THE arrival of autumn means the time has come for Shanghainese to eat hairy crab a seasonal dish in the city, much the same way turkey is for Westerners.

"It is really difficult to find a good hairy crab," said a local resident surnamed He, who was planning a feast at home for guests during the National Day holiday. "In the market, almost every stall-keeper says their crabs come from Yangcheng Lake. But I know that is impossible."

This year, to avoid fake and low-quality hairy crabs, the Suzhou Yangchenghu Hairy Crab Association prepared 6 million special "rings" as anti-faking marks to be attached to each genuine Yangcheng Lake crab.

The lake located in Jiangsu Province, is the most highly regarded source of tasty hairy crab, and crabs from the lake fetch a much better price than those from other places.

This year, the lake is expected to yield about 1,100 tons of hairy crab, or about 6 million crabs, according to the association's statistics.

In Shanghai's Tongchuan Lu Aquatic Market, some crabs can already be spotted with "rings" on their legs. Engraved on the "ring" is the name of the sales company, with telephone numbers marked on the side for anyone who wants to check the information. On the hidden inner surface of the ring is an 18-digit code - the individual ID number of each crab. Consumers can check the number through the SMS service on their mobile phone to find out if the crab's code really corresponds to an animal from Yangcheng Lake.

"I think this is a very useful step," said Zhang Yunlong, a crab seller in the market. Zhang was unable to hide his smile at being one of the few storekeepers in the market selling merchandise bearing the new rings.

Though he didn't understand how to check the code through SMS, he believed the new measure would add to his commercial prospects.

"I can't tell you how much I make on each hairy crab, but I have huge demand from customers now, not only local restaurants but those as far away as Xinjiang and Henan Province," said Zhang, who has 25 years of experience selling aquatic products.

But some of the other storekeepers in the market doubted whether the new rings would have much effect. They worried the rings themselves would soon be faked.

Last year, the association introduced a laser-marked anti-faking symbol, which was printed on the back of each crab. Quite soon afterwards, fake marks were found everywhere.

"Who cares if they are real Yangchenghu crabs or not? What people care about is whether the crab is large enough, fresh and of good quality. The Yangcheng Lake crab is always more expensive," said one storekeeper, who was unwilling to give his name.

The association has released typical purchase prices for Yangcheng Lake hairy crabs this year. The expected selling price of a 150-gram female crab or a 200-gram male crab is 224 yuan (US$27) per kilogram. For crabs 50 grams larger, the price should be 360 yuan (US$44) per kilogram.

The prices are a little higher than they were last year due to the increased cost of feedstuff and of improved aquaculture technology.