title: Do cleaning organisms reduce the stress response of client reef fish?
abstract: BACKGROUND
  Marine cleaning interactions in which cleaner fish or shrimps remove parasites from visiting 'client' reef fish are a textbook example of mutualism. However, there is yet no conclusive evidence that cleaning organisms significantly improve the health of their clients. We tested the stress response of wild caught individuals of two client species, Chromis dimidiata and Pseudanthias squamipinnis, that had either access to a cleaner wrasse Labroides dimidiatus, or to cleaner shrimps Stenopus hispidus and Periclimenes longicarpus, or no access to cleaning organisms.
  
  
  RESULTS
  For both client species, we found an association between the presence of cleaner organisms and a reduction in the short term stress response of client fish to capture, transport and one hour confinement in small aquaria, as measured with cortisol levels.
  
  
  CONCLUSIONS
  It is conceivable that individuals who are more easily stressed than others pay a fitness cost in the long run. Thus, our data suggest that marine cleaning mutualisms are indeed mutualistic. More generally, measures of stress responses or basal levels may provide a useful tool to assess the impact of interspecific interactions on the partner species.
authors.affiliation: Department of Biology, University of Neuchâtel, Emile-Argand 11, 2009 Neuchâtel, Switzerland. redouan.bshary@unine.ch.
authors.forename: Redouan
authors.initials: R
authors.lastname: Bshary
authors.forename: Rui F
authors.initials: RF
authors.lastname: Oliveira
authors.forename: Tânia Sf
authors.initials: TS
authors.lastname: Oliveira
authors.forename: Adelino Vm
authors.initials: AV
authors.lastname: Canário