Diversity and community structure of ectoparasites infecting some elasmobranch species off the Tunisian coast

With more than 62 reported species, Tunisia has a rich diversity of elasmobranchs. However, investigations of their parasites in Tunisian waters remain rare and fragmented. With the global biodiversity crisis that most living species are facing, the study of parasite diversity is crucial for assessing ecosystem health and host-parasite interactions. In this study, 2,092 specimens of cartilaginous fishes (Chondrichthyes: Elasmobranchii) belonging to eight species, six genera and five families were sampled along the Tunisian coast and examined for their ectoparasites. The different host species were each infected by at least one ectoparasite species. A total of 24 ectoparasite species, among which three new species, were collected and identified. Copepods exhibited the highest taxonomic diversity (11 species), followed by 'monogeneans' (6 species), isopods (5 species), and leeches (2 species). To understand the diversification and specialisation of the collected ectoparasite species and the factors that may influence them, parasitological indices, parasitic communities' composition, parasitic richness and seasonal variation are presented in this work. Parasite community structure varied among host species and families. Mustelus mustelus (Linnaeus) showed the greatest diversity (Shannon-Wiener H' = 1.91; Species richness (SR) = 10), whereas Torpedo torpedo (Linnaeus) hosted only a single leech species. The present study demonstrates that parasite community composition and structure of the studied hosts seem to be influenced primarily by the geographic distribution, the sampling effort and the population density, along with other factors such as the phylogeny of the host species.