Image copyright AFP Image caption Chinese scientists released artificially-bred sturgeons into the Yangtze river in April

The Chinese sturgeon, thought to have existed for more than 140 million years, is now on the brink of extinction, according to local media.

Xinhua reported that no wild sturgeon reproduced naturally last year in the Yangtze river.

It was the first time since researchers began recording levels 32 years ago.

Chinese researches say the fall is due to rising levels of pollution in the Yangtze river and the construction of dozens of dams.

Researchers from the Chinese Academy of Fishery Sciences also found that no young sturgeons were found swimming along the Yangtze toward the sea during the period they usually do so.

A researcher told Xinhua that in the 1980s, at least several thousand sturgeon could be found in the river. It is estimated only around 100 fish remain.

"Without natural reproduction, the fish population cannot replenish itself. If there are no further steps taken to strengthen conservation, the wild sturgeon faces the danger of extinction," he said.

Image copyright AFP Image caption Several sturgeon fish are housed in the Beijing aquarium

Image copyright AFP Image caption The finless porpoise, another native species to the Yangtze river, is said to be at risk as well

In recent decades the Chinese authorities have built numerous dams along the 6,300km-long Yangtze river to boost the country's electricity supply. Such moves have drawn criticism of environmental degradation and displacement of villagers.

The WWF says that one of two species of dolphins native to the Yangtze river, the Baiji dolphin, went extinct in 2006 because of declining fish stocks.

The other species, the finless porpoise, is said to be at risk from illegal and intensive fishing practices and pollution. About 1,200 to 1,800 finless porpoises remain in the entire 1.8 million sq km Yangtze basin.