Back in the 1970s my father was the Principal Scientist for Anglian Water. He had a tank made with perspex sides and three compartments. A fish was placed in each compartment and cameras and light sensors front and behind. The fish could only swim forward against the constant flow of water taken from the river intake. This way they had a real-time indicator of river water quality.,(reply>), Heigham  :) I met the guy that created the Icons for the fish on the monitoring application, in the 1990's