Cichlid fish view unfamiliar faces longer, from further distance than familiar faces

The theoretical underpinnings of sociality, like territoriality, hierarchy, and reciprocity, are based on assumptions of individual recognition. While behavioral evidence suggests individual recognition is widespread, research on the cues that animals use to recognize individuals are limited. In two experiments, the authors use digital models to test if facial features are a visual cue used for individual recognition in the social fish, the daffodil cichlid. Eight Focal fish were exposed to digital images showing four different combinations of familiar and unfamiliar faces and body colorations.

Focal fish attended to digital models with unfamiliar faces longer and from a further distance to the model than to models with familiar faces. These results suggest that fish may be able to distinguish individuals accurately using facial color patterns. The authors also observed the fish rapidly (? 0.5 sec) discriminate between familiar and unfamiliar individuals; however, the timing of recognition needs further explicit study to investigate how rapidly fish can discriminate familiar and unfamiliar fish in detail.