# Noise-Induced Schooling of Fish

## TL;DR

This study shows that collective schooling in fish is driven by intrinsic noise, with fewer fish increasing the likelihood of alignment, challenging traditional models of collective behavior.

## Contribution

It provides empirical evidence that noise induces schooling in fish and constrains the underlying interaction mechanisms, highlighting the fundamental role of stochasticity in collective motion.

## Key findings

- Schooling is noise-induced and more likely with fewer fish.
- Fish align one at a time, not by local averaging.
- Noise is essential to understanding collective behaviors.

## Abstract

We report on the dynamics of collective alignment in groups of the cichlid fish, Etroplus suratensis. Focusing on small-to-intermediate sized groups ($10<N<100$), we demonstrate that schooling (highly polarised and coherent motion) is noise-induced, arising from the intrinsic stochasticity associated with finite numbers of interacting fish. The fewer the fish, the greater the (multiplicative) noise and therefore the likelihood of alignment. Such empirical evidence is rare, and tightly constrains the possible underlying interactions between fish: computer simulations indicate that E. suratensis align with each other one at a time, which is at odds with the canonical mechanism of collective alignment, local direction-averaging. More broadly, our results confirm that, rather than simply obscuring otherwise deterministic dynamics, noise is fundamental to the characterisation of emergent collective behaviours, suggesting a need to re-appraise aspects of both collective motion and behavioural inference.