Influence of Body Size on Leadership in Shoals of Golden Shiners, Notemigonus Crysoleucas

Summary In shoals of uniformly-sized golden shiners ( Notemigonus crysoleucas ), a minority of individuals who know when and where food is available can lead their nai ve shoalmates to food. The present study investigated whether such leadership still takes place when leaders and followers are of different body size. Shoals of either 3 small and 9 large shiners, or 3 large and 9 small ones, were trained to expect food around midday in one of the corners of their large tank. The shoals revealed their learning by anticipating food arrival, i.e. by spending an increasing amount of time in the food corner up to midday. The 9 similarly-sized shiners were then replaced by 9 others of the same size who had never been in the tank before. When the remaining minority of knowledgeable e sh were the large individuals, the new small e sh followed them to the food corner the next day. These large leaders occupied front positions, though a few days earlier when the whole shoal had been experienced they had tended to stay at the back of the shoal as it entered the food corner. When the remaining minority of knowledgeable e sh were the small individuals, the new large e sh refused to follow them on at least half of the six trials. Knowledgeable small e sh tended to be at the front of the shoal, either when the whole shoal was experienced or on the few occasions when nai ve large e sh accepted to follow them. The behaviour of the large e sh suggests that they were motivated primarily by wariness, whereas that of the small e sh is more compatible with a motivation to e nd food. Reluctance by large e sh to follow small ones may contribute to the body size assortativeness of e sh shoals in the wild.