Abstract

A total of 61 specimens of deep-sea chimaeras (Hydrolagus melanophasma = 41; Chimaera sp. = 20) were obtained during September 2017 as by-catch of the local fishery of the Patagonian toothfish (Dissostichus eleginoides, Pisces: Nototheniidae) along the northern Chilean coasts (?22°20? S) at depths ranging from 950 to 1500 m using a deep-sea longline. Nine species of metazoan parasites were found in H. melanophasma and seven in Chimaera sp. Four species were shared between both host species. Gyrocotyle sp.1 (Cestodaria) and Multicalyx elegans (Aspidogastrea) showed the higher prevalence H. melanophasma (68.3% and 65.38%, respectively), whereas Plectognathotrema hydrolagi (Digenea), Gyrocotyle sp.1 (Cestodaria), and Chimaericola sp. (Monogenea) showed higher prevalence in Chimaera sp. (90%, 55% and 55%, respectively). Beta diversity analysis reveals that the parasite communities of these two related and sympatric species are strongly differentiated. Our results suggest a strong relationship between the ancient Holocephali, which harbor ancient parasites belonging to Rugogasteridae and Multicalycidae (Aspidogastrea), and two Cestodaria species. Chimaera spp. are also parasitized by some highly specific monogeneans, such as Chimaericola spp. Our results demonstrate the differences in the parasite community structures—both of ecto- and endoparasites—of two related and sympatric hosts. © 2025 by the authors.