Trending Science: Can fish recognise themselves in the mirror?

It’s no secret that fish have poor memories, and because of this they’re perceived as low on the animal IQ scale. Recent findings suggest that fish may be smarter than we think.

According to research published in the journal ‘PLOS Biology’ small tropical reef fish called cleaner wrasse can pass a standard test of recognising themselves in a mirror despite their tiny brains. Introduced in 1970 and considered the gold standard for animal intelligence the so-called mirror test is designed to demonstrate self-awareness.

Are fish self-aware?

“These fish are fascinating in their breadth of cognitive abilities – and underappreciated” Dr Alex Jordan senior author and evolutionary biologist at Germany’s Max Planck Institute for Ornithology told the British newspaper ‘The Guardian’.

Researchers from the Max Planck Institute and Japan’s Osaka City University injected small amounts of brown dye into cleaner wrasse’s throats and heads to look like a parasite. This was done to see if they could recognise their mirror image. The fish only tried to get rid of the mark after seeing it in a mirror. Then, the team presented them with an identical fish with the same mark seen through a clear divider to check they knew it was themselves in the mirror. The fish weren’t fooled because they stopped trying to remove the mark on their own body. Cleaner wrasse aren’t known for swimming upside down, but some did this 36 times in an hour in front of a mirror. This suggests they were watching their reflection. The fish moved so they could better see the marks on their faces. They also behaved aggressively towards the reflective surface.

The 10 or so cleaner wrasse passed the test. The research team concluded that fish might have much higher cognitive abilities than previously thought. The fish “shows behaviors during the mirror test that are accepted as evidence for self-awareness in many other species” Dr Jordan told ‘Reuters’.

Where exactly do fish belong on the animal intelligence scale?

To date, several animals have passed the test. They include great apes, Asian elephants, bottlenose dolphins, orca whales and Eurasian magpies. Humans do so at around 18 months old.

However, Dr Jordan believes the fish could have succeeded without possessing true self-awareness. He wonders if the test represents a dependable measure of animal cognitive abilities. “I don’t claim that fish lack self-awareness, but rather that the minimal required explanation for the behaviors we observe in the mirror test does not require invocation of self-awareness, self-consciousness, or theory of mind.”

“What if self-awareness develops like an onion building layer upon layer rather than appearing all at once?” asked Dr Frans de Waal a leading primatologist at Emory University in the United States in a follow-up article commissioned by ‘PLOS Biology’. Dr de Waal who has studied mirror self-recognition in mammals added that “to explore self-awareness further we should stop looking at responses to the mirror as the litmus test. … Only with a richer theory of the self and a larger test battery will we be able to determine all of the various levels of self-awareness including where exactly fish fit in.”