New experiments confirm that fish are self-aware

(ORDO NEWS) — Of the 18 fish, 17 responded to a visual cue in the form of a mark on their body when they were presented with a mirror during the study.

Mirrored self-awareness (MRS) is seen as evidence of self-awareness, and passing the mark test, in which animals touch or scratch a tag located on their body at a location that can only be indirectly seen in a mirror, is used to determine the ability of an animal to MR.

Apart from the chimpanzee, the evidence that other animals passed the mark test has been criticized and therefore inconclusive.

Responding to criticisms of their previous work on the pure fish Labroides dimidiatus, an international team of researchers led by Masanori Kohda from the Osaka University Graduate School of Life Sciences has provided further evidence that fish have the ability to MCP.

The results of this new experiment were recently published in the journal PLOS Biology.

Prof Kohda says: “We have previously shown that three out of four clean fish scratch their throat several times after swimming in front of a mirror using the brown throat marking of L. dimidiatus, which is in line with similar studies done on other animals such as elephants, dolphins and magpies.”

However, one of the criticisms raised against this result was the sample size and the need for repeated studies showing positive results.

Teaming up with researchers from the Max Planck Institute for Animal Behavior in Germany and the University of Neuchâtel in Switzerland, the study authors increased the sample size to 18 pure fish, with a 94% positive result: 17 of them showed the same behavior as in the previous study.

But why the brown mark? “After looking at similar studies done on monkeys, pigs, dogs, cats, etc., which gave a clear negative result, we wondered if the reason that these animals do not pay attention to the mark is that it does not represent something in their natural environment that could disturb them,” says Professor Kohda.

“In our previous study, we used the brown mark as it may look like a small parasite that is the main food source for L. dimidiatus.”

A criticism in response to this has been the possibility that the physical sensation of the mark, as well as seeing the brown mark in the mirror, may induce behavior that is not conclusive evidence of MCP.

To address this issue, the team tested how the fish would respond to a physical stimulus in the throat by inserting a brown mark at a depth of 3mm (as opposed to 1mm). At this depth, the mark was barely visible, however, fish with a deeper injection were found to scrape their throats with the same frequency, regardless of whether a mirror was present or absent.

To further reinforce the importance of using environmentally appropriate animal tags in MCO studies, the team found that none of the fish that were given either green or blue tags exhibited scraping behavior.

Finally, some critics have questioned whether L. dimidiatus recognizes the mirror image as itself and not another fish. A mirror-learning animal is an animal that is introduced to a mirror image of itself and goes through three stages.

At first, the animal exhibits aggressive behavior as it probably perceives the mirror image as another animal; then it shows unnatural but non-aggressive movements, as it confirms that the mirror image is not another animal; and finally, it repeatedly examines its own body without aggression. At this point, MNR becomes possible, as the animal can see the mark and try to scrape it off.

Professor Kohda said,

“Our previous study demonstrated MSR in L. dimidiatus; however, studies with other animals showed that simply moving the mirror resumed aggressive behavior, suggesting that the animal only learned spatial matching and not MSR.”

To solve this problem, the team transplanted mirror-trained clean fish into an aquarium with a mirror on one side, and three days later into an aquarium with a mirror on the other side, and saw that the fish were not aggressive towards their mirror image in both tanks.

In addition, to ensure that L. dimidiatus that passed the mark test actually recognized themselves, the mirror-trained fish were placed in adjacent aquariums separated by clear glass.

Two or three days later, when the fish had largely reduced their aggressive behavior towards each other, they were tagged the next night in the standard way. None of the fish scratched their throats during the 120 minutes of exposure to each other the next morning.

“This result suggests that a visual, environmentally significant stimulus from another fish is not enough to cause throat grinding in tagged individuals,” says Prof Kohda.

“We still have a lot of work to do, especially quantitative work, to show that fish, like other animals, have the ability for MSR; however, as a result of this study, we confirm the conclusion of our previous study that either self-awareness in animals or the validity of the mirror test needs to be revised.”

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