Importance of ectoparasites and mucus in cleaning interactions in the Mediterranean cleaner wrasse Symphodus melanocercus

In fish cleaning associations, the net benefits gained by clients and clean ers from cleaning have still not been clearly evaluated. In particular, the role of ectoparasitism and the importance of client mucus characteristics remain unclear for most cleaner fish species. This paper investigates the c leaning behaviour of the Mediterranean cleaner wrasse Symphodus melanocerus , based on observations, cleaner gut contents, client ectoparasites and muc us characteristics. We showed that this fish is a specialised cleaner fish, similar to some other tropical cleaner species. Gnathiid isopod larvae and caligid copepods represented a large proportion of the items preyed on by S. melanocercus. Although their feeding activity was related to their clien t ectoparasite load, it was also significantly linked to client mucus lend, which would indicate that the cleaning behaviour of S. melanocercus is not purely altruistic. Finally, as client visit to cleaning stations is relate d to their ectoparasitism, we propose that ectoparasite removal is likely t o be a benefit for the client fishes of S. melanocercus.