In-line swimming dynamics revealed by fish interacting with a robotic mechanism

Abstract

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 modelling work has suggested that swimming directly in-line behind an individual may lead to increased efficiency. However, no 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.

In-line swimming dynamics revealed by fish interacting with a robotic mechanism

“…We note that the wavelength (as a fraction of the body length) can be computed from the phase lag, and we report this metric in the supplementary data ( Thandiackal and Lauder, 2022 ).…”

Stability of schooling patterns of a fish pair swimming against a flow

“…Schooling refers to the coordinated swimming of fish in close proximity in crystallized spatial formations, as exhibited by most fish species (Filella, Nadal, Sire, Kanso, & Eloy, 2018;Kalueff et al, 2013;Shaw, 1978). Different patterns of fish schooling that are often shown to emerge include side-by-side (phalanx), in-line and staggered (diamond) formations (Daghooghi and Borazjani, 2015;Hemelrijk et al, 2015;Oza, Ristroph, & Shelley, 2019;Park & Sung, 2018;Thandiackal & Lauder, 2022;Weihs, 1973). One approach to explain schooling is based on the premise of collective energy savings so that fish arrange their positions with respect to their neighbours in an attempt to reduce their swimming costs (Ashraf et al, 2017;Liao, Beal, Lauder, & Triantafyllou, 2003a;Maertens et al, 2017;Marras et al, 2015).…”

“…Towards this aim, we focus on a fish pair as a minimalistic instance of a school. Experimental studies involving pairs of live fish have shown evidence for specific schooling configurations, such as side-byside (Ashraf, Godoy-Diana, Halloy, Collignon, & Thiria, 2016;Chicoli et al, 2014) as well as in-line (Thandiackal & Lauder, 2022) configurations, when swimming against a flow. Recent work by De Bie, Flow E31-3 Manes, and Kemp (2020) has further shown that pairs of fish tend to swim in-line in placid water, side-by-side in a high speed flow, and without any identifiable pattern in a low-speed flow.…”