Male cleaner wrasse punish cheating females

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Good customer service is everything to male cleaner wrasse (Labroides dimidiatus), according to research by scientists from the UK, Switzerland, and Australia published in a recent issue of the journal Science.

Nichola Raihani, Alexandra Grutter and Redouan Bshary have found that male cleaner wrasse appearing to aggressively protect the interests of the client by punishing cheating female fish are in fact after a decent meal.  

Cleaner wrasses eat ectoparasites off client fish, but sometimes resort to cheating by biting a chunk of mucus out of the client fish instead.  

When they do that, the disgruntled client fish frequently leave, leaving the wrasse without a meal.

The authors found that male cleaner fish working in male-female pairs would punish female fish that cheat (by aggressively chasing them) in order to protect their food source.  

The researchers conducted experiments in which working pairs of cleaner wrasse were trained to feed off model clients (Plexiglas plates) containing two food types: preferred prawn and less-preferred fish flake.

Eating prawn corresponded to cheating the client by eating mucus, whereas eating flake corresponded to cooperating by removing ectoparasites.  Whenever a fish ate prawn, the Plexiglas plate was removed.  

The authors found that male fish chased female fish more often if the behaviour of the females resulted in plate removal, and that female fish were less likely to cheat (eat prawn) after being chased by the male.

It is thought that the main benefit to the male by behaving this way (even though the main victims are the client fish) is to increase feeding opportunities.  

The authors hypothesise that “he establishment of self-serving third-party punishment in response to personal losses may be a key step toward third-party punishment without current involvement as in humans.”

For more information, see the paper: Raihani, NJ, AS Grutter and R Bshary (2010) Punishers benefit from third-party punishment in fish. Science 327, p. 171.