Mirror-Match: Fish Assess Size for Fight Victory

Before engaging in a confrontation with another fish, cleaner wrasse engage in a peculiar ritual of self-assessment by studying their own reflection in a mirror.

Bluestreak cleaner wrasse, scientifically known as Labroides dimidiatus, display a remarkable level of intelligence. These diminutive coral reef inhabitants were the first fish species to pass the mirror test, signifying their ability to recognize their own reflection. Recent studies reveal that these wrasse utilize their mirror image to create a mental representation of their body size, enabling them to compare and contrast with others.

Researchers, led by Taiga Kobayashi from Osaka Metropolitan University, conducted experiments to evaluate the fish’s aggression levels. When presented with images of other wrasse differing in size, the territorial wrasses consistently initiated aggression, yet their response altered when a mirror was introduced. The fish exclusively engaged in battle with smaller mirror reflections, defying previous assumptions.

By refining their decision-making process through the mirror, cleaner wrasse display cognitive abilities beyond their evolutionary expectations. Understanding self-identity and size comparison in the absence of mirrors showcases their adaptive intelligence, proving their capability to utilize external reflections for strategic advantage.