Individual leadership and boldness in shoals of golden shiners (Notemigonus crysoleucas)

Shoals of golden shiners (Notemigonus crysoleucas) often swim along the perimeter of their large indoor tank at dawn and dusk, and can also be trained to anticipate food arrival by swimming directly towards the food source at midday. In this study all golden shiners in six shoals of 8-12 fish were individually marked with a visible implant elastomer, and shoal movement was video taped in order to determine whether some individuals consistently occupied front positions even when all shoal members were of similar size and experience. There were significant correlations between all three times of day (dawn, midday, dusk) in the mean position (from 1 = first at the front of the shoal to 12 = last at the back) occupied by each fish. In each shoal, 1-3 fish were leaders: all three daily times combined, they had more than twice the occupancy rate of the front two or three positions as expected from chance. In subsequent boldness tests there was a tendency (p = 0.096) for these leaders to pass through dark U-shaped tubes more readily than non-leaders. However, after being dipnetted and transferred to a refuge, leaders did not emerge earlier than non-leaders. Individual tendencies to lead may have been underlain by a motivation to feed (which may differ even in fish of similar size and experience) or by intrinsic mobility. On the other hand, a link between leadership and risk-taking remains to be established for captive golden shiners.