The warning comes after a farmer named Xiao Chunsheng, from central China's Hubei Province, caught a strange fish in the Hanjiang River, a tributary of the Yangtze, as he was swimming in the river on Saturday morning.

The fish was described as having flowing black stripes down the length of its body, with the mouth bigger on the lower side of its head, and with a flat belly and narrow back.

On examining the fish, Professor Chen Wei, of the Aquatic Life Institute of the Chinese Academy of Sciences, concluded it was a kind of catfish from the Amazon River in South America.

Professor Chen ruled out the possibility that the fish had swum across the ocean, up the Yangtze to the Hanjiang River.

"It is certain that the fish was brought into China as an ornamental fish, but was released into the Hanjiang River later," the expert was quoted as saying by Beijing Youth Daily yesterday.

"Releasing foreign aquatic species into China's rivers at random may easily lead to an invasion of foreign species into China's biosphere," said Chen, who feared that the foreign fish could cause disastrous damage to the country's ecological balance if it propagated and formed a new species in Chinese rivers.

China already suffers from the hyacinth, a water-based plant which used to be found only in South America, and has to spend huge sums every year to remove the plant from rivers.

The plant was introduced to China 50 years ago as fodder for pigs. Uncontrolled growth of the plant leads to pollution of the water and stifles the growth of aquatic life. The hyacinth has been listed as one of the world's 10 most harmful plants.

(Xinhua News Agency July 30, 2002)