In 1990 I worked for a company called Biological Monitoring Inc that made a product called the "Biocell," a small aquarium that housed a single fish and monitored its gill voltage to detect a respiratory pause when pollutants were introduced to the water. I have no idea if this is where they got the idea or if it ever went anywhere.,(reply>), I remember having seen something similar to this, but with fish as a sensor, years ago, so - the basic idea seems to be alive and well, only maybe a little less invasive (?) than gill voltage: I think the movements of the fish are detected by camera, in clean water the fish are using all water volume, and with toxins they keep more to the ground, or something along those lines...