A fish that knows you
In the mangrove estuaries of Southeast Asia and Australia lives a fish with a remarkable skill. The banded archerfish, Toxotes jaculator, is famous for its ability to shoot jets of water with incredible precision to knock insects and other small prey off overhanging branches. This hunting method requires the fish to account for the refraction of light between water and air. But its visual talents do not end there. Research shows this fish can be trained to recognize and remember individual human faces.
A 2016 study published in Scientific Reports showed this capacity. Researchers from the University of Oxford and the University of Queensland trained archerfish to spit at a specific human face displayed on a computer monitor above their tank. A correct "shot" was rewarded with food. The fish were then shown the familiar face alongside up to 44 new faces. In these tests, the archerfish correctly identified the trained face with an accuracy of up to 81%. In a second experiment, where variables like color and head shape were standardized across the images, their accuracy increased to 86%.
Brains without a neocortex
This achievement challenges long-held ideas about the brain structures required for complex visual tasks. In humans and other primates, facial recognition is largely handled by the neocortex, a complex part of the brain that fish do not possess. The archerfish's ability to learn this skill suggests that specialized brain regions may not be a prerequisite for facial recognition. Instead, existing, more general-purpose neural circuits can be adapted for the task.
The archerfish has no evolutionary reason to recognize human faces, meaning this ability is a product of its impressive learning capacity, not an innate skill. This finding opens up new questions about the cognitive abilities of animals once considered to have "simple" brains. The study of the archerfish shows the fundamental mechanisms of vision and learning that may be shared by a wider range of vertebrates than previously understood.