fish fight for Homeland Security

San Francisco, Washington and New York are using bluegills - also known as sunfish - to safeguard their public drinking water. A small number of fish are kept in tanks which are constantly filled with water from the municipal supply. The computerised system registers changes in the fishes' vital signs and sends an alert when something is wrong. (BBC)

Attacks on U.S. water systems have become a viable threat since September 11.

New York City's bluegills were put to work recently when the system caught traces of a diesel spill before any of the Department of Environmental Protection's other devices. The bluegills do have limitations however. They cannot reliably detect germs and are no use against other sorts of attacks - the bombing of a water main, or computer hackers attacking the systems that control the flow of water.

They also can't pick up guns or fight in hand-to-hand combat, either.