Body size affects the strength of social interactions and spatial organisation of a schooling fish (Pseudomugil signifer)

TL;DR

This study combines experiments and simulations to analyze how body size influences social interaction strength and spatial organization in schooling fish, using a novel statistical approach to validate a self-propelled particle model.

Contribution

It introduces a new application of Boltzmann inversion to fish interactions and demonstrates a model that captures developmental changes in schooling behavior.

Findings

Larger fish have bigger repulsion zones and stronger attraction.

The model accurately reproduces observed social and spatial behaviors.

Fish alignment increases with body size.

Abstract

While a rich variety of self-propelled particle models propose to explain the collective motion of fish and other animals, rigorous statistical comparison between models and data remains a challenge. Plausible models should be flexible enough to capture changes in the collective behaviour of animal groups at their different developmental stages and group sizes. Here we analyse the statistical properties of schooling fish (Pseudomugil signifer) through a combination of experiments and simulations. We make novel use of a Boltzmann inversion method, usually applied in molecular dynamics, to identify the effective potential of the mean force of fish interactions. Specifically, we show that larger fish have a larger repulsion zone, but stronger attraction, resulting in greater alignment in their collective motion. We model the collective dynamics of schools using a self-propelled particle model, modified to include varying particle speed and a local repulsion rule. We demonstrate that the statistical properties of the fish schools are reproduced by our model, thereby capturing a number of features of the behaviour and development of schooling fish.