TY - JOUR TI - In-line swimming dynamics revealed by fish interacting with a robotic mechanism AU - Thandiackal, Robin AU - Lauder, George A2 - Lentink, David A2 - Rutz, Christian A2 - Porfiri, Maurizio VL - 12 PY - 2023 DA - 2023/02/06 SP - e81392 C1 - eLife 2023;12:e81392 DO - 10.7554/eLife.81392 UR - https://doi.org/10.7554/eLife.81392 AB - Schooling in fish is linked to a number of factors such as increased foraging success, predator avoidance, and social interactions. In addition, a prevailing hypothesis is that swimming in groups provides energetic benefits through hydrodynamic interactions. Thrust wakes are frequently occurring flow structures in fish schools as they are shed behind swimming fish. Despite increased flow speeds in these wakes, recent modeling work has suggested that swimming directly in-line behind an individual may lead to increased efficiency. However, only limited data are available on live fish interacting with thrust wakes. Here we designed a controlled experiment in which brook trout, Salvelinus fontinalis, interact with thrust wakes generated by a robotic mechanism that produces a fish-like wake. We show that trout swim in thrust wakes, reduce their tail-beat frequencies, and synchronize with the robotic flapping mechanism. Our flow and pressure field analysis revealed that the trout are interacting with oncoming vortices and that they exhibit reduced pressure drag at the head compared to swimming in isolation. Together, these experiments suggest that trout swim energetically more efficiently in thrust wakes and support the hypothesis that swimming in the wake of one another is an advantageous strategy to save energy in a school. KW - fish schooling KW - robotics KW - in-line swimming KW - thrust wakes KW - fluid dynamics JF - eLife SN - 2050-084X PB - eLife Sciences Publications, Ltd ER -