A sample inspection of crayfish produced in East China's Jiangsu province shows they are 100 percent safe, local supervision and testing authorities have said.

It was the first official inspection after the media reported on Aug 23 that more than 10 people in Nanjing, capital of the province, had been diagnosed with muscle degeneration after eating crayfish contaminated with an excessive residue of chemical detergent.

Market administrators in Lianyungang city, Jiangsu province, inspect the cooked crayfish in a local restaurant on Aug 25. [China Daily]

"After the incident, we worked with Jiangsu Aquatic Products Analysis and Testing Center and Nanjing Aquatic Products Quality Testing Center under the Ministry of Agriculture to conduct an immediate province-wide sample inspection," Shen Yi, deputy director of Jiangsu Oceanic and Fishery Administration, said on Saturday.

Shen said the inspection consisted of three samples of feed and 35 crayfish, including 13 from ponds and 22 from wholesale markets.

"Our sample inspection showed the crayfish is 100 percent of good quality," Shen was quoted by the Yangtse Evening News as saying.

China exports crayfish, or crawfish, predominantly to the European Union and the United States, with $160 million worth of crayfish exported in 2009.

Crayfish from Jiangsu province has an increasing share of the export market. From January to July this year, Jiangsu province exported 1,187 tons of intact crayfish and 1,842 tons of shelled crayfish, increases of 24.4 percent and 11.7 percent over the preceding year, according to the Jiangsu Oceanic and Fishery Administration.

Agricultural products imported into Europe and the US must meet stringent safety requirements, so crayfish exported to those two markets is definitely certified for quality, Shen said.

Following the recent incident in Nanjing, many netizens expressed the opinion that crayfish is inedible, while some said crayfish is used to purify sewers in Japan.

"People used to say that the dirtier the water is, the fatter the crayfish will be. That is not true," Shen said.

"It is important to have a good environment for raising crayfish. In our experience, crayfish thrive in clean water, which helps fatten them up for the market."

Nevertheless, the unbearable muscular pains experienced by the Nanjing residents who apparently ate tainted crayfish remains unaccounted for.

Doctors speculated that the powder used to wash shrimp, a detergent that contains oxalic acid, could be responsible for the incident.

Excessive residual levels of the detergent caused the residents to develop rhabdomyolysis, a deterioration in muscle fiber, which can cause kidney failure or death after it is released into the bloodstream, Xinhua News Agency reported.

The "shrimp washing powder" is popularly used by many sellers to make the crayfish or shrimp look fresh and clean, according to local media reports.

The safety inspection was conducted according to standards employed by the Ministry of Agriculture, according to Fei Zhiliang, an official of the Jiangsu Oceanic and Fishery Administration.

The crayfish sample was sent to the National Center for Disease Prevention and Control for further investigation.

(China Daily September 6, 2010)