Behavioural syndromes and shoaling: Connections between aggression, boldness and social behaviour in three different Danios

While many behavioural syndrome studies focus on individual-level correlations of behaviors across various contexts, it is also possible to examine these syndromes on a population level, comparing various species or groups. In this study we tested wild type zebrafish (Danio rerio), longfin zebrafish (Danio rerio lof mutants) and the closely related pearl danio (Danio albolineatus) to determine whether aggression and boldness varied and whether population-level differences in these behavioural types were linked to differences in shoaling preferences among the three Danio types. We found significant differences in overall levels of boldness and aggression between the three Danio groups. Pearl danios were the most 'aggressive' type, and wildtype zebrafish were relatively 'passive'. In contrast, wildtype zebrafish showed the most 'boldness' while longfin zebrafish were comparatively 'shy'. We also found subsequent differences in social behaviour, with pearl danios showing significant preferences for conspecific shoals. Our results indicate that fish may not only be making social decisions based on the behaviour, health and appearance of potential shoal mates, but their own temperament may be important in mediating social interactions as well.