Morphological and molecular characterization of Hysterothylacium larval morphotypes (Nematoda: Raphidascarididae) infecting edible marine fish in the Black Sea

The morphological and molecular identification of Hysterothylacium larval morphotypes in the Black Sea remains unresolved and incomplete. The aim of current study was to provide a detailed morphological identification with rDNA whole ITS (ITS‒1, 5.8S subunit, ITS‒2) and mtDNA cox2 sequences data of Hysterothylacium larval morphotypes infecting four commonly edible marine fish species, including European anchovy, Engraulis encrasicolus (L.), horse mackerel, Trachurus trachurus (L.), whiting, Merlangius merlangus (L.), and red mullet, Mullus barbatus ponticus (E.) in the Black Sea (FAO fishing area 37.4.2). Hysterothylacium larval morphotypes were morphologically classified, followed by whole ITS and cox2 sequencing. Four Hysterothylacium larval morphotypes, III, IV, VIII, and IX, are described based on morphological and molecular data. The present study provides the first study reporting whole ITS and cox2 sequences for Hysterothylacium larval morphotypes III, IV, VIII and III, IV, VIII, IX, respectively, in the Black Sea. Here, we offer a foundation for future research on the distribution, morphologic and molecular identification of Hysterothylacium larval morphotypes infecting edible some marine fish in the Black Sea.

Characterization of ecto- and endoparasite communities of wild Mediterranean teleosts by a metabarcoding approach

Next-generation sequencing methods are increasingly used to identify eukaryotic, unicellular and multicellular symbiont communities within hosts. In this study, we analyzed the non-specific reads obtained during a metabarcoding survey of the bacterial communities associated to three different tissues collected from 13 wild Mediterranean teleost fish species. In total, 30 eukaryotic genera were identified as putative parasites of teleosts, associated to skin mucus, gills mucus and intestine: 2 ascomycetes, 4 arthropods, 2 cnidarians, 7 nematodes, 10 platyhelminthes, 4 apicomplexans, 1 ciliate as well as one order in dinoflagellates (Syndiniales). These results highlighted that (1) the metabarcoding approach was able to uncover a large spectrum of symbiotic organisms associated to the fish species studied, (2) symbionts not yet identified in several teleost species were putatively present, (3) the parasitic diversity differed markedly across host species and (4) in most cases, the distribution of known parasitic genera within tissues is in accordance with the literature. The current work illustrates the large insights that can be gained by making maximum use of data from a metabarcoding approach.