Local fishery officials of Shanghai Municipality yesterday warned people to avoid seafood as much as possible as a large, toxic red tide is developing off the coast of neighboring Zhejiang Province.

Fishery experts took samples at several major aquatic wholesale markets yesterday to see if polluted seafood has entered the city.

"Despite the measures, people had better not eat too much seafood these days because it is hard for the sample test to cover all the market supply," said Meng Yaorong, of the Shanghai Fishery Office, adding that a great deal of the seafood sold in local markets, except for shrimps, comes from Zhejiang Province.

Meng admitted, however, it is very hard for inspectors to say with any certainty where most seafood comes from.

"The fishing area where seafood is caught is viewed as a commercial secret by fishermen and they won't tell us the truth," said Yang Jihua, manager of the Tongchuan Road Aquatic Products Wholesale Market, the largest of its kind in the city.

As a result, officials remind people to be careful especially when buying shellfish and crabs.

Yang said market managers are waiting to hear test results and will take measures as required by the city government if any problem is found.

The State Environmental Protection Administration reported on Friday that a large red tide has occurred in the East China Sea near the Zhoushan Islands of Zhejiang Province.

So far, the red tide has covered 20,000 square kilometers, and there is no evidence to suggest it will fade away any time soon. Toxic algae have also been uncovered.

The red tide, bringing about reddish discoloration of coastal ocean waters, is caused by an increase in bacteria and algae. If the algae contain toxins, it will accumulate within fish and shellfish, making them poisonous to eat.

"The red tide situation is becoming more serious in recent years with the increasing pollution caused by industrial development," Meng said. "Such large red tides have rarely been recorded."

Officials with the East China Sea branch of the State Oceanic Administration said that red tides reach their peak in the East China Sea in May and June.

"Whether a larger red tide will break out still depends on the temperature, wind force and the water temperature," said Wu Zhennan, deputy director of the environmental protection division under the East China branch. "It is extremely difficult to predict because the natural conditions are always changing."

He said the red tide is also expected to appear on the sea water near Shanghai. Red tides were reported 10 times last year in areas near the city. The largest one covered 1,000 square kilometers.

(Shanghai Daily May 18, 2004)