New experiments confirm that fish have self-awareness

Three years ago, a team of Japanese scientists published in the journal PLoS Biology some surprising and unusual results: some small fish Recife (Labroides dimidiatus)specialized in cleaning up parasites and dead skin from other people, had passed the self recognition in the mirror.

Our results reject criticisms about the ability of fish for self-recognition in the mirror, and indicate that they should be included in the group of animals with this ability.

Masanori Kohda, Osaka City University

This test, considered evidence of self-awareness, consisted of making a brown mark in a place on the body – usually the throat region – that they could only see indirectly in their reflection. Of the four animals with which the experiment was carried out – a figure similar to that of other studies carried out with other animals – three touched or scratched the signal after swimming towards the mirror, thus confirming the fish’s ability to self-recognition.

The work was a milestone, as few animals, most of them with large brains – among which the chimpanzeesThe dolphinsThe asian elephants and the handle–, they had demonstrated this ability until then.

Despite this finding, the investigation was criticized s questioned for several reasons; the main one is that it had been carried out in small fish, the most primitive vertebrates with small brains. The other comments questioned the sample size (n=4), that subjects might consider the mirror images as known individuals rather than themselves, and that the tag could provide a physical stimulus to the fish.

“Therefore, there may have been errors in the methodology”, he confesses to SINC Masanori Kodafrom Osaka City University’s Graduate School of Science in Japan. Now, the expert presents new evidence in a new study, published in the same journal, where he rejects all criticism and firmly supports the conclusions of his first work.

“Our results reject the critics about the ability of self-recognition in the mirror of fish, and indicate that fish should be included in the group of animals with this ability”, says Kohda.

Furthermore, the new research suggests that “many other vertebrates could pass the mark test and have self-awareness, something not previously appreciated,” he continues.

According to Japanese scientists, in collaboration with researchers from the Max Planck Institute for Animal Behavior, in Germany, and University of Neuchatelin Switzerland, the work is “an advance for the studies not only of animal cognitionbut also psychology, which considers that only human beings have self-awareness”, they emphasize.

Bigger sample, more evidence

To corroborate their results, the experts increased the sample size to 18 cleaner fishwith a positive result of 94%, that is, 17 of them showed the same behavior as in the previous study.

In the first work, the scientists performed a brown mark in fish because it can look like a small parasite, which is their main food source. They made this decision after looking at similar studies done on monkeys, pigs, dogs or cats, with negative results, where they realized that perhaps the signal in these animals “didn’t represent something in their natural environment that they were concerned about,” says Koda. .

Fish are self-aware, like chimpanzees, or even humans, suggesting that fish have a ‘mind’

Masanori Kohda, Osaka City University

To respond to criticism about the tag, whose physical sensation could trigger the behavior, the team tested the fish’s response to a physical stimulus in its throat by injecting the brown tag 3 mm deep (instead of 1 mm). There the mark was barely visible, however, they discovered that the fish with the injection The deeper ones scratched their throats at a similar pace whether there was a mirror or not.

In order to further cement the importance of using eco-relevant tags for animals in these types of studies, the team found that no fish injected with green or blue tags demonstrated scraping behavior.

But how can fish know that they are the ones who appear in the mirror and not the others? An animal looking at its reflection goes through three states: first it expresses an aggressive behavior –as it likely perceives the image in the mirror as another animal does–, then it shows an unnatural but nonaggressive movement–since it confirms that the image in the mirror is correct. correct, the mirror is not another animal – and finally it repeatedly looks at its own body without aggression.

At this last point is when the self recognition it is possible, because the fish can see the mark and try to scrape it off. This happened in the first work with L. dimidiatusbut the question was whether moving the mirror might reignite his aggression.

To test this, the team transferred the cleaner fish to a tank with a mirror on one side and, three days later, to a tank with a mirror on the other side. In none of the containers the fish showed aggression to their own image.

“Fish are self-aware, like chimpanzees, or even like humans, which suggests that fish have a ‘mind,’” Kohda tells SINC. However, there is still a lot of work to be done, especially qualitatively, to continue demonstrating that fish, like other animals, have the capacity for self-recognition.