Fish Use Mirrors to Assess Size Before Deciding to Fight

Bluestreak cleaner wrasse demonstrate self-awareness by checking their reflection to gauge body size against potential rivals.

Researchers observed bluestreak cleaner wrasse using mirrors to assess their body size before deciding whether to engage in a fight.
The study, published in Scientific Reports, suggests these fish possess elements of private self-awareness, such as mental body image and intentions.
Cleaner wrasse were found to attack only smaller fish after checking their reflection, indicating they use the mirror as a decision-making tool.
This behavior marks the first non-human instance of animals using mirrors to inform decisions, providing insights into the evolution of self-awareness.
The findings build on previous research showing that cleaner wrasse can recognize themselves in photos and pass the mirror self-recognition test.