A worker feeds a Chinese sturgeon that is to be returned to nature at Beijing Aquarium on March 22, 2007. [Photo: Xinhua]

Severe pollution in the Yangtze River is threatening the existence of the Chinese sturgeon, or Acipenser sinensis, an anadromous fish that has lived on the earth for more than 140 million years.

Xinhuanet.com reported the only nesting area for the sturgeon, which is along the Yichang section of Yangtze River in central Hubei province, has been seriously contaminated by sewage discharged by local enterprises.

According to an official with the local environmental protection department, more than one million tonnes of industrial waste water was discharged into the river untreated every year, averaging 3,000 tonnes a day.

An official with the Chinese Sturgeon Research Institute said pollution is one of the major factors causing the deaths of the fish, nicknamed a "living fossil" by researchers for its value in biological evolution studies.

The official said the wastewater bears a high content of toxic chemical elements, which continues to deteriorate water quality in the country's longest river.

Harmful toxins such as nitrogen and phosphor can lead to the reduction of oxygen in the water and affect the metabolism of or even cause gene mutations in the fish, the official explained.

China established a natural reserve for the sturgeon in 1981 and listed it as a national top-level protected animal in 1988. However, the headcount of the fish continued to decrease due to worsening ecology.

Documents from the Water Resources Protection Bureau in Yangtze River Basin show that the 650-kilometer waterway between the sturgeon's home and the river's mouth is polluted.

A chief researcher from the Chinese Sturgeon Research Institute, Liu Denghong, said more than 3,500 sturgeons would return to the reserve for spawn every year before 1981, but the number has been less than 500 in recent years.

According to a report released by the World Conservation Monitoring Centre, the number of wild Chinese sturgeon is still declining at present and the fish would disappear in 10 years unless effective measures are taken.

Liu said the institute must capture some wild sturgeons every year for artificial propagation, a measure approved by the Ministry of Agriculture to avoid the extinction of the animal.

However, the situation is not turning for the better, Liu said. The pollutants have impacted fecundity and cause a significant gender imbalance among sturgeons. The fish's gonads have degenerated and their sperm, which used to last up to 30 minutes in the past, is now only able to maintain a lifespan of less than five minutes.

The Chinese sturgeon is not the only animal extinction threat in the Yangtze River. Another ancient animal in the river, the white dolphin, was announced close to extinction after an international research team failed to find any in their 38-day search tour in 2006 stretching 3,336 kilometers on the river.

Experts have suggested the government take more strict measures, including enacting special laws to protect the river and avoid a replay of the dolphin tragedy.