Several shots from different angles in a laboratory of the Freshwater Institute of a hand starting up analysis machine, of a woman technician weighing fishes in test tube and adding acid to it, of fishes, of wood snails, leech, freshwater shrimps, stonefly nymphs and crayfish. Various interior shots of Dr Scherer standing by a large tank watching fishes in it, of him at work with specialize equipment, of a paper tape readout, of numbers changing fast on a red voltage readout (as fishes are passing in front of sensor machine in tank) and of the oscilloscope, of a tape readout punching machine. Underwater shots of fishes in tank with fish sensor machine in evidence.