Scientists say some fish can recognise themselves in the mirror, the ability of which has used for decades as a gold standard measure of animal intelligence.
Passing the test is widely viewed as an indication of self-awareness and until now, the only animals to have crossed this threshold are great apes, bottlenose dolphins, killer whales, Eurasian magpies and a single Asian elephant.
But now, the cleaner wrasse may have joined the club. Labroides dimidiatus lives in coral reefs and the species has complex social lives, forming allegiances and enemies, making logical inferences about whether they will beat other fish in fights and showing a capacity for deception.
The fish live in mutually beneficial partnerships with larger client fish from whom they feed on dead skin and parasites.
During the mirror test, the researchers placed a mark on the fish in a location that could only be seen in a mirror reflection.
Initially, the fish reacted aggressively and repeatedly tried to bite their reflections. But over the next few days, they stopped biting and started “behaving weirdly” in front of the mirror, swimming upside down, for instance, or doing repeated bursts of acceleration past the mirror.
The findings are published in the journal PLOS Biology.