For a tiny fish, the bluestreak cleaner wrasse has raised a big ruckus in the animal world.

Key points: The mirror tests whether a non-human animal can identify a mark on their body by looking in a mirror, while touching their body, not the mirror

The mirror tests whether a non-human animal can identify a mark on their body by looking in a mirror, while touching their body, not the mirror Until now only apes, elephants, dolphins and northern hemisphere species of magpie have passed the test

Until now only apes, elephants, dolphins and northern hemisphere species of magpie have passed the test The fish study opens a debate about whether the test is an appropriate gauge of animal awareness and whether we underestimate the ability of animals that do not pass this test

It is the first fish to pass the mirror test — a classic experiment used to assess the ability of a non-human animal to recognise itself — according to a study published today.

That puts it in the league of a handful of animals including apes, elephants, dolphins and the Eurasian magpie that have passed the test since it was first conceived 50 years ago.

The findings, published in the journal PLOS Biology, have opened a fierce debate: is the fish really self-aware or is the test a poor measure of animal smarts?

The study's senior author, Australian scientist Alex Jordan, believes the fish did recognise themselves in the mirror.

But, he said, the act of seeing a reflection doesn't necessarily equate to higher levels of consciousness and he questioned using the test to define the trait across the entire animal kingdom.

"For a long time this test was a sort of gatekeeper to a special club of 'smart animals'," Dr Jordan said.

"This is silly, as not all animals will respond to the test in a way we can interpret. To then suggest these animals are stupid is misleading.

"If we want to know how smart animals are, we must ask them in ways they care to respond to."

Fish in the mirror

The mirror test was developed in 1970 to test the ability of chimpanzees to use a mirror to identify themselves and examine marks drawn on their bodies that couldn't be directly viewed.

The idea is rather than reaching in to the mirror to manipulate the dot, they try to manipulate it on themselves, explained Culum Brown, an animal behaviour researcher at Macquarie University, who was not involved in the study.

"That's the point you realise they think they are looking at themselves in the mirror, not some other animal," Professor Brown said.

While some animals have passed the test, the evidence is less convincing for others, such as macaque monkeys, manta rays and parrots.

Curious to see if it worked on fish, Dr Jordan and his colleagues put a group of African cichlids — a diverse group of highly social and intelligent saltwater fish — to the test. They failed.

"We therefore wanted to test a fish which should care about a mark, is social, and is intelligent. And bingo, the cleaner wrasse fits the bill," said Dr Jordan, who is based at the Max Planck Institute for Ornithology in Germany.

Bluestreak cleaner wrasse cosied up to their reflection in a mirror. ( Supplied: Alex Jordan )

Labroides dimidiatus hang out on coral reefs obsessively picking away at parasites and dead skin on any fish, marine creature or diver that should happen by.

Dr Jordan and colleagues plonked 10 fish in an aquarium with a covered mirror. Nothing happened.

But, when they removed the covers, seven of the fish went into fight mode and exhibited behaviour such as swimming upside down, which had never been seen before in this species.

After a week they settled down and spent more and more time cosying up to the mirror, checking out their reflection.

The researchers stepped up the experiment by injecting coloured marks and invisible sham marks under the fish's skin in areas that could only be seen in the mirror.

The fish tried to scrape the coloured mark off when there was a mirror, but they did not react to the sham mark at all, or the coloured mark when there was no mirror.

So did it really pass the test?

Unlike many other animals that have passed this test, fish have a distinct disadvantage: they don't have arms, legs, trunks or beaks to point to the marks, which makes their actions harder to interpret.

But all the behaviours exhibited by the fish met the criteria of the test, Dr Jordan said.

"If I had described these behaviours to you, but let you guess that I was [talking about] a mammal, I don't think you would be resistant to the idea that this comprised evidence of passing the test.

"It is only when we say that this was a fish doing these things that we run into trouble," Dr Jordan said of the perception of some that fish would not be capable of these behaviours.

Professor Brown, who studies fish, agreed.

"When they did it for dolphins everyone just went 'Oh, yeah, dolphins, they're pretty smart', nobody really questioned it.

"But if you show something in fishes everyone goes 'What? Wait a minute'," Professor Brown said.

"I think it's pretty convincing the animal does know it's looking at itself in the mirror. Now the question is 'Does that mean it's some higher order intelligence of self awareness?' Well maybe, maybe not."

Loading...

But others, such as primatologist Frans de Waal of Emory University, were less convinced.

"It's very well possible these fish are doing the self-scraping because they connect the mirror image with themselves, but it is less convincing than the self-touching we see in the primates [apes]," Professor de Waal said.

He also noted that as it is impossible to draw a spot on a fish, the injection of dye under their skin may have provided sensory cues.

This would place fish on a similar level to macaque monkeys, which do not respond to visual marks alone, he commented in a separate piece in PLOS Biology.

"The monkey studies that we've done show its the combination between the visual mark and the sensation that gives them a leg up."

"They did control for sensation itself but they did not control for the combination because they could not do that."

Dr Jordan agreed the combination of the visual and sensory cues could have increased the reaction, but it did not invalidate the findings.

"Whether we learn that a reflection is of us through visual cues alone, or through visual and auditory, olfactory, or tactile cues as well, does not change the fact we are recognising ourselves," Dr Jordan said.

Professor Brown concurred.

"We already know that fish can use chemical self recognition, so they can recognise themselves using smell," he said.

Animal consciousness is not black and white

Scientists have long debated about whether or not the mirror test was an appropriate gauge of awareness.

Professor de Waal said the fish study would open up a new discussion about finding better ways to assess these traits across the animal kingdom.

The view that animals either have self awareness or they don't have self awareness is a "very black and white view of the animal kingdom," Professor de Waal said.

Loading...

"My feeling is that all animals need to know self concept, all animals need to know their place in the world.

"We need to design tests that give us a feel for the whole spectrum that exists."

Dr Jordan agreed.

"If we want to understand the complexity of life, and our place within that complexity, we must ask questions in a way that avoids the inherent bias we as narcissistic humans have."