Scientists believe that they have proven that fish are ‘self-aware’

by Steve Reynolds

Because of my interest in fish behaviour, and a desire to learn all about fish cleaning behaviour as a part of that, I was very interested to read a recent newspaper report regarding cleaner wrasse.

The report only featured in The Advertiser during February 2019, even though the topic had been reported online in August 2018.

The Advertiser of 9th February 2019 had a short report with the headline “Fishy tale of scaling IQ heights”. It went on to suggest that fish have a higher IQ than what we tend to give them credit for.

The report stated that scientists from the Max Planck Institute of Ornithology had established that fish can recognise themselves in mirrors. Cleaner wrasse surprised the researchers when they injected brown dye into the throats of the fish to see if the fish could recognise their reflection in a mirror.

If the fish were able to recognise their reflection in a mirror, they would have fulfilled “one of the primary tests of animal intelligence”.

They did just that! Rather than mistaking the dye for a parasite and trying to clean their reflection, the cleaner wrasse tried to scrape their body against rocks. This led the scientists to declare that the fish were ‘self-aware’.

I wanted to find out more about the study. An online search led me to the web page at , which carried the headline “Tiny fish passes mirror test, might be self-aware”.

The fish involved was identified as the Bluestreak Cleaner Wrasse, Labroides dimidiatus (shown above). The test conducted by the scientists at the Max Planck Institute of Ornithology is called the mirror self-recognition test (MSR). It was apparently first used by psychologist Gordon Gallup during the 1970s. Gallup presented the MSR to a group of adolescent chimpanzees. He concluded that a change in their behaviour required “some level of self-awareness, a mental model of their own body as distinct from friends, foes, or other parts of the environment”. The MSR then became a key tool for researchers studying animal self-recognition.

The team from the Max Planck Institute of Ornithology settled on Labroides dimidiatus for their experiment because it has good vision and an ability to spot parasites on other fish. Both of these attributes made it ideally suited for MSR-type tests.

Details of the tests are explained on the web page as follows: –

“The team placed 10 fish in individual tanks outfitted with a mirror. Being highly territorial animals, the fish at first attacked the mirrors, perceiving their reflection as intruders. Their attitude soon changed, however: within a few days, the fish were actually dancing in front of the mirrors, the team notes. This easily qualifies as ‘unusual’ behavior for the species, which tends to be solitary.

“Next, the researchers placed a spot of colored gel on eight of the fishes’ heads in a position where they’d only be visible in the mirror. Seven of the fish spent ‘significantly more’ time in positions where the gel was visible in their reflection, the team writes. Several of them went on to spend more time than before trying to scrape the area against objects in their environment, the researchers add.

“While the results suggest that the wrasse could perceive the images in the mirror as their own reflection, and the gel tests seem to indicate that they can notice outside changes to their bodies, the paper has sparked its own bout of debate. Some critics have pointed out that it’s possible the wrasse viewed the blobs as parasites on the skins of other fish, and not as being on their bodies at all.

“Should the findings be confirmed, however, it would be an exciting development. Wrasses have relatively simple nervous systems, and we tend to associate self-awareness with complex brains. Not only would it be exciting to see self-awareness develop on such restrained ‘hardware’, but also to understand what that difference means in terms of how the fish experience self-awareness.”

The web page also stated that the paper Cleaner wrasse pass the mark test. What are the implications for consciousness and self-awareness testing in animals? has been published in the preprint server bioRxiv.

The paper “Cleaner wrasse pass the mark test. What are the implications for consciousness and self-awareness testing in animals?” was written by Hatta Takashi, Tmohiro Takeyama, Satoshi Awata, Hirokazu Tanaka, Jun-ya Asai, Alex Jordan and it can be found at .

According to the paper’s abstract, “The ability to perceive and recognise a reflected mirror image as self (mirror self-recognition, MSR) is considered a hallmark of cognition across species. Although MSR has been reported in mammals and birds, it is not known to occur in any other major taxon. A factor potentially limiting the ability to test for MSR is that the established assay for MSR, the mark test, shows an interpretation bias towards animals with the dexterity (or limbs) required to touch a mark. Here, we show that the cleaner wrasse fish, Labroides dimidiatus, passes through all phases of the mark test: (i) social reactions towards the reflection, (ii) repeated idiosyncratic behaviours towards the mirror (contingency testing), and (iii) frequent observation of their reflection. When subsequently provided with a coloured tag, individuals attempt to remove the mark in the presence of a mirror but show no response towards transparent marks, or to coloured marks in the absence of a mirror. This remarkable finding presents a challenge to our interpretation of the mark test – do we accept that these behavioural responses in the mark test, which are taken as evidence of self-recognition in other species, mean that fish are self-aware? Or do we conclude that these behavioural patterns have a basis in a cognitive process other than self-recognition? If the former, what does this mean for our understanding of animal intelligence? If the latter, what does this mean for our application and interpretation of the mark test as a metric for animal cognitive abilities?”

By Steve Reynolds

Steve Reynolds is the current President of MLSSA and is a long-standing member of the Society. Steve was a keen diver, underwater explorer & photographer before illness struck. He is chief author of the Society's extensive back catalogue of newsletters and journals.

One thought on “Scientists believe that they have proven that fish are ‘self-aware’”
  1. The above line drawing of a cleaner wrasse was done by Katrina Bishop for my 1980 article “The Colour of Fish”, MARIA Journal Vol.1, No.5.

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