The evolution of cleaner fish signals poses an interesting question: Which came first, cleaning behavior or signal coloration? Our study implies that perhaps cleaning behavior evolved first and signal coloration then followed as cleaners benefited from attracting more clients to cleaning stations based on their coloration. Facultative cleaners are often missing lateral stripes or a blue or yellow coloration (Table S1) but are still able to gain some of their dietary requirements from cleaning [1]. A subterminal mouth and small body size have also been suggested as prerequisites for cleaning 1 and 2; these features may enable cleaners to approach and remove ectoparasites from larger host fish.