Chinese scientists have adopted the principle of the coal mine canary to monitoring water quality by using fish to test for pollutants.

A machine containing more than 20 small fish has been used to monitor water quality in Beijing, said Wang Zijian, a professor with the Research Center for Eco-Environment Sciences, of Chinese Academy of Sciences.

"These fish safeguard the sources of the capital's domestic water day and night," said Wang.

The machine, located in the southwest of Beijing contains, eight cuvettes, each holding water sample and three to four fish about two or three centimeters long.

"The behavior of fish will change in case of contamination, such as the speed of their movement," said Wang.

The change is detected by the machine and an alarm is sent to the computer monitor and inspectors' mobile phones.

Only fish highly sensitive to slight pollutants were chosen, said Wang.

"We have thousands of such fish in our breeding tanks," Wang said.

The major breeds included Japanese killifish and zebra fish from India, which were widely adopted by the international counterparts. Fish aged just three or four months were the best suited to the job.

Each batch of fish was replaced every two weeks in order to prevent them adjusting to pollutants, Wang said.

The fish were taken to Chengdu, of southwest China's Sichuan Province, after the devastating earthquake on May 12 last year, to ensure the safety of the city's drinking water sources.

(Xinhua News Agency July 15, 2009)