SHOALING ENHANCES CADMIUM AVOIDANCE BY LAKE WHITEFISH, COREGONUS-CLUPEAFORMIS

We compared the behavioural responses of solitary and shoaling lake wh itefish, Coregomus clupeaformis, to Cd solutions, testing the hypothes is that fish are more responsive to contaminant gradients when in a sh oal than when alone. The movements of individual fish were tracked in a countercurrent-type trough with clean water on one side, and water c ontaining sequentially increasing Cd concentrations (0.2-125 mu g 1(-1 )) on the other; the tracked fish was either alone, or within a shoal of four fish. We quantified a number of parameters derived from elemen ts of locomotor behaviour and spatial selection (including the percent -time spent on the Cd-treated side) as potential indicators of respons e. Individuals in shoals responded to Cd more strongly and at lower co ncentrations than did solitary fish. While this was indicated by stron ger avoidance of Cd, other response measures associated with escape be haviour illustrated this difference more clearly. Our results suggest that the social influence of shoaling enhances a fish's ability to res pond to the presence of contaminants.