Fish sizes itself up in a mirror before going into combat

Fish, of all the creatures, have discovered the power of introspection. "Mirror, mirror on the wall, who's the fairest fish of all?" seems to be the question on every bluestreak cleaner wrasse's mind, according to an intriguing new study.

Imagine stumbling upon a fish meticulously gauging its size in the mirror before deciding if it should attack another fish.

That is precisely the kind of behavior that was observed in the bluestreak cleaner wrasse, a brilliantly colored finger-sized coral reef fish.

This finding, which is the first of its kind, dethrones the belief that such levels of self-awareness are exclusive to higher mammals.

Mirror test of fishes

Scientists have used the "mirror test" as a classic indicator of an animal's self-awareness, measuring whether the creature recognizes its reflection as its own. This new study shows that the cleaner wrasse doesn't just recognize itself, it's also sizing itself up.

The research group, including Osaka Metropolitan University Graduate School of Science student Taiga Kobayashi, set up a series of tests.

The tests were designed to assess the fish’s propensity to attack when faced with an image of another fish, either 10% larger or smaller than themselves.

"Regardless of the size of the fish in the photo, the real ones attacked," reported the researchers.

But, here's where it gets interesting. The presence of a mirror influenced the decision of whether to attack or not. After checking their reflection, the fish opted to lock fins with the smaller fish's image and steered clear of the larger one.

Surprising level of self-awareness

This study raises several intriguing questions. Chief among them - how did the bluestreak cleaner wrasse, living in a world devoid of mirrors, evolve to use its reflection as a decision-making tool?

One possible theory points to the benefits of sizing themselves against a potential threat before attacking.

"These findings suggest that cleaner fish likely possess two mental states: a mental image of their body and internal standards for comparing body size," said Kobayashi.

Could the survival instincts have led to the development of this surprising level of self-awareness?

Self-recognition in fish

The discovery of the bluestreak cleaner wrasse's ability to engage in self-reflection prompts a reevaluation of evolutionary theories regarding self-recognition.

Traditionally, self-awareness has been considered an advanced cognitive trait emerging in species with complex social structures and large brains. However, the relatively small-brained cleaner wrasse challenges these assumptions.

This revelation invites scientists to explore alternative evolutionary pathways that may have led to the development of self-awareness in fish.

Could it be that ecological demands, such as complex social interactions within the reef environment, have driven the evolution of this cognitive skill?

These questions highlight the broader implications of this study, offering a new lens through which to investigate the cognitive lives of aquatic species.

Broader conservation efforts

Extending the insights gained from this study beyond the realm of fish , the compelling evidence of advanced cognitive abilities in the bluestreak cleaner wrasse encourages a broader examination of animal cognition.

By highlighting the sophistication of fish intelligence, this research may pave the way for a more inclusive understanding of biodiversity, emphasizing the cognitive capacities across various species.

These findings on fish using mirrors could influence conservation efforts by advocating for the preservation of species that display complex behavioral traits.

Recognizing the mental worlds of creatures like the cleaner wrasse might inspire a wave of appreciation and protection for marine life, prompting further studies to uncover the depths of animal cognition nestled within the world's oceans.

A new understanding of self-awareness

The cleaner wrasse's behavior broadens our understanding of self-awareness, not just in animals, but also in humans.

Can we draw parallels between human and animal self-awareness? Could this fishy behavior shed light on how self-awareness evolved over time?

"The results that fish can use the mirror as a tool can help clarify the similarities between human and non-human animal self-awareness and provide important clues to elucidate how self-awareness has evolved," said Kobayashi.

The study is published in the journal Scientific Reports .

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