A high-tech ichthyological version of a canary-in-the-coal-mine warning system is nearing market. It's a system that monitors fish behavior as an early general warning of water purity problems. The system is being tested in several places, including New York City's reservoir system, ahead of commercialization later this year.

The system, developed at the U.S. Army Center for Environmental Health Research at Fort Detrick, MD, uses bluegill fish to detect a broad range of toxic chemicals. It doesn't look for anything specific; it detects anything that would stress a fish, from chlorine to cyanide. Each fish serves two-week tours of duty inside a plastic chamber containing two electrodes. The electrodes sense electrical signals from the fish's muscle movements. During an initial calibration period, software learns an individual fish's normal breathing rate and depth, gill movements, and overall body activity. During water monitoring, software detects departures from normal measurements, which can indicate the fish is stressed.