Mechanical Properties of Fish Shoals

Schooling fish stay as a cohesive unit despite each individual consuming energy and moving on its own. This collective can be considered an amorphous soft material that both influences and is influenced by its individual components, but still retains quantifiable physical properties. We investigate these properties of soft active materials by finding the mechanics and structure of fish shoals in an experimental laboratory setting. We use imaging and image analysis techniques to extract the positions and trajectories of individual fish within groups confined to a quasi 2D volume of water. In order to find how individuals take up space within a shoal and interact with their neighbors we apply a Voronoi tessellation to the fish positions, which defines an effective unit cell for our amorphous material. This allows us to measure how changing the shoal's confinement geometry and population affect individual fish and the shoal as a whole.