BEIJING, Sept. 19 (Xinhuanet) -- One of the most common types of fish inU.S. has been enlisted in the fight against terrorism. Big cities including San Francisco, New York, Washington are using bluegills, also known as sunfish or bream, to safeguard their drinking water.

Small numbers of the fish are kept in tanks constantly replenished with water from the municipal supply, and sensors in each tank work around the clock to register changes in the breathing, heartbeat and swimming patterns of the bluegills that occur in the presence of toxins.

"Nature's given us pretty much the most powerful and reliable early warning center out there," said Bill Lawler, co-founder of Intelligent Automation Corporation, a Southern California company that makes and sells the bluegill monitoring system. "There's no known manmade sensor that can do the same job as the bluegill."

Since Sept. 11, the government has taken very seriously the threat of attacks on the U.S. water supply. Federal law requires nearly all community water systems to assess their vulnerability to terrorism.

Big cities employ a range of safeguards against chemical and biological agents, constantly monitoring, testing and treating the water. But electronic protection systems can trace only the toxins they are programmed to detect, Lawler said.

Bluegills, a hardy species about the size of a human hand, are considered more versatile. They are highly attuned to chemical disturbances in their environment and when exposed to toxins they experience the fish version of coughing, flexing their gills to expel unwanted particles. Enditem