Chinese eel due to residues of malachite green, Glavin said.

Import bans on farm-raised fish are not limited to China. "There are import bans on farm-raised fish from particular manufactures in other countries," Galvin said.

The current FDA's alert is based on an increased monitoring of imported seafood. From October 2006 through May 2007 the FDA found residue of unapproved animal drugs and/or unsafe food additives in seafood imported from China.

During that time, the FDA tested 89 samples consisting of catfish, basa, shrimp, dace and eel from China. Of these, 25 percent were found to contain drug residues. These included nitrofurans detected in shrimp, malachite green detected in dace, eel and catfish and basa, and gentian violet detected in eel and catfish. In addition, fluoroquinolones were found in catfish and basa. Chinese authorities have acknowledged permitting the use of fluoroquinolones in aquaculture, according to the import alert.

The import alert will remain in effect until the manufacturers can prove to the FDA that their fish are clear of any harmful chemicals, Glavin said.

For people who have these products in their home, the FDA is not recommending destroying them or returning them. In addition, the agency is not recalling Chinese farmed fish from retail stores or restaurants.

Spanish-speaking people can call the Su Familia Health Helpline, at 1-866-783-2645, to have any questions answered. The national helpline offers free health information in Spanish and English, and is available from 9 a.m. to 6 p.m.(EST) Monday through Friday. The helpline is sponsored by The National Alliance for Hispanic Health.

More information

For more information on banned fish from China, visit the U.S. Food and Drug Administration.

SOURCES: June 28, 2007, teleconference with Margaret O' K. Glavin, associate commissioner, Regulatory Affairs, and David Acheson, M.D., assistant commissioner, Food Protection, U.S. Food and Drug Administration, Rockville, Md.