Are cleaning interactions offered by large cleaners positive?

ABSTRACT Cleaning symbiosis is a cooperative interspecific interaction among reef fishes that helps to maintain healthy marine communities. Despite its importance, our knowledge on the cleaner role of many species, and on the costs and benefits of these interactions, is still scarce. Here, we report for the first time an adult Guinean angelfish Holacanthus africanus acting as cleaner of the smaller client blackbar soldierfish Myripristis jacobus in the remote Cabo Verde Archipelago, Eastern Atlantic. Adult angelfish cleaning behaviour is a rare juvenile trait retention, which based on our observations could have a negative effect on smaller clients. This negative effect can be associated with the fish’s extra lower jaw joint, adapted to extract sessile invertebrates from the substrate, which can remove the client’s tissues during the cleaning attempt. Thus, although cleaning interactions have been viewed as examples of marine mutualisms, the costs and benefits of cleaning for cleaners and clients require more studies. Our study also builds on the scarce information on cleaning behaviour of adult fishes and offers highlights on this symbiosis in isolated locations with low species richness and absence of dedicated cleaners.