Fish can identify own image in a mirror, Osaka researchers find

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Fish can recognize themselves in a mirror, proving they are self-aware, Osaka City University researchers found.

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The cognitive abilities of chimpanzees, dolphins and other species have been widely reported, but this is the first evidence of the trait in fish.

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The findings of the team, headed by Masanori Koda, a professor of behavioral ecology and animal ecology, were posted in Plos Biology, a U.S. biological science journal, on Feb. 8.

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The researchers conducted a self-recognition test on bluestreak cleaner wrasses, a small tropical reef fish that inhabit coastal areas in southern Japan, using specimens raised in an aquarium.

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At first, immediately after a wrasse was shown a mirror, it moved to attack the “invader,” providing proof that it took its own reflection to be another fish.

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Later, however, it apparently tested that impression, doing things such as turning upside down. On the experiment’s fifth day and after, it reacted in this way less and less.

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Koda’s team then applied a brown mark on the bodies of four fish that had gone through the first experiment.

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After looking at the mirror, three wrasses scraped their bodies along the bottom of the fish tank.

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The researchers concluded from this reaction that the fish knew the image in the mirror was their own, because they tried to dislodge the mark, which resembled a parasitic insect.

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