Laser guidance system for induction and control of vertical migrations of plankton aggregations. (a) The setup consists of a 447 nm laser (1) that generates a horizontal blue laser beam (2), which is aligned with a vertical green laser sheet (3), generated by a 532 nm laser (4), and a −25 mm focal length cylindrical lens (5), and introduced from above the tank. A vertical, red laser sheet (6) is introduced from the side of the tank and is produced using a 635 nm laser (7) and a −3.9 mm focal length cylindrical lens (8). PIV measurements are recorded within the overlap region (9). (b) Photo of the setup during a migration event, after the 447 nm laser has completed its vertical traverse of the tank. The image was captured at an angle, producing duplicate reflections of the lasers in the two visible sides of the tank. See the corresponding video of the experiment. (Multimedia view). [URL: http://dx.doi.org/10.1063/1.4895655.1]