The ability to recognize a reflection in a mirror as an image of oneself is considered a hallmark of cognition in animals. For this, there is a test, also known as a mirror self-recognition (MSR) test, which consists of marking an individual animal in a place on the body that is only visible when the individual sees it reflected in a mirror. If the animal investigates it or touches the mark, it is considered to have shown that it recognizes the mirror image as its own.
Are fish self-aware?
An international team of researchers led by Masanori Kohda of the Graduate School of Science, Osaka City University, Japan, has provided new evidence suggesting that fish have this ability and thus self-awareness. Very few species have passed the mark test. It is a trait that has so far only been conclusively demonstrated in chimpanzees and other great apes, some rays, dolphins or orcas.
“Previously, using a brown tag in the throat area of Labroides dimidiatus, we had shown that 3 out of 4 cleaner fish scraped their throats multiple times after swimming in front of a mirror ,” says Kohda, “a number on par with with similar studies done in other animals such as elephants, dolphins and magpies. However, one of the criticisms of this result was the size of the sample and the need for repeated studies showing positive results.
a larger sample
This study increased the sample size to 18 fish of this same species, with a positive result of 94% , that is, 17 of them showed the same behavior of the previous investigation, trying to scratch their throat when seeing the brown mark with the shape of parasite (but barely visible) on his body reflected in the mirror. Of course , the researchers also added a new step in the experiment to see if the fish would respond or not to a physical stimulus that was not visible, so they put green and blue visible marks in the same way as with the brown ones emulating parasites and they waited None of the fish attempted to scratch these marks , indicating that visual (rather than physical) perception of parasite-like markings was a likely explanation for the MSR fish scratching its throat.
“After looking at similar studies done on monkeys, pigs, dogs, cats, etc. that clearly tested negative, we wonder if the reason these animals did not pay attention to the tag was because it did not represent something in their natural environment that they would be concerned about. In our previous study, we used a brown mark as it may look like a small parasite that is a main food source for L. dimidiatus ,” the authors clarify.
Thus, by using a colored mark that resembled a parasite, the fish reacted to seeing the mark on their body reflected in the mirror. With the blue and green markings, none reacted.
“ We still have a lot of work to do, especially quantitatively, to show that fish, like other animals, have the capacity for MSR, however, as a result of this study, we reiterate the conclusion of our previous study that self-awareness in animals or the validity of the mirror test needs to be reviewed,” Professor Kohda concluded.
Referencia: Masanori Kohda, Shumpei Sogawa, Alex L. Jordan, Naoki Kubo, Satoshi Awata, Shun Satoh, Taiga Kobayashi, Akane Fujita, Redouan Bshary. Further evidence for the capacity of mirror self-recognition in cleaner fish and the significance of ecologically relevant marks. PLOS Biology, 2022; 20 (2): e3001529 DOI: 10.1371/journal.pbio.3001529
Masanori Kohda, Takashi Hotta, Tomohiro Takeyama, Satoshi Awata, Hirokazu Tanaka, Jun-ya Asai, Alex L. Jordan. If a fish can pass the mark test, what are the implications for consciousness and self-awareness testing in animals? PLOS Biology, 2019; 17 (2): e3000021 DOI: 10.1371/journal.pbio.3000021
