Collective orientation of an immobile fish school, effect on rheotaxis

Renaud Larrieu , Catherine Quilliet , Aurélie Dupont (1) , Philippe Peyla

1 LIPhy - Laboratoire Interdisciplinaire de Physique [Saint Martin d’Hères]

We study the orientational order of an immobile fish school. Starting from the second Newton's law, we show that the inertial dynamics of orientations is ruled by an Ornstein-Uhlenbeck process. This process describes the dynamics of alignment between neighboring fish in a shoal, a dynamics already used in the literature for mobile fish schools. Firstly, in a fluid at rest, we calculate the global polarization (i.e. the mean orientation of the fish) which decreases rapidly as a function of the noise. We show that the faster a fish is able to reorient itself, the more the school can afford to reorder itself for important noise values. Secondly, in the prescence of a stream, each fish tends to orient itself and swims against the flow: the so-called rheotaxis. So even in the presence of a flow, it results in an immobile fish school. By adding an individual rheotaxis effect to alignment interaction between fish, we show that in a noisy environment, individual rheotaxis is enhanced by alignment interactions between fish.

Domaines: Biophysique [physics.bio-ph]

Renaud Larrieu, Catherine Quilliet, Aurélie Dupont, Philippe Peyla. Collective orientation of an immobile fish school, effect on rheotaxis. 2020. ⟨hal-03040231⟩