Fish 'changes colour to hunt prey'
A small Australian fish has shown itself to be a real wolf in sheep's clothing by changing colour to mimic its neighbours.
The dottyback takes on the appearance of other fish so that it can sneak up undetected and eat their young, scientists have discovered.
While mimicry is common in nature and practised by animals ranging from cuckoos to butterflies, this master of disguise takes it to a new level.
The coral reef fish is able to change colour in different ways to match whatever species it is hunting.
Different types of damselfish are one of its favourite targets.
Dr William Feeney, from Cambridge University's Department of Zoology, who co-led the study, said: "By changing colour to imitate local damselfish communities, dottybacks are able to overcome the predator avoidance behaviour in the juvenile fish they hunt.
" The dottyback behaviour is comparable to the 'wolf in sheep's clothing' scenario from Aesop's Fables, where distinguishing the predator from the harmless 'flock' becomes increasingly difficult when they look alike - allowing the dottyback to creep up on unsuspecting juvenile damselfish."
Dottybacks are generally solitary and highly territorial predators around eight centimetres in length.
While they can vary their colouration from pink to grey, the scientists focused on two colour "morphs" - yellow and brown - seen on reefs surrounding Lizard Island, off the north-east coast of Australia.
The area has damselfish that are both yellow and brown.
To test the dottyback's colour changing ability, the scientists built their own artificial reef outcrops and populated them with either of the damselfish varieties.
When released among damselfish of the opposite colour, the dottybacks would change from yellow to brown or vice versa over a period of about two weeks.
Anatomical studies revealed changes at the cellular level in the dottyback's skin. The ratio of yellow to black pigment cells shifted to achieve the colour switch.
Once the dottyback matched the colour of the damselfish, they were up to three times more successful at capturing prey, the scientists found.
In addition, the fish changed colour to blend into their surroundings and hide from larger predators, such as the coral trout.
Damselfish also have an ability to camouflage themselves against their background by changing colour.
Dr Feeney added: "While the dottybacks change colour to aggressively mimic damselfish, they may also gain a secondary benefit: a reduced risk of being eaten themselves.
"Damselfish have evolved to blend into their environment, so, by imitating the damselfish, they also colour-match the habitat - making it harder for coral trout to see them.
"This is the first time that an animal has been found to be able to morph between different guises in order to deceive different species, making the dottyback a pretty crafty little fish."
The research is published in the journal Current Biology.