Morphology as a key to behavioural flexibility: body shape and swimming variability in the dimorphic crucian carp

Abstract. Swimming trajectories of length-matched deep-bodied and shallow-bodied crucian carp were quantified in the laboratory using motion analysis software and compared in terms of swimming velocity, turning behaviour and associated coefficients of variation. The mean velocities of the two morphs were similar, but slower than predicted, and there was no difference in turning behaviour. In line with predictions from analysis of power curve steepness, swimming velocities of deep-bodied, high-drag individuals were significantly less variable than shallow-bodied conspecifics, thus indicating an association between body shape behavioural flexibility in terms of swimming variability.