An Osaka City University research team said Thursday it found that a species of African fish called daffodil cichlid, which lives in large groups, can distinguish unfamiliar faces from familiar ones.
The study was the first to indicate that fish can recognize individuals by looking at their faces.
Previous studies have shown that some animals, such as chimpanzees, can distinguish the facial features of others. It was not known whether fish possessed this ability.
Masanori Koda, a professor at Osaka City University, and his colleagues conducted experiments with the cichlid, a species living in Lake Tanganyika in Africa.
The fish live in large family groups organized by dominance hierarchy. Researchers had already found that the fish were able to recognize fellow group members using only visual cues but had yet to determine the visual signals they used to identify others.
In the latest study, reported online by the U.S. scientific journal PLOS One, the cichlids were exposed to digital images showing four different combinations of familiar and unfamiliar faces and body colorations.
The fish viewed the images of the unfamiliar faces for longer and from further distances than they did with the images of familiar faces, the article said.
The two-part experiments demonstrated that facial features are the visual cue used for individual recognition in the social fish, the group said. The Japanese researchers also said that the results strongly suggest that fish can distinguish individuals accurately using facial color patterns.
The Japan Times Ltd.