A number of North American cities are using common bluegills, fish particularly sensitive to chemicals in their environment, to monitor the quality of drinking water. An Associated Press report explains: “The fish are kept in tanks constantly replenished with water from the municipal supply, and sensors work around the clock to register changes in the breathing, heartbeat and swimming patterns of the bluegills that occur in the presence of toxins.” In one instance in New York City, says the report, “the fish noticed a diesel spill two hours earlier than any . . . other detection devices,” and they thus prevented toxins from reaching the public water supply.

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Hundreds of spawning salmon are being tracked by radio receivers along the Columbia River. They were pulled out of the water and a three-inch-long plastic capsule containing a miniaturized, battery-powered transmitter was put down the throat of each. After being put back into the water they are tracked by radio receivers. Each transmitter gives out its own beep code. By means of the transmitters scientists determine the navigational routes of the spawning fish.

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