A photoelectrochemical method for tracking the motion of Daphnia magna in water.

We present the novel use of photoelectrochemistry to detect and monitor the motion of a single Daphnia magna swimming in a confined volume of water. Using an array of individually-addressable electrodes under illumination and potentiostatted so that a photocurrent is generated, the motion of the daphnid is detected by means of measuring "dark" transients as the shadow cast by the moving sphere passes over each electrode. The method can be used to determine the size and speed of a single daphnid.