テッポウウオは「人の顔」を見分けた。水鉄砲で虫を撃ち落とす魚の、意外すぎる頭のよさ

Archerfish live in rivers in Southeast Asia and Australia. They shoot water from their mouths to knock insects off leaves. In 2016, scientists showed pictures of human faces to these fish. The fish learned to spit water at one face, and not at another face, to get food.

Later, they could tell the face they knew apart from many new faces. Fish do not have the same brain parts as humans, but they can still tell faces apart.

Archerfish hunt by shooting jets of water at insects sitting above the surface. In 2016, Cait Newport and Ulrike Siebeck trained these fish to spit at one human face on a screen, and not at a second face, in order to get food.

Later, when the second face was shown together with 44 new faces, the fish could tell it apart from the new ones with high accuracy. This was surprising because fish do not have a neocortex, the brain area that plays a large role in human face recognition. Archerfish are also good at learning from each other. A 2006 study found that fish that had only watched another fish shooting could hit fast-moving targets too, even without practicing themselves.

Archerfish, found in mangrove waters of Southeast Asia and Australia, are famous for knocking insects off leaves with precisely aimed jets of water. Experiments show that their abilities extend well beyond marksmanship. In 2016, Cait Newport, Ulrike Siebeck, and colleagues trained archerfish to spit at one face displayed above their tank and to ignore another.

When the ignored face was later paired with 44 unfamiliar faces, the fish could tell it apart from the unfamiliar ones with high accuracy, and they still succeeded when 18 faces were adjusted so that color, brightness, and head shape gave no clues. Because fish lack a neocortex, the result suggests that recognizing faces may not require specialized brain structures.

Earlier, in 2006, Stefan Schuster's group showed that archerfish could learn to hit rapidly moving targets merely by watching a skilled companion. In 2014, the same group found that the fish adjust how their mouth opening changes so that water gathers at the tip of the jet just before it strikes, even at different distances. These studies, however, used only a few fish. The face task may reflect general pattern recognition rather than processing specific to faces.