Abstract
A rapid automatic biological monitoring system, intended to complement physical-chemical monitoring techniques, has been developed which utilizes the fact that fish opercular rhythms increase under toxic conditions. Any increase which is above the rate to be expected under normal conditions is monitored electronically. An in-built visual alarm system serves as an advance warning of the development of a critical toxic condition. The system also has the ability of controlling toxic industrial discharges, thus aiding the preservation of the quality of receiving waters.