On the emergence of winner and loser in zebrafish fights*

To resolve disputes, compete for resources, and establish social hierarchies, many animals engage in pair-wise aggressive interactions known as fights. Fights represent a sequence of stereotyped dynamics that lead to the establishment of a winner and a loser. We present work quantifying the emergence of a winner and loser in adult male zebrafish fights. We track multiple body points in 3D and identify a low-dimensional set of state variables for the relative positions and orientations of the fish. We cluster the temporal transitions in this state space to create a symbolic dynamics of short (~1 sec) multi-animal behavioral motifs. As the fight evolves, an asymmetry between the fish develops. The distribution of relative orientations is initially symmetric when the fight begins, but becomes asymmetric as the winner establishes an advantageous position behind the loser for many minutes. To probe the emergence of a winner and loser, we study the progression of this asymmetry and the dynamical features that ultimately lead to an end of the fight.