Vendredi 18 septembre 2026 à 11h00 ; salle 357 - IUSTI
Abstract: Collective movements can be observed across species and on various scales: from bacteria to mammals. We are interested in the collective behavior of small fish when confronted with external physical perturbations. When forced to escape through a narrow opening, most animals behave like granular materials and clogging events decrease the efficiency of evacuation. In this emergency exit scenario, we challenged the gregarious behavior of a group of macroscopic aquatic agents, neon fish, by forcing the school to pass through a small opening [Larrieu, Sci. Rep. 2023]. Using a statistical analysis developed for granular material and applied to crowd evacuation, our results clearly show that, unlike human crowds or herds of sheep, no clogging forms at the bottleneck. In a second experiment, we perturbed the schooling behavior of a group of zebrafish by adding an array of obstacles to the observation tank [Ventejou Phys. Rev. E 2024]. We observed a behavioral transition from a polarized group when the density of pillars is low to independent fish aligned with the array of pillars. More recently, we developed a minimal model of a swimmer without body deformation that can reproduce swimmer propulsion for a large range of Reynolds numbers, including the wake of vortices in the inertial regime [Ventéjou Phys. Rev. Lett. 2025].