Simultaneous fluid flow and active particle tracking in three dimensions during collective swimming

Hydrodynamic interactions among swimming or flying organisms can lead to complex flow patterns at the group scale. Utilizing brine shrimp (Artemia salina) as a model organism, we investigate the effects of collective movement on the fluid environment within a 20x20x24 cm measurement volume inside a larger 3000-liter tank. By leveraging the positive phototaxis of brine shrimp, we induce synchronized vertical migration. The technique, which uses a single camera and a scanning laser sheet, combines Particle Tracking Velocimetry (PTV) to track swimmers, which are 1 cm in size, and Particle Image Velocimetry (PIV) for flow measurement. This method provides a detailed analysis of the coupling between individual movements and the resulting fluid dynamics. This approach enables further investigation into collective swimming, offering new insights into collective behavior in aquatic and aerial environments.