"Fish Thought in Front of the Mirror" — The Challenge of "Self-Recognition" Presented by the Cleaner Fish

"Fish Thought in Front of the Mirror" — The Challenge of "Self-Recognition" Presented by the Cleaner Fish

In Front of the Mirror, the Fish "Froze"—And Thus the Story Began

"Recognizing oneself in the mirror." While this ability seems obvious to humans, in the world of animal cognition, it has long been treated as a "special boundary." The mirror test (mark test) proposed by Gordon Gallup is famous as a framework for exploring signs of self-recognition by observing whether animals like chimpanzees touch a "mark" on their bodies using the mirror as a clue.


However, there exists a creature that shakes this boundary. About the size of a finger, the Putzerfisch (Cleaner Wrasse/Labroides dimidiatus) is known as the "cleaner" of the sea. They eat parasites and dead skin off larger fish, playing an important role in the coral reef ecosystem. The behavior shown by this small fish in front of the mirror fundamentally questions "what is self-recognition."


What Does the Mirror Test Measure?—There Isn't Just One Sign of "It's Me"

The mirror test looks not just at whether there is a reaction to the mirror image but at whether the mirror is used as a source of information to check parts of oneself that are normally unseen and change behavior accordingly. A typical example is placing a colored mark in an unseen location and observing whether the animal addresses the mark only when a mirror is present.


However, this is where it gets tricky.

  • What About Animals That Can't Touch the Mark?

  • Isn't it too disadvantageous for animals that don't primarily rely on vision?

  • Doesn't it unfairly disadvantage animals that don't primarily rely on vision?


In other words, while the mirror test is convenient, it's hard to definitively say "no reaction to this test = no self-recognition." Conversely, it's also difficult to assert "reaction = presence of self-awareness." Criticism that the mirror test only looks at "one aspect of self-recognition" has existed for a long time.


The "Resemblance" Shown by the Putzerfisch—Attack → Examination → Self-Directed Action

A 2019 PLOS Biology paper reported on the Cleaner Wrasse's gradual change in behavior towards the mirror. Initially, they became aggressive, treating the mirror image as "another individual," then showed strange movements (contingency-testing-like behavior), and ultimately attempted to remove a colored mark placed in a position only visible in the mirror by rubbing their bodies.


This "attempting to address a mark in an unseen position only when a mirror is present" is quite close to the requirements of the classic mirror mark test. Moreover, since it is demonstrated through behavior (rubbing) that aligns with their ecology of "removing parasites," researchers argued that it is established as an ecologically meaningful task.


Research Continues: Recognizing "Self" by Face? Mentally Representing Body Size?

In recent years, research that further stimulates the debate has continued.


1) The Hypothesis of Mental Image of "One's Own Face" (PNAS, 2023)
The PNAS study suggested that Cleaner Wrasse might not be judging the mirror image solely by "movement matching" but possibly identifying themselves based on the features of their own "face." This claim, reminiscent of the framework of human self-face recognition, if valid, would elevate the dimension of "understanding the mirror."


2) Delving into "Mental Representation of Body Size" (Scientific Reports, 2024)
In the 2024 Scientific Reports, results were reported suggesting that individuals demonstrating mirror self-recognition (MSR) ability might mentally represent their body size and use it for situational judgment. Given that body size is involved in social ranking and strategic interactions among fish, the possibility of treating "how big am I" as an internal model is intriguing from a behavioral ecology perspective.


3) The Shock of "Passing in 30 Minutes" (Scientific Reports, 2025)
Furthermore, the 2025 Scientific Reports discussed the possibility that Cleaner Fish might reach mirror self-recognition very quickly, suggesting it is difficult to explain solely as a "product of learning." At this point, it's challenging to dismiss it merely as "mirror habituation."


Of course, these do not definitively state "there is self-awareness." However, at the very least, it appears that fish switch between "mirror = other" and "mirror = information source" to extract self-related information. The question is what to call it.


Is It Self-Awareness or Instrumental Reasoning?—The "Uncomfortably Sharp" Point by Frans de Waal

The intrigue of this debate lies in the fact that it's not a simple win or lose. Frans de Waal, known for his primate research, discusses the Cleaner Wrasse study, arguing that what the mirror test measures should be seen as gradual and continuous.


In essence, it boils down to this.

  • Do they conceptually understand the mirror as "themselves"?

  • Or are they merely "using the body information reflected in the mirror to solve the current problem (the parasite-like mark)"?


The latter is still advanced, but it might be different from the former. Indeed, even in the Max Planck commentary, there is a stance not to simplistically equate "passing the mirror test = self-awareness," questioning the "meaning" of the mirror test itself.


In other words, the Cleaner Wrasse challenges not only the question of "do fish have self-awareness?" but also **"is it appropriate to call the mirror test a 'self-awareness test'?"**


Reactions on Social Media: Surprise, Resistance, and Towards "Ethics"

 

This theme is popular on social media. The reason is simple: the phrase "fish self-recognition" is striking. Looking at actual posts, reactions broadly fall into three categories.


1) "Wow, Fish Are Too Smart" Category

In science news accounts and research introduction posts, expressions like "small fish recognize themselves in the mirror" and "distinguish themselves even in photos" tend to spread easily.


Here, the thrill of "overturning common sense" outweighs the fine reservations. Comment sections often get excited with remarks like "it's not just dolphins and elephants?" and "what's next?"


2) "Isn't That Just Reacting to a 'Parasite-Like Mark' Instead of Self-Recognition?" Category

In Reddit's science threads, excitement is always accompanied by skepticism. Comments like "where's the evidence they understand the mirror image as themselves?" and "isn't it conditioning?" appear, with a strong atmosphere of caution towards the validity of the mirror test and interpretative leaps.


Interestingly, the focus here tends to be more on "the rigor of test design and interpretation" rather than "believing in the fish." It feels like a collective intelligence reflexively applying brakes when the story gets too big, rather than high scientific literacy among netizens.


3) "So Is It Okay to Eat Fish? Is It Okay to Fish?" Category (Connecting to Ethics and Society)

The topic of self-recognition often spills over into animal welfare and fishing ethics. For instance, in the context of animal protection organizations, it easily ties into claims like "fish also feel pain and have cognition."


In this flow, the focus shifts from the research results themselves to "should our treatment change?" The moment scientific "discoveries" touch on lifestyle habits or industrial structures, the debate quickly heats up.


And Don't Forget the Fourth Force: "Meme-ification"

The topic easily lends itself to jokes like "fish looking in the mirror and self-reflecting" or "more self-aware than humans." On Reddit, there are many posts circulating with cute photos and provocative headlines, where "science" and "humor" coexist.


So the Conclusion: Do Putzerfisch Possess "Self-Awareness"?

To be honest, it's too early to definitively say "fish have human-like self-awareness" at this point. What passing the mirror test indicates is at least

  • They don't treat the mirror as just "another individual"

  • They can extract self-related information from the mirror image

  • They can convert that information into action
    which is a bundle of advanced cognition.


However, this is where the world becomes interesting.

If "self-awareness ≠ passing the mirror test," thenhow should we define "self-awareness"?.
If "self-recognition is continuous," thenwhere should the human-centered boundary be drawn?.


The Putzerfisch shows how far "intelligence required by the environment" can evolve, regardless of brain size or whether they are mammals. The small cleaner quietly peels away our assumptions in front of the mirror.


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