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“Punisher” of the seas is a little finned janitor

Jan. 8, 2010
Courtesy Zoological Society of London 
and World Science staff

For small fish known as clean­er wrasse, step­ping into the line of fire reaps huge re­wards, ac­cord­ing to a new stu­dy.

Re­search­ers from the Zo­o­log­i­cal So­ci­e­ty of Lon­don, Uni­vers­ity of Queens­land, Aus­tral­ia and the Uni­vers­ity of Neu­châ­tel, Switz­er­land found that male clean­er wrasse are quick to play the he­ro when their din­ner is at stake.

Apair of clean­er wrasse, spe­cies La­broid­es di­mi­dia­tus, clean­ing an Achan­thu­rus mata cli­ent. (Im­age cour­te­sy of Ger­ry Al­len)


Clean­er wrasse live on cor­al reefs and feed on par­a­sites that live on the skin of much larg­er fish. These “clients” calmly let the clean­ers nib­ble at them in re­turn for the cleans­ing ben­e­fits.

Wrasse can get an even big­ger meal if they take some of the mu­cus off the skin of a cli­ent, but this “cheat­ing” re­sults in a dis­grun­tled cus­tom­er.

The sci­en­tists found that male wrasse will ag­gres­sively chase female wrasse who de­liv­er poor cus­tom­er serv­ice, seem­ingly pro­tect­ing the in­ter­ests of the cli­ent when in fact they’ve got their own stom­achs in mind.

“Clients will leave if they are cheated at a clean­ing sta­t­ion. That means the ma­le’s din­ner leaves if the female cheats,” said Nichola Rai­hani of the Zo­o­log­i­cal So­ci­e­ty, lead au­thor of the study pub­lished this week in the re­search jour­nal Sci­ence.

“By pun­ish­ing cheat­ing fema­les, the males are not really stick­ing up for the cli­ents but are mak­ing sure that they get a de­cent meal.”

This ten­den­cy to stick up for a vic­tim is some­thing that hu­mans are prone to, but no one really knows why we do it, Rai­hani not­ed. The study raises the pos­si­bil­ity that “Robin Hood” type be­hav­iour might be less char­i­ta­ble than we think.

The next stage of the re­search will con­cen­trate on the threat posed to male fish by si­m­i­lar sized females who can un­dergo sex changes and ul­ti­mately chal­lenge their au­thor­ity, Rai­hani and col­leagues said.


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For small fish known as cleaner wrasse, putting themselves in the line of fire reaps huge rewards, according to a new study. Researchers from the Zoological Society of London, University of Queensland, Australia and the University of Neuchâtel, Switzerland found that male cleaner wrasse are quick to play the hero when their dinner is at stake. Cleaner wrasse live on coral reefs and feed on parasites that live on the skin of much larger fish. The larger fish calmly let the cleaners nibble at them in return for the benefits. Wrasse can get an even bigger meal if they take some of the mucus off the skin of a client, but this “cheating” results in a disgruntled customer. The scientists found that male wrasse will aggressively chase females who deliver poor customer service, seemingly protecting the interests of the client when in fact they’ve got their own stomachs in mind. “Clients will leave if they are cheated at a cleaning station. That means the male’s dinner leaves if the female cheats,” said Nichola Raihani from the Zoological Society of London, lead author of the study published this week in the research journal Science. “By punishing cheating females, the males are not really sticking up for the clients but are making sure that they get a decent meal.” This tendency to stick up for a victim is something that humans are prone to, but no one really knows why we do it, Raihani noted. This study raises the possibility that ‘Robin Hood’ type behaviour might be less charitable than we think. The next stage of the research will concentrate on the threat posed to male fish by similar sized females who can undergo sex changes and ultimately challenge their authority, Raihani and colleagues said.