Rosa Rubicondior: Refuting Creationism - Cleaner Wrasse Have Mammal-Like Cognitive Abilities

Cleaner wrasse with giant moray eel client

By Silke Baron - originally posted to Flickr as Giant Moray Eel getting cleaned,
CC BY 2.0, Link

Cleaner fish show intelligence typical of mammals | Osaka Metropolitan University

A central dogma of creationism—indeed one reason why it persists and is clung to in the face of contrary evidence, massaging the egos of creationists—is the claim that humans were uniquely created, separate from and superior to other animals. Until the middle of the 20th century, humans were believed to possess unique abilities to make and use tools, to learn and design, and above all to be self-aware—qualities that religious people believed placed us next to God in possessing these abilities because we had been created in its image.

Since then, one formerly unique human ability after another has been shown to be possessed by other animals, mainly, but not exclusively, mammals and birds. Many species are now known to use tools and some are even known to make them. And many have been shown to be self-aware, using the 'mirror test' in which an animal can identify the image in the mirror as itself—see the information in the side panel for many examples of other animals with these formerly 'unique' human abilities.

Now a team of researchers, led by Dr. Shumpei Sogawa and Professor Masanori Kohda of Osaka Metropolitan University, Osaka, Japan, have shown that a fish, the cleaner wrasse, shows evidence of self-awareness according to the mirror test. These small fish specialise in removing parasites from the bodies of larger fish, even entering the mouths of predators to remove food particles and parasites from between the teeth and on the gills of their 'clients'. The Osaka-led team recently published their findings, open access, in the journal Scientific Reports.

Background^ The Mirror Test and Animal Self-Awareness.
The mirror self-recognition (MSR) test, often called the mirror test, was first developed in 1970 by psychologist Gordon Gallup Jr. as a way of investigating whether animals possess a degree of self-awareness.

In the test, an animal is secretly marked with a coloured spot or sticker in a place it cannot normally see, such as on the forehead or throat. The animal is then given access to a mirror. If it uses the mirror to investigate or attempt to remove the mark on its own body, rather than treating the reflection as another animal, researchers interpret this as evidence that the animal recognises the reflection as itself.

Humans typically begin passing the mirror test at around 18–24 months of age, making it one of the earliest experimental indicators of self-awareness in children.

For many years it was assumed that humans were the only species capable of this level of self-recognition, reinforcing the belief that humans were fundamentally different from other animals. However, research over the last few decades has shown that several other species can also pass the test.

Animals that have demonstrated mirror self-recognition include:

Great apes (chimpanzees, bonobos, orangutans)
Dolphins
Asian elephants
Magpies (Pica pica, a member of the crow family)
Cleaner wrasse (Labroides dimidiatus)

The cleaner wrasse result was particularly surprising because fish brains are organised very differently from those of mammals and birds. This suggests that the cognitive abilities required for mirror self-recognition may have evolved independently in different animal lineages, rather than appearing only once in human evolution.

Some researchers also argue that the mirror test may be biased toward animals that rely heavily on vision, meaning that other intelligent animals may fail the test despite possessing forms of self-awareness expressed through other senses.

Other “Uniquely Human” Traits Found in Animals

Over the last century, a growing list of abilities once thought to distinguish humans from all other animals has turned out to be far more widespread in the animal kingdom.

Tool use and manufacture

Once thought to be uniquely human, tool use is now known in many species.

Examples include:

Chimpanzees using sticks to fish termites from nests
New Caledonian crows shaping hooks from twigs to retrieve insects
Sea otters using stones to crack open shellfish
Octopuses collecting coconut shells for shelter

Some species not only use tools but modify or manufacture them, indicating foresight and planning.

Problem solving and planning

Many animals show sophisticated reasoning abilities.

Examples include:

Ravens solving multi-step puzzles
Scrub jays storing food and remembering future needs
Chimpanzees planning sequences of actions to obtain food
Bumble bees pulling on string to retrieve a reward - also shown to teach other bees.

Experiments have even shown some animals saving tools for future use, suggesting a form of planning previously thought to be uniquely human.

Communication and symbolic understanding

Human language is unique in its complexity, but elements once thought exclusive to language appear elsewhere.

Examples include:

Dolphins using individual signature whistles functioning much like names
Prairie dogs producing alarm calls that encode detailed information about predators
Great apes learning hundreds of symbols or signs in laboratory settings
Honey bees use the 'waggle dance' to convey information about the direction and distance to nectar-producing flowers

These findings suggest that the evolutionary roots of language lie in more ancient communication systems shared with other animals.

Empathy and social awareness

Evidence for emotional awareness and empathy has also been found in many species.

Examples include:

Elephants comforting distressed companions
Rats freeing trapped cage-mates
Primates consoling individuals after conflicts

These behaviours indicate that complex social emotions are not unique to humans.

Evolution, Not Exceptionalism

These discoveries show that many cognitive abilities once used to justify the belief that humans are fundamentally separate from the rest of the animal kingdom are actually variations of capacities that evolved gradually across different lineages.

Rather than appearing suddenly in humans, traits such as tool use, planning, empathy and even self-recognition appear to be products of evolution acting on social and ecological challenges, producing similar solutions in very different species.

So something that was once thought unique to humans has now been shown to be shared by a fish to which we are only very distantly related, sharing a common bony-fish ancestor in the Late Silurian.

And so another characteristic that supposedly 'proved' we were created in the likeness of a god, materially different from all the other species, proves once again to be nothing of the sort.

The work of the Osaka team is also explained in an Osaka Metropolitan University Research News item.

Cleaner fish show intelligence typical of mammals
Cleaner wrasse show two hallmarks of self-awareness: speedy self-recognition and contingency testing intelligence

A cleaner wrasse in front of a mirror.

Credit: Osaka Metropolitan University.

Fish interacting with a piece of food in the mirror
The cleaner wrasse picks up a piece of shrimp and drops it in front of the mirror. As the food falls, the fish repeatedly touches the glass of their tank with their mouths seeming to explore the mirror itself.

Credit: Shumpei Sogawa, Osaka Metropolitan University

Researchers at Osaka Metropolitan University in Japan have discovered a previously undiscovered behavior in cleaner wrasse (Labroides dimidiatus). When presented with a mirror, the tiny fish not only recognized themselves, but experimented with the mirror themselves, interacting with it using a scrap of food. The results suggest that these social fish can perform a higher level of intelligence known as ‘contingency testing,’ typically seen in intelligent marine mammals like dolphins.

The group led by Specially Appointed Researcher Shumpei Sogawa and Specially Appointed Professor Masanori Kohda at the Graduate School of Science—who previously showed that wrasse can recognize themselves in photographs—observed the behavior during mirror test experiments. These tests are a common way to test cognition in animals and previous studies have shown that cleaner wrasse recognize themselves in the mirror.

First, the research group applied markings that resembled parasites to cleaner wrasse. They found that even wrasse that had never seen their reflection in a mirror before quickly learned to use the mirror to clean off the ‘parasite.’

Even here there were surprising findings as the cleaner fish responded remarkably quickly — in some cases within the first hour of seeing the mirror. The group found that the behavior of attempting to rub off the mark was observed within an average of 82 minutes, much faster than the 4 to 6 days in previous experiments.

In earlier cleaner wrasse mirror studies, the procedure was typically the fish see a mirror for several days, they habituate to it and stop reacting socially, and a mark is added. In this study, the order was reversed, the fish were marked first, then the mirror was introduced for the first time. The fish were likely aware of something unusual on their body, but they couldn’t see it. When the mirror appeared, it immediately provided visual information that matched an existing bodily expectation, hence scraping occurred much faster.

Dr. Sogawa explained, lead author.
Laboratory of Animal Sociology
Department of Biology
Graduate School of Sciences
Osaka Metropolitan University
Osaka, Japan.

More unexpected, however, was the next behavior. After several days of mirror exposure, some of the fish were seen picking up a small piece of shrimp from the tank floor, carrying it upward, and deliberately dropping it near the mirror. As the shrimp sank, the fish closely followed its descent along the mirror surface, repeatedly touching the glass with their mouths while watching the shrimp’s descent in the reflection.

The researchers interpreted this as a form of ‘contingency testing,’ an advanced behavior where instead of testing the mirror with their own bodies, an animal tests how external objects behave in mirror space. By dropping shrimp and watching how its movement corresponded with its reflection, the fish were exploring the mirror itself. Similar behaviors have been reported in other marine animals such as manta rays and dolphins that release bubbles and watch them rise in mirrors.

Importantly, this kind of exploratory testing strengthens the case that the mirror-directed actions seen in cleaner wrasse are grounded in flexible, self-referential processing rather than simple confusion or learned associations.

These findings in cleaner wrasse suggest that self-awareness may not have evolved only in the limited number of species that passed the mirror test but may be more widely prevalent across a broader range of taxonomic groups, including fish. It is highly likely that mirror self-recognition will be observed in many species where mirror tool use has been reported.

Dr. Sogawa explained.

Going forward, the researchers believe that research on self-awareness across all animals, including invertebrates, will become increasingly important.

The findings from this research will likely influence not only academic issues, such as revising evolutionary theory and constructing concepts of self, but also directly impact matters relevant to our lives, including animal welfare, medical research, and even AI studies.

Professor Masanori Kohda, co-corresponding author.
Laboratory of Animal Sociology
Department of Biology
Graduate School of Sciences
Osaka Metropolitan University
Osaka, Japan.

Publication:
Sogawa, S., Kobayashi, T., Bshary, R. et al.
Rapid self-recognition ability in the cleaner fish. Sci Rep 15, 41882 (2025). https://doi.org/10.1038/s41598-025-25837-0

Abstract
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.

Sogawa, S., Kobayashi, T., Bshary, R. et al.
Rapid self-recognition ability in the cleaner fish. Sci Rep 15, 41882 (2025). https://doi.org/10.1038/s41598-025-25837-0

Copyright: © 2025 The authors.
Published by Springer Nature Ltd. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)

Yet again, a supposedly uniquely human trait invoked to justify the belief that humans were specially created turns out to be nothing of the sort. Instead of a sharp boundary separating humanity from the rest of the animal kingdom, what we see is a continuum of cognitive abilities evolving in different lineages under different ecological pressures.

The discovery that even a small fish can show behaviour consistent with self-recognition should come as no surprise to evolutionary biologists. Evolution does not work by granting one species a sudden monopoly on complex abilities. Rather, natural selection favours whatever behavioural or cognitive traits help organisms survive and reproduce in their particular environments. Over millions of years, similar problems often produce similar solutions, even in very distantly related animals.

What this research illustrates once again is that humans are not an isolated creation, fundamentally separate from other life forms. We are one branch on a vast evolutionary tree, sharing ancestry with all other living things and sharing many traits with them as well. The differences between species are differences of degree, not of kind.

And with every new discovery like this, another small piece of the creationist myth of human exceptionalism quietly slips away, replaced by a far more interesting and evidence-based picture of life evolving on Earth.

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