Cleaner wrasse (*Labroides dimidiatus*) sometimes attack their reflection before displaying behaviors researchers interpret as mirror self-recognition. The sequence can look like a fish “flexing” before a fight, but the experiments do not show a deliberate pre-fight pose—and passing a mirror test does not by itself prove that a fish has human-like self-awareness or consciousness.
Why does a fish fight its reflection?
A mirror presents a fish with an image that moves as it does, but at first the reflection may be treated as another fish. Cleaner wrasse have been observed attacking or biting the mirror image, followed by repeated, unusual interactions and self-directed behaviors such as close viewing. The aggression is consistent with an initial social response; on its own, it is not evidence that the fish recognizes itself. The 2019 study and a Max Planck Society account describe the broader sequence.
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“Flexing” is a catchy shorthand, not a formal description of a measured behavior. The evidence does not establish that a fish plans to fight, poses for its reflection, or feels vanity.
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The mirror mark test asks whether an animal can use its reflection to respond to a mark on a part of its body it cannot normally see. In the 2019 experiment, researchers placed a colored mark where a fish could see it in the mirror. After viewing its reflection, the fish scraped its body against a surface—a behavior the study authors interpreted as an attempt to remove the mark.
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The reported controls help explain why the authors drew that conclusion: the scraping response was not observed with a transparent mark when a mirror was present, or with a colored mark when no mirror was present. The result supports the interpretation that the fish used visual information from the reflection to guide mark-directed behavior. It does not directly reveal what the fish consciously experienced.
Does passing the mirror test prove a fish is self-aware?
No single mirror-test result settles that broader question. The test measures behavior under particular experimental conditions; researchers must infer the mental capacity behind it. A fish that uses a reflection to act on its own body may show mirror self-recognition in the test’s operational sense, but that does not establish subjective consciousness, a human-like sense of identity, or what being a fish feels like.
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Interpretation of the cleaner wrasse result is disputed. In a 2019 commentary, Frans de Waal argued that the mark might be physically irritating and that scraping is not equivalent to the mark-directed visual inspection seen in some other species. These are questions about both the procedure and what behavior should count as evidence of self-recognition.
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What have later cleaner wrasse studies added?
Follow-up studies have examined other behaviors that may reveal how cleaner fish process information about themselves. They extend the evidence beyond the original mark test, but each concerns a specific reported capacity rather than resolving the broader question of fish consciousness.
- A 2022 study reported further evidence and addressed concerns about mirror exposure and mark color.
- A 2023 study reported that cleaner fish recognized their own photographs after mirror-test experience, with responses varying according to the face shown.
- A 2024 study reported that cleaner fish used a mental image to estimate body size.
- A 2025 study reported rapid self-recognition.
These findings concern photograph recognition, body-size assessment, and speed of performance. They are relevant evidence about the fish’s behavior and information processing, not a final answer about conscious experience.
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