The relationship between personality and the collective motion of schooling fish

The personalities of schooling fish members are thought to have profound effects on group behavior, indicating that group members must maintain their personality to some extent. However, whether and to what extent personality traits are maintained or sacrificed during schooling has seldom been investigated. Thus, we aimed to verify the possible correlation between an individual's personality traits and its movement characteristics during schooling. We first measured the boldness, exploration, activity and sociability personality traits of pale chubs (Zacco platypus). Then, we randomly divided the individuals into ten groups containing six members and measured their movement characteristics. In factor analysis, boldness and activity variables could be reduced to a single factor, and two variables related to sociability and one variable related to boldness (time spent outside the shelter) could be reduced to a single factor. The correlation between factor scores and collective motion traits showed that proactive pale chubs (with greater boldness and activity) swam with higher polarity with the centroid of the group than did reactive individuals, and individuals with higher sociability were more synchronized with the group centroid in terms of swimming speed. These findings suggest that proactive individuals have a greater alignment tendency and might have an advantage of efficient information transfer, enabling them to gain more synergistic benefits as group members than reactive individuals. The present study, along with information from our recent study, suggests that variation in the personality (especially boldness and sociability) composition of fish groups might be a major cause of variation in group-level behavior.