A study by the University of Queensland in Australia has found that the ambon damselfish (Pomacentrus amboinensis) have unique facial patterns that can only be seen under ultraviolet light and these patterns can be seen by their fellow ambon damselfish because they can see UV wavelengths. This enables the fish to identify each other without drawing attention to predators, which can’t see the UV light.
Mature Ambon damselfish without eyespot. Photo by Wikipedia
Researchers Ulrike E Siebeck , Amira N Parker, Matthias O Franz, and Guy M Wallis conducted associative learning experiments on the damselfish, giving them food rewards when they were able to discriminate between fishes as well as fish species and found that the fish were able to differentiate between printed images of a fish’s face or on a computer screen, of head and facial markings of fish.
The fish quickly learned to distinguish between two facial patterns from conspecific or heterospecific fishes. They learned the subject fish were highly sensitive to slight pattern differences in the fish they had to identify and that there was a 75 percent accuracy in classifying the faces.
They determined that the fish were able to recognize faces even though fish lack a neocortex.