Behavioural laterality in the shrimp-eating cichlid fish Neolamprologus fasciatus in Lake Tanganyika

Behavioural laterality has been observed in various vertebrates, including fish, but its significance is little known. This study investigated behavioural laterality, corresponding to morphological asymmetry, in individuals of the cichlid Neolamprologus fasciatus as they hunted shrimp. This species shows lateralized hunting; when aiming at prey, individuals bend with either the left or the right side of the body abutting a rock. In field observations, the numbers of leftward and rightward hunts were recorded during 1-h periods for each of 44 individuals. The frequency distribution of the proportion of rightward hunting was bimodal, and approximately one-third of the observed individuals showed a significant leftward or rightward bias. The degree of behavioural laterality of each fish was associated with that of morphological asymmetry of the mouth but not with any of four bilateral characters (outer teeth in upper jaw, gill rakers, upper lateral line scales and lower lateral line scales); ‘lefties’ (‘righties’) showed more rightward (leftward) hunting. Furthermore, it was suggested that hunts corresponding to each individual's mouth laterality achieved higher hunting success than did reverse hunts. Antisymmetrical hunting behaviour in a population may affect predation efficiency on the basis of frequency-dependent selection.