ROCKVILLE , Maryland ( CNN ) -- 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 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 farmed fish , accounting for 70 percent of the total produced , he said . It is the third-largest exporter of farmed fish to the United States . The action is an import alert , which means that these products from Chinese processors `` will be detained and refused entry into the United States until the importer can demonstrate that the product is safe and in compliance with applicable regulations , '' said Margaret O ' K. Glavin , FDA 's associate commissioner for regulatory affairs . Last year , the FDA slapped a countrywide alert on all Chinese eel after tests showed residues of an antimicrobial agent , she said . Since then , and `` despite extensive communications between FDA and appropriate Chinese authorities to correct the problem , we have continued to find residues of certain veterinary drugs or food additives that are not permitted for use in the United States , '' she added . Glavin said the FDA inspects 5 percent of seafood from China . The first alert on Chinese seafood occurred before 2001 , she said . `` We 're not asking for this product to be withdrawn from the market or for people to take this out of their freezers and throw it away , '' Acheson said . `` This is a long-term health concern ; it is not an acute health concern . '' China is not the sole offender , Glavin said . Import alerts have been ordered for firms in the Philippines , Mexico `` and several others , '' though this is the first countrywide import alert , she said . More than 80 percent of shrimp eaten in the United States is imported , including 7 percent from China , according to the National Fisheries Institute . About 10 percent of catfish eaten in the United States comes from China , the seafood industry advocacy group said . Last year , the United States imported 590,299 metric tons of shrimp from abroad ; 68,150 metric tons of which came from China , according to the Department of Commerce . The United States imported $ 1.2 billion of fish from China in 2004 , according to H. M. Johson & Associates , a seafood industry research group . E-mail to a friend .
FDA blocks import of shrimp , catfish , eel , basa and dace from China . Fish wo n't be allowed until importers prove they are safe . The fish were treated with antibiotics and antifungal medication . The antibiotics are not allowed in U.S. fish .