Fish focus primarily on the faces of other fish

"Face" is a special stimulus in humans and, nonhuman primates, and some other social mammals; that is, they perceive the face differently from the other body parts and other stimuli. In these species, the face conveys much information, so individuals examine the face at first sight rather than other body parts. Similar to mammals, the faces of fish also convey much information, but little is known about whether fish pay attention to the face or face-viewing patterns. Here we document the face-viewing patterns of the cichlid fish Neolamprologus brichardi, which can distinguish between conspecifics based on facial colouration. First, we established a method to identify the point at which subject fish inspected. Fish often fixated in direction to their heads toward the object of attention, suggesting that the extended body axis indicated the attention point. Using this attribute, we examined the point of attention of subject fish presented with photographs of conspecifics and heterospecifics. The results revealed that the fish inspected initially and repeatedly at the face and the duration was longer for the face than other body parts.