Does cleanerfish service quality depend on client value or choice options?

Cleaning fish mutualisms appear to be good examples of biological markets. Two classes of traders exist: cleaner fish and their fish clients, each of which supplies a commodity required by the other (ectoparasite removal and a meal, respectively). However, clients are not all treated similarly by cleaners. There is evidence that clients with choice options (with potential access to more than one cleaner) have priority of access over clients without choice options. Market theory predicts that client value (i.e. ectoparasite load) should also influence cleaning service quality. We examined the relative roles of client choice options and client value in determining the duration of cleaning interactions between bluestreak cleaner wrasse, <i>Labroides dimidiatus</i>, and their clients across three geographically distant sites. We found a lack of covariation between client choice options and gnathiid ectoparasite loads. Geographical differences in gnathiid availability altered the importance of client gnathiid load as a determinant of client inspection duration. As predicted, clients with both choice options and high gnathiid loads were inspected for longer, but this was observed only in an area with a relatively high incidence of parasitism. These correlational results suggest that the importance of client choice for aspects of cleaner fish service quality may be modulated by parasite availability.