Winners and Losers: social modulation of behaviour in zebrafish (Danio rerio)

In nature animals fight to acquire or defend vital resources such as food, shelter or access to mates. Aggressive behaviour is a quantifiable response to social stress, which is intrinsic to an individual and prevalent throughout the animal kingdom. In dyadic agonistic encounters, behaviour can be characterized by several specific behavioural patterns, usually dependent on the actions of the opponent. It was already shown that fighting behaviour is influenced by prior experiences, which is reflected in the outcome in later contests. The winner in a first combat is more likely to dominate during a second encounter, whereas a loser in a first contest has more probability to lose again in later contests. Zebra-fish (Danio rerio) is a model system extensively used in genetic, developmental biology, neurophysiology and biomedicine studies. This fish exhibit distinct patterns of aggressive behaviour and establishes hierarchies of dominance-subordinance. The aim of this study was to identify behaviours of this social species during agonistic encounters. Subsequently we characterized this dominance-subordinance behavioural pattern between pairs of male zebrafish and analysed the influence of prior experiences in later agonistic encounters. Our results showed that the probability of a loser to lose an interaction is higher than the probability of a winner to win a subsequent fight which confirms that both winner and loser effects are present in zebrafish. We showed for the first time that one single social encounter is enough to induce long-lasting behavioural changes in losers and transient changes in winners of zebrafish males.