Host specificity of monogenean ectoparasites on fish skin and gills assessed by a metabarcoding approach.

Monogeneans are highly diverse fish ectoparasites with a direct life cycle, widely distributed, and are known to generally display strict host specificity. Factors related to the hosts and the parasite have been suggested to explain this high specificity. Monogeneans have also been observed to colonise fish species not in their natural host range under experimental conditions. We developed a specific metabarcoding protocol and applied it on the Sparidae-Lamellodiscus host-parasite system, to assess parasite diversity on skin and gills of several sparid host species. We first demonstrated that the use of a metabarcoding approach provided a better understanding of the diversity of monogeneans associated with teleost skin and gills than traditional approaches based on morphological identification. We identified a high diversity of both expected and unexpected (never observed on this host species) Lamellodiscus spp. on each host species and on skin and gills. No significant difference in parasite diversity was found between skin and gills. These results suggest that the establishment of the observed host specificity in monogeneans relies on multiple levels of regulation, involving the survival capacity of the larvae and host recognition mechanisms.