BEIJING, Nov. 22 (Xinhua) -- The sales ban on turbot in Beijing and other cities reflects loopholes in food safety monitoring, according to Cao Jilin, the man who introduced the flatfish to China, and other experts.

    "There is no quality control before the fish enter the market, even though government departments are supposed to do that," said Cao, member of the Chinese Academy of Sciences and a researcher with the Yellow Sea Fishery Research Institute of Chinese Academy of Fishery Sciences.

    In fact, China has watchdogs for every step in fish farming, from the production of fish feed, the use of drugs, breeding, right through to sales, according to Cao. However, some local watchdogs are either doing their jobs poorly or not doing their jobs at all.

    Taiyuan followed Beijing in introducing the ban on Monday, after Shanghai announced Friday it had detected carcinogens in the fish. Shanghai and cities in Zhejiang Province have started quality inspections.

    The case is the latest in a series of food safety problems. Recent cases include parasite-infested snails in Beijing, steroid-tainted pork, and ducks and hens that were fed cancer-causing Sudan dye to make their yolks red.

    Wang Yongqiang, deputy director of the Seawater Fishery Institute in Shandong, told Xinhua there are no strict market access rules for turbot so even fish containing carcinogens are not banned.

    Shandong accounts for 80 percent of turbot production in China. The carcinogen-containing fish found in Shanghai were from the eastern province.

    Wang said that individuals were raising more turbots than enterprises and are more likely to use substandard drugs.

    Due to their low resistance to disease, the fish, introduced by Cao Jilin from Europe in 1992, are sometimes fed large quantities of medicinal supplements, which leave harmful, cancer-causing residues in their flesh.

    The State Food and Drug Administration has ordered local offices and authorities in coastal areas including Shandong, Jiangsu, Hebei, Zhejiang, Fujian, Guangdong, Liaoning, and Tianjinto closely monitor the case.

    An inspection team from the Ministry of Agriculture and the State Food and Drug Administration has investigated fish farms in Weihai, Shandong. However, details will not be released until the tests are completed.