Bluestreak cleaner wrasse are small, territorial fish that aggressively fend off intruders. But when they have access to a mirror, the fish size themselves up before deciding whether or not to fight.

Before deciding whether or not to fight another fish, cleaner wrasse check their own reflection in a mirror and size themselves up. First, Taiga Kobayashi at Osaka Metropolitan University in Japan and ...

New findings suggest bluestreak cleaner wrasse understand how their body size stacks up against a rival Sarah Kuta Daily Correspondent Bluestreak cleaner wrasse are small, territorial fish that ...