Feb 09, 2019 (dailymail.co.uk) - Fish may not be as stupid as they appear, as a study suggests they can recognise themselves in a mirror.
However cleaner wrasse fish have shocked scientists by suggesting they may have the same capability despite their tiny brains.
When shown a mirror, they appeared to notice coloured marks on their heads, which they then tried to scrape away on rocks and gravel in their tank.
Dr Alex Jordan, who led the study from the Max Planck Institute for Ornithology and Osaka City University in Japan, said: 'The behaviours we observe leave little doubt that this fish behaviourally fulfils all criteria of the mirror test as originally laid out.
'What is less clear is whether these behaviours should be considered as evidence that fish are self-aware-even though in the past these same behaviours have been interpreted as self-awareness in so many other animals.'
Cleaner wrasse live in tropical coral reefs and serve a useful purpose in cleaning parasites off larger fish.
To see if they could recognise their mirror image, scientists injected small amounts of brown dye into their throats and heads to look like a parasite.
The fish only attempted to remove the mark after seeing it in a mirror.
To check they knew it was themselves in the mirror, researchers presented them with an identical fish with the same mark seen through a clear divider.
The fish stopped trying to remove the mark on their own body, showing they were not fooled.
Cleaner wrasse almost never swim upside down but some did this 36 times in an hour in front of a mirror, suggesting they were watching their reflection.
They moved so they could better see the marks on their faces and also behaved aggressively towards the reflective surface.
The fish therefore satisfied every test for self-awareness, although experts remain sceptical.
