Wild fish and parasites: Mediterranean surveys

This doctoral thesis aims to provide original data on wild fish parasite fauna, to improve the current knowledge on teleost from the western and central Mediterranean Sea. The thesis is presented in the form of “thesis by publication” and is composed of three chapters. Chapter 1 aimed to investigate the parasite fauna of dusky grouper (E. marginatus) from the central Mediterranean Sea, between the provinces of Messina and Syracuse. In this chapter, two main targets, the economic value and the current lack of studies of the study area, were considered. In the study, 70 dusky groupers caught between 2018 and 2020 were included. Forty-seven specimens (67.2%) were positive for endo and ectoparasites: nematodes, digenean and monogenean trematodes. The most retrieved species was Prosorhynchus caudovatus (42.9%), followed by Podocotyle temensis (28.6%), Didymodiclinus sp. (18.6%), Philometra jordanoi (5.7%), and Anisakis Type II larvae (5.7%). The different prevalence, found between warm and cold seasons, is probably related to E. marginatus, characterized by molluscs that are considered as intermediate hosts for the retrieved parasite species. Chapter 2 provides a morphological and molecular characterization of a new species of Didymodiclinus (Trematoda: Didymozoidae) retrieved in Epinephelus marginatus (Teleostei: Serranidae) from Sicily and the island of Majorca. Between 1998 and 2020, 279 E. marginatus specimens were examined. The new species was morphologically different from the most similar congeneric species, retrieved in different hosts and locations within the host tissues, as described from other geographical areas. Moreover, this parasite represented the first didymozoid species reported in E. marginatus from the central and western Mediterranean Sea. For molecular evaluation, partial 28S, partial ITS-2 ribosomal RNA regions and mitochondrial COX1 gene were used. Comparison of Didymodiclinus marginati n.sp. sequences with other deposited sequences of 28S revealed that the new isolates cluster with several unidentified didymozoids. The morphological and genetic results obtained permitted to propose new identification keys for the genus Didymodiclinus. Chapter 3 describes a gastric granulomatous reaction caused by Anisakis pegreffii in yellowmouth barracuda (Sphyraena viridensis). In this study, 68 S.viridensis specimens were sampled from different fish markets on the east coast of Sicily. Retrieved parasite specimens and pathological tissues were collected for histological and molecular analyses. Twelve specimens (p=17.6%, MA=0.9, MI=4.8) were positive for nematode larvae, identified as Anisakis sp. One large female S. viridensis specimen showed massive parasite infection associated with multiple modular lesions of the gastric wall. Histological evaluation showed that the parasite body was surrounded by a granulomatous reaction made up of macrophages, epithelioid cells, some lymphocytes, and an external connective layer. Molecular analysis performed with 18S rRNA and cox2 genes allowed to identify the retrieved parasite larvae as A. pegreffii. The lesions described in the present chapter, although macroscopically identical to the human eosinophilic granuloma, microscopically showed significant variations in the involved inflammatory cell population, as in the host immune reaction.