The cleaner wrasse is only the size of a human finger but it has become the first fish ever to pass the mirror test 鈥� a classic experiment used to gauge self-awareness in animals.
Until now, only relatively intelligent animals 鈥� including apes, dolphins, elephants and magpies 鈥� have passed the test, which demonstrates whether an individual can recognise itself. But in 2016, two manta rays were filmed checking out their reflections in a mirror in a fish tank, suggesting that聽 fish may be able to pass this test too.
To better test the self-awareness of fish, Masanori Kohda at Osaka City University, Japan, and his colleagues put 10 wild cleaner wrasses in individual tanks with a mirror. During the first few days, seven of the fish attacked their mirror images. But these fish then began to behave more unusually, dashing towards the mirror, and performing quick dances in front of it.
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These aren鈥檛 normal ways to behave in front of individuals from the same species, and had never been observed before.
As self-aware as elephants?
Eight of the fish were then tested further. The team injected a coloured gel onto part of each fish鈥檚 head, in a position where it could only be seen using the mirror. Following this, seven of the fish spent significantly more time in front of the mirror in postures that enabled them to observe the part of their head that had been marked. Some of them even tried to scrape the mark off.
According to the team, this means cleaner wrasses are as successful at recognising themselves in a mirror as elephants. 鈥淭his is the first report of successful passing of the mark test in vertebrates outside of mammals and birds,鈥� they write.
The team say their findings support theories that the ability to recognise oneself is more related to an animal鈥檚 social and behavioural factors than its brain size or how closely related to humans it is. However, they acknowledge that the mirror test has limitations 鈥� the fish seem able to use their reflection to look at themselves, but this tells us nothing about whether they are also aware of their own internal thought processes.
However, Gordon Gallup of the University at Albany, New York, who invented the mirror test, is not convinced. In the wild, cleaner wrasses eat parasites living on the skin of other fish. The wrasses in this experiment probably mistook the marks on their skin for parasites on the skin of other fish, Gallup says.
搁别蹿别谤别苍肠别:听
