(ORDO NEWS) — Scientists have re-confirmed that wrasses pass the labeled mirror test, an experiment designed to test whether animals have self-awareness. This either indicates that the fish are indeed self-aware to some extent, or the interpretation of this test should be reconsidered, the authors of the study said.
The Marked Mirror Test is an experiment in which animals are given some sort of mark on a part of the body that they cannot see directly, then the animal is placed in front of a mirror and its behavior is observed.
If it starts touching the spot or tries to erase the mark, the researchers conclude that the animal has recognized itself in the mirror and is therefore somehow aware of itself.
So far, only experiments involving chimpanzees and some orangutans have shown convincing positive results, and passing the mirror test with elephants, dolphins, horses, crows and magpies has been observed only in isolated experiments and is still questioned.
However, in 2019, a group of researchers from Japan published an article for the first time that small fish, the wrasse of the species Labroides dimidiatus (also known as the common doctor wrasse) , successfully pass the mirror test.
Then the results of the experiments were subjected to versatile criticism, but the authors of the work did not give up, took into account the comments received, conducted a series of new experiments and published their results in a new article.
First of all, the scientists increased the experimental sample size to increase the statistical significance of the observed effects: in the new study, 17 out of 18 fish (94%) with brown marks on their throats tried to scrape them off by looking in the mirror, the same behavior was observed in previous experiments.
Further, the researchers responded to criticism that wrasses may not see the mark, but feel it and, accordingly, try to touch the place where they feel discomfort.
To test this, the researchers tried injecting the dye deeper into the skin—three millimeters instead of one, so that the mark was barely visible. This led to the fact that the behavior of the fish ceased to depend on the presence of a mirror – that is, they probably really stopped seeing the mark.
The authors of the work also showed that wrasses do not perceive the mirror as another fish: if instead of a mirror through one of the walls of the aquarium, the fish saw another individual with a mark applied, they did not try to clean the mark from their body.
Separately, the researchers tested that the color of the mark is important: wrasses reacted to brown spots, which are visually similar to the parasites they feed on, but not blue or green spots. Scientists suggest that this may be important for other species that have not yet passed the mirror test.
Thus, biologists were able to respond to criticism of previous experiments and more reliably show that wrasses are indeed able to pass the mirror test with a mark.
The authors of the article believe that these results, combined with the fact that some more highly organized species of animals – cats, dogs, pandas, some types of monkeys – do not pass the same test, indicate that self-awareness can manifest itself to varying degrees, and the mirror test cannot completely refute or prove its existence, and only highlights one of the aspects.
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