It is considered a special ability of some highly developed animal species. But are there also fish that pass the famous mirror test? As one study shows, the cleaner fish shows signs of self-awareness in the mirror. The animals try to remove stains from their bodies when they become visible in the mirror. To what extent they have ego-consciousness remains unclear. Because the informative value of the mirror test for the detection of self-awareness in animals is questionable, say the researchers.
“What do I have on my face?” People understand the function of a mirror from around the age of two. Great apes and a few other highly developed animal species also have this ability to see themselves in the mirror. The so-called point test is proof of this: if you paint a point in the face of a chimpanzee who is familiar with mirrors, for example, he will be amazed at the sight and touch the point on himself. Elephants also do this with their trunks and magpies use claws: the intelligent birds scratch themselves at the marked area.
Amazing behavior in front of the mirror
The researchers led by Alex Jordan from the Max Planck Institute for Ornithology in Radolfzell have reported comparable behavior in cleaner fish (Labroides dimidiatus). The name of these animals says it all: They feed on parasites on the skin of other fish. As part of their study, the biologists first familiarized their test animals with their own reflection. For the point test, they then marked the fish on a part of the body that they could only see in the mirror. Since fish have no limbs to touch the point, the researchers assessed a special behavior as an indicator for passing the point test: When the fish rubbed the marked area on surfaces to remove the paint.
As the researchers report, the cleaner fish actually tried to get rid of the spots on their skin in this way. The control experiments also made the special behavior in connection with the mirror image clear: if the researchers provided the fish with spots but did not give them a mirror, they did not show the abrasion behavior. In addition, they did not react to other marked conspecifics or to spots directly on the mirror. “Through various observations we can rule out that the fish react instinctively to markings in their environment that are reminiscent of parasites. Only the sight of spots on its own skin is therefore a stimulus for a cleaner fish to which it reacts. This means that the cleaner fish’s behavior meets all the criteria for a passed mirror test, ”summarizes Jordan.
Result raises questions
But do the results prove that cleaner fish also have an awareness of their own self? “It remains unclear so far whether one can conclude on the basis of the results that some fish are self-conscious – even if in the past many animals were ascribed self-awareness after they had passed the mirror test,” says Jordan. According to the behavioral scientist, it is possible that other skills can lead to passing a mirror test as well. “The obvious explanation is that although the fish pass the mirror test, they are not self-aware. Rather, they recognize their reflection as an image of their own body, but do not understand what it means. So we have to critically question the mirror test and consider whether it can be used as the standard for the self-awareness test in animals, ”commented Jordan on the results of the study.
Source: Max Planck Institute for Ornithology, specialist article: PLOS Biology, doi: 10.1371 / journal.pbio.3000021