them have been shown to cause cancer when fed to laboratory animals for `` prolonged periods of time , '' Acheson said . Alerts have been issued in the past , but Thursday 's announcement is the largest . The food will not be allowed into the United States until the importer can prove it is free from harmful contaminants , Acheson said . He said the agency decided to broaden its previous alerts for products from individual companies to a countrywide alert after tests showed that 15 percent of those species of seafood produced by 18 companies in China contained traces of one or more of the contaminants . `` FDA is taking this action to protect the public health of the American people , '' he said . Watch more on the FDA 's import alert on five kinds of fish from China . '' The products `` could cause serious health problems if consumed over a long period of time , '' he said . Still , Acheson added , the low levels of contaminants means that there is `` no imminent threat '' to the public health . China is the world 's largest producer of
ROCKVILLE , Maryland -LRB- CNN -RRB- -- The U.S. Food and Drug Administration on Thursday announced it is blocking the import from China of five species of seafood until their importers can prove they are not contaminated . About 10 percent of catfish eaten in the U.S. comes from China , according to the National Fisheries Institute . `` FDA is initiating an import alert against several species of imported Chinese farmed seafood because of numerous cases of contamination with drugs and unsafe food additives , '' said Dr. David Acheson , the agency 's assistant commissioner for food protection , in a conference call with reporters . The species cited are catfish , eel , shrimp , basa and dace , he said . Basa is similar to catfish ; dace is similar to carp . The medications cited include the antimicrobials nitrofuran , malachite green , gentian violet and fluoroquinolones . Nitrofuran , malachite green , and gentian violet have been shown to cause cancer in laboratory animals . Use of fluoroquinolones in food-producing animals can result in antibiotic resistance . None of them is approved for use in farmed seafood in the United States and some of