Police officers jump to the deck of a fishing vessel that they said illegally took knife fish in Shanghai on March 28, 2016.[Photo by Yin Liqin/China Daily]

A regulation in the pipeline that would ban fishing for knife fish in the Yangtze River has created an unprecedented surge of interest in Shanghai to eat what could be the last bite of the river delicacy, pushing the price up of the already expensive fish.

One veteran restaurant worker said she had never seen so much interest in the fish.

"I have been working here since I graduated from middle school more than 40 years ago, and we have never had so many customers," said the woman, a cashier at the Lao Ban Zhai restaurant who gave her surname as Liu.

The historic eatery, which was founded in 1904, has long been famous for its steamed knife fish and knife fish with noodle soup in Shanghai and beyond. In the past, it was rarely packed and appealed mainly to local seniors and die-hard fans of its fish dishes, but that all changed two weeks ago.

The number of bowls of fish soup noodle being sold "has been picking up every day, especially since this week", Liu told China Daily on Tuesday, adding that the restaurant sold more than 1,100 bowls during dinner.

Late in December, the Ministry of Agriculture issued a document soliciting public opinion on listing knife fish and shad in the Yangtze as protected species. If the change is passed, this year could be the last that people will legally be able to eat the fish, which is considered to be one of the top four delicacies from the river.

Eating knife fish during the spring season is widely considered as much a tradition as consuming hairy crabs in autumn among people on the lower reaches of the river. Knife fish caught after the Qingming Festival, or Tomb Sweeping Day holiday, which falls on April 4 or 5, are deemed particularly special because the bones will be less hard and the flesh less fatty.

"It's like a routine that, after the festival, the price would jump by 50 percent," said an administrator surnamed Zhu at Tongchuan Road fish market in Shanghai, the largest of its kind in the city.

There are around 40 stores or counters selling knife fish at the market this year. Knife fish weighing less than 100 grams each sell for around 4,000 yuan ($618) per kilogram. Bigger fish sell for as much as 12,000 yuan per kilo. The prices are double last year's and more than at any time during the past four years.

For traders, the problem at the moment is the unsteady and dwindling supply, which hit record lows this year.

"The priority is always to maintain the supply to restaurants and hotels first," said Han Bin, who has been selling knife fish and other river food at the market for five years.

Wang Shiping, a fisherman from Jiangsu province, told media outlet Wenhui Daily that he had managed to net only two "big knives" (each weighing in at more than 100 grams) during the past week. His catch is about 10 percent of what it was last year, he said. The normal fishing season this year runs from March 1 to April 20.

While fishing bureaus in the Yangtze River Delta have tried to ensure that only licensed fishermen are out on the river, illegal profit-driven fishing boats still take great risks to catch knife fish, which is believed to be a major factor in the reduction of the fish population.