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 cleaners 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 cleaning behaviour of the Mediterranean cleaner wrasse Symphodus melanocercus, based on observations, cleaner gut contents, client ectoparasites and mucus 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 client ectoparasite load, it was also significantly linked to client mucus load, which would indicate that the cleaning behaviour of S. melanocercus is not purely altruistic. Finally, as client visit to cleaning stations is related to their ectoparasitism, we propose that ectoparasite removal is likely to be a benefit for the client fishes of S. melanocercus. Received: 28 July 2000 / Accepted: 8 November 2000