The mechanosensory lateral line is used to assess opponents and mediate aggressive behaviors during territorial interactions in an African cichlid fish.

Fish must integrate information from multiple sensory systems to mediate adaptive behaviors. Visual, acoustic and chemosensory cues provide contextual information during social interactions, but the role of mechanosensory signals detected by the lateral line system during aggressive behaviors is unknown. The aim of this study was first to characterize the lateral line system of the African cichlid fish Astatotilapia burtoni and second to determine the role of mechanoreception during agonistic interactions. The A. burtoni lateral line system is similar to that of many other cichlid fishes, containing lines of superficial neuromasts on the head, trunk and caudal fin, and narrow canals. Astatotilapia burtoni males defend their territories from other males using aggressive behaviors that we classified as non-contact or contact. By chemically and physically ablating the lateral line system prior to forced territorial interactions, we showed that the lateral line system is necessary for mutual assessment of opponents and the use of non-contact fight behaviors. Our data suggest that the lateral line system facilitates the use of non-contact assessment and fight behaviors as a protective mechanism against physical damage. In addition to a role in prey detection, the diversity of lateral line morphology in cichlids may have also enabled the expansion of their social behavioral repertoire. To our knowledge, this is the first study to implicate the lateral line system as a mode of social communication necessary for assessment during agonistic interactions.