Fishes are constantly subjected to parasitic attack, pathogenic infections and associated injury. How fishes respond to these challenges often influences their survival. Infected and/or injured fishes may engage in behaviours that mitigate parasite loads and promote wound healing. Behaviours range from attempts to dislodge parasites against hard substrates, migrations to actively alter the osmotic environment, or complex cleaning interactions with specialist ‘cleaners’. We estimated that global cleaner diversity comprises 207 cleaner fish (from 106 genera representing 36 families) and 51 cleaner shrimp (from 11 genera representing six families). Experiments in aquaria showed that cleaner shrimp clean during the day and night, whereas cleaner fish are strictly diurnal in their cleaning, which permits a resurgence of parasite abundance on ‘cleaned’ host fishes the following night. Cleaner shrimp also reduced the infection pressure of a parasitic monogenean flatworm by eating the parasite’s benthic eggs and free-swimming infective larvae, implying that scavenging behaviour by shrimp has the potential to remove parasite life stages on substrates and in the water column. Moreover, cleaner shrimp masticate parasite eggs, larvae and adults and render them non-viable whereas parasite eggs can pass through the intestinal tracts of cleaner fish unabated in their capacity to hatch. Although cleaner fish are believed to support wound healing on injured fish clients in the wild, cleaner shrimp may aggravate injuries opportunistically on fish in aquaria, indicating that client fish may actively regulate these interactions. The diversity of species that engage in cleaning symbiosis and the varied regulatory behaviours offered by cleaner fish and shrimp offer substantial value to the fitness of client fishes and may be vital to temperate and tropical reef diversity.