Title: Abstracts from the 35th Annual Meeting of The Japanese Society for Comparative Physiology and Biochemistry
Abstract: Recent theories (e.g.social intelligence hypothesis) predict that selection favors enhanced social cognitive ability such as individual recognition in animals living in higher sociality.Social vertebrates recognize group members often optically, but less studied is with which visual cues and how animals use the cue for individual recognition except for some animals, e.g.apes, monkeys and sheep that can do facial recognition.Recent studies indicate that many fish species with high sociality (e.g.stable group and stable territorial neighbor) can recognize individual group members optically.Here we show for the first time the visual cue for individual recognition in fish: the cooperative breeding cichlid Neolamprologus brichardi uses facial coloration for individual identification.This fish distinguished familiar neighbors and unfamiliar strangers, and responded more aggressively against the latter (i.e.dear enemy effect).To test the facial recognition hypothesis, four types of digital fish-model, moving on a monitor display according to the same program, were exhibited to subject fish randomly: (1) neighbor, (2) neighbor face on stranger body, (3) stranger and (4) stranger face on neighbor body.The study fish were less aggressive against models (1) and ( 2), but were highly aggressive toward models (3) and ( 4), strongly supporting the hypothesis that this fish use facial coloration for individual recognition.Our comparative study suggests that this type of facial recognition is likely to develop in group-living cichlids but rarely in non-group living fish such as monogamous pair or schooling fish, implying that not only this species but other cichlids with highly complex sociality also use facial recognition.We further confirm that this fish may discriminate the facial pattern at a glance, which would be comparable to human face recognition by means of face-neuron.We hypothesize that this fish can learn its species-specific facial color pattern easier or faster than different color patterns of similar complexity, and we assume that fish facial-recognition ability will be through special neuron-system comparable to that of human face-neuron located in the right hemisphere.