Complex software then analyzes the fishes' actions in reference to tank conditions such as temperature, acidity, and dissolved oxygen levels.
When an abnormality is detected in at least six of the fish, the computer calls or emails the technician on duty.
"It gets a human involved right away," said Bill Lawler of Intelligent Automation Corporation (IAC) in Poway, California.
The private company developed the system's software and sells the unit at a starting price of $45,000 (U.S.).
IAC says there's no humanmade sensor available that can measure toxicity harmful to humans in the same manner as bluegills.
The fish were chosen because of their commercial availability and an established database on their response to toxins.
To keep the fish from being stressed or sick, they "work" for two weeks. Then the bluegills get a break and are fed brine shrimp to keep them "happy."
Lawler says bluegills are highly attuned to water quality changes.
During routine cleanings in the New York City and San Francisco reservoirs, the fish caused an alert after divers kicked up sediment about 40 miles (64 kilometers) away, he says.
And in New York City bluegills detected a diesel leak before it got out of control.
"There's a lot of emphasis on their ability to deter terrorism, but they are also doing a lot in terms of potential watershed monitoring and accidental chemical spills in source water," Lawler said.
Under a pilot project with the U.S. Army, bluegills have monitored New York City's drinking water since 2002.
The biomonitoring unit is currently on loan from the government, but plans are underway to purchase and expand the system, says Ian Michaels, a spokesperson for the New York City Department of Environmental Protection, which supplies water to nine million people.
"We considered it to be worth investigating as an additional layer of security," Michaels said, adding that other tests—literally tens of thousands every year—are also performed to ensure safe drinking water.
Just One More Tool
The push for aquatic biomonitoring first took place in Europe about 20 years ago after a major chemical spill in Switzerland, according to Shedd, the Army biologist.
In addition to fish, other aquatic creatures such as clams and daphnia are used as indicators of chemical changes (see fish photos, profiles, and more).
"It's just recent that the U.S. has become interested in this capability," Shedd said.
"It's one tool in an arsenal of tools to monitor for water quality and to protect surface waters," he added.
"It's not a stand-alone technology. It's a complement to the current technology we already have out there."
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