If a fish can pass the mark test, what are the implications for consciousness and self-awareness testing in animals?

Abstract

The ability to perceive and recognise a reflected mirror image as self (mirror self-recognition, MSR) is considered a hallmark of cognition across species. Although MSR has been reported in mammals and birds, it is not known to occur in any other major taxon. Potentially limiting our ability to test for MSR in other taxa is that the established assay, the mark test, requires that animals display contingency testing and self-directed behaviour. These behaviours may be difficult for humans to interpret in taxonomically divergent animals, especially those that lack the dexterity (or limbs) required to touch a mark. Here, we show that a fish, the cleaner wrasse Labroides dimidiatus, shows behaviour that may reasonably be interpreted as passing through all phases of the mark test: (i) social reactions towards the reflection, (ii) repeated idiosyncratic behaviours towards the mirror, and (iii) frequent observation of their reflection. When subsequently provided with a coloured tag in a modified mark test, fish attempt to remove the mark by scraping their body in the presence of a mirror but show no response towards transparent marks or to coloured marks in the absence of a mirror. This remarkable finding presents a challenge to our interpretation of the mark test—do we accept that these behavioural responses, which are taken as evidence of self-recognition in other species during the mark test, lead to the conclusion that fish are self-aware? Or do we rather decide that these behavioural patterns have a basis in a cognitive process other than self-recognition and that fish do not pass the mark test? If the former, what does this mean for our understanding of animal intelligence? If the latter, what does this mean for our application and interpretation of the mark test as a metric for animal cognitive abilities?Editor’s noteThis Short Report received both positive and negative reviews by experts. The Academic Editor has written an accompanying Primer that we are publishing alongside this article (https://doi.org/10.1371/journal.pbio.3000112). The linked Primer presents a complementary expert perspective; it discusses how the current study should be interpreted in the context of evidence for and against self-awareness in a wide range of animals.

Directly Valuing Animal Welfare in (Environmental) Economics

“…Dogs, for instance, pay relatively little attention to other dogs' visual aspects, as they mostly care about how they smell (Rogers and Kaplan 2004). A recent study indicates that a species of fish may pass the test (Kohda et al 2019), and concludes that this finding challenges our common interpretation of the mirror test: "Do we accept that these behavioural responses, which are taken as evidence of self-recognition in other species during the mark test, lead to the conclusion that fish are self-aware? Or do we rather decide that these behavioural patterns have a basis in a cognitive process other than self-recognition and that fish do not pass the mark test?…”

Mental representation and episodic-like memory of own actions in dogs

“…rats 8 ; dolphins 9 challenge the view that any form of self-representation evolved only in primates. The traditional methodological approach to study self-representation is the mirror self-recognition paradigm that has been applied not only to apes 7 , but also to other species (including elephants 10 ; dolphins 11 ; magpies 12 cleaner wrasses 13 ). However, this paradigm may reveal only a single aspect of self-representation: visual recognition of one's own image (cf.…”

The illusion of science in comparative cognition

“…This contrasts with the vast swathes of methodological criticism in the field (e.g. Byrne, 2002;Guez & Audley, 2013;Hennefield, Hwang, Weston, & Povinelli, 2018;Heyes, 2015;Heyes, 1993;Kohda et al, 2019;Penn & Povinelli, 2007;Redshaw et al, 2017;Silva, Page, & Silva, 2005;Silva, Ten Hope, & Tucker, 2014;van der Vaart, Verbrugge, & Hemelrijk, 2012), which are examples of the postexperimental consideration of less exceptional explanations we described above. On the whole, if a comparative cognition study confirms a more exceptional theory, it is taken to say something general about that animal's abilities.…”