Rapid self-recognition ability in the cleaner fish | Scientific Reports

Whether animals are self-aware has important implications for our approaches to both animal cognition and animal welfare. A landmark moment in animal cognition research was when great apes passed the mark-test and demonstrated mirror self-recognition (MSR). Animals that pass the mark-test are capable of visually self-recognising and considered to be self-aware. Other taxa, including a fish, the cleaner wrasse (cleaner fish: Labroides dimidiatus) have also now passed the mark-test, forcing a rethink of the mental and neurological requirements for MSR. Previous research has largely focused on which species can pass the mark-test, rather than the processes underlying MSR. Here, we marked mirror-naïve cleaner fish with an ecologically relevant mark resembling an ectoparasite and then undertook detailed behavioural observations after exposure to a mirror. We found that cleaner fish achieve MSR rapidly, implying self-awareness prior to mirror exposure. By observing the exact timing of MSR in individuals, we could also report previously undocumented differences in pre- and post-MSR behaviours, including post-MSR exploratory behaviour of the mirror’s reflective properties. We find remarkable parallels between the processing of MSR in humans and cleaner fish, suggesting that some aspects of self-awareness are conserved across animal taxa.

Introduction Whether animals are self-aware has remained a popular yet controversial topic in both philosophy and the natural sciences. Although there are several definitions of the term self-awareness, we primarily use the term as per Kohda et al.1 but see Morin2. Two alternative hypotheses have been proposed to explain the possible evolution of self-awareness in vertebrate animals. One is a “Big Bang” hypothesis, which posits that true self-awareness evolved only once in the common ancestor of the great apes3. This first hypothesis was formulated based on observations by Gallup that…

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