Specialist species have evolved to fill narrow niches but are especially susceptible to environmental change. With sufficient functional redundancy, ecosystem services can persist without specialists. Grooming behaviors are common in both terrestrial and aquatic organisms. However, in aquatic systems there is a heavy reliance on intraspecific mutualisms where specialist species groom or “clean” parasites off host fishes. Here, we sampled the gut contents of 709 fishes, representing 61 species and including both cleaner and non-cleaner fishes, to compare their consumption of gnathiid isopods, the most common fish ectoparasites. We found that cleaner fishes eat significantly more gnathiids, and eat them more frequently, compared to non-cleaner fishes. Our results highlight the importance of both dedicated and facultative cleaners as consumers of ectoparasites and show that their role cannot be supplanted by generalist consumers. Furthermore, we suggest that different cleaner species act as complementary rather than redundant specialists.