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Fish kills prey by posing as family

Press Trust of India  |  Melbourne 

A predatory fish in the Australian Great Barrier Reef preys on smaller fish by changing colour and pretending to be an adult of their species, scientists have found.

By changing colours, the dusky dottyback also decreases its risk of being detected by predators.

The dusky dottyback (Pseudochromis fuscus), a small predatory fish that is found throughout the Indo-Pacific, occurs in many different colourations and has the peculiar ability to change its body colouration.

Why dottybacks vary in colouration and why they are able to change their colour has long remained a secret.

An international research team led by evolutionary biologists Dr Fabio Cortesi and Professor Walter Salzburger from the University of Basel, has now been able to explain why dottybacks adopt different colours.

So far, it had been assumed that the colour variety is genetically determined, meaning that the different coloured dottybacks had likely adapted to their respective habitat background or that colouration was sexually determined.

The zoologists now show that dottybacks can actively change their colour in a relatively short amount of time.

Their goal: to mimic other fish species in their surroundings in order to prey on their juvenile offspring.

Researchers observed that dottybacks used a particularly clever approach to reduce the threat of being found out.

These fish change their colour to mimic different harmless fish species in their surroundings to prevent being recognised by their prey, the offspring of the mimicked fish.

"This strategy is very similar to the classic example of the wolf in sheep's clothing. However, while the wolf may be found out eventually, dottybacks are able to change their colouration, making it difficult for their prey to learn about the threat they impose," said first-author Dr Fabio Cortesi.

In addition, changing colour also provides a second benefit to the dottybacks - it also increases their ability to hide from predators.

The researchers trained bigger coral trout to strike at images of dottybacks in front of different backgrounds.

The experiment showed that coral trout struck significantly less often at the dottyback images that were colour-matched to the natural background of those fish mimicked by the dottyback.

The study was published in the journal Current Biology.

First Published: Fri, March 20 2015. 16:57 IST