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Simple Summary: This research represents the first analysis of the population genetics of the diplectanid monogenean Lamellodiscus echeneis, sampled from wild and cage-reared gilthead seabream Sparus aurata across fifteen locations in the Southern (Tunisia) and Northern (Italy and Spain) regions of the Mediterranean Sea. The comparison of the newly obtained dataset to previously published sequences of L. echeneis, and the phylogenetic trees based on the analysis of ITS rDNA, confirmed the presence of only one species in the Mediterranean Sea. The star-like haplotype network inferred by COI sequences suggested a recent population expansion of L. echeneis. This study provides insights into the genetic variation among L. echeneis populations and did not reveal a clear genetic structure throughout Tunisian, Italian, and Spanish localities, possibly due to significant gene flow between the populations facilitated by the dispersion potential of hosts. The diplectanid monogenean Lamellodiscus echeneis (Wagener, 1857) is a specific and common gill parasite of the gilthead seabream Sparus aurata Linnaeus, 1758, in the Mediterranean Sea. Few isolated molecular studies of this monogenean have been conducted, and its population structure and genetic diversity are poorly understood. This study represents the first analysis of the population genetics of L. echeneis, isolated from wild and cage-reared gilthead seabream from fifteen localities in both the Southern (Tunisia) and Northern (Italy and Spain) regions of the Mediterranean Sea, using nuclear ITS rDNA markers and a partial fragment of the mitochondrial gene cytochrome oxidase subunit I (COI). The phylogenetic trees based on the newly obtained dataset and the previously published sequences of L. echeneis corroborated the spread of only a single species throughout the Mediterranean Sea. The star-like haplotypes network, inferred by COI sequences, suggested a recent population expansion of L. echeneis. This is supported by the observed high haplotype diversity (Hd = 0.918) and low nucleotide diversity (Pi = 0.01595). Population structure-based AMOVA for two groups (the Adriatic Sea and the rest of the Mediterranean Sea) attributed 35.39% of the total variation to differences within populations, 16.63% to differences among populations within groups, and 47.99% to differences among groups. Fixation indices were significant, with a high FST value (0.64612), likely related to the divergence of the parasite populations from the Adriatic Sea and other Mediterranean regions. Phylogenetic analyses grouped all samples into the main clade corresponding to L. echeneis from several localities. This study provides insight into the genetic variation between L. echeneis populations, and did not show a clear genetic structure between populations of L. echeneis throughout Tunisian, Italian, and Spanish localities, which can be attributed to the considerable gene flow between the populations favoured by the potential for host dispersion within the Mediterranean Sea. Finally, haplotypes shared between wild and cage-reared hosts provided evidence for the potential for cross-infection between wild and farmed hosts in the Mediterranean Sea. [ABSTRACT FROM AUTHOR]

Sharks belong to the most primitive group of jawed vertebrates and have some special structural and functional features such as a cartilaginous skeleton, a spiral intestinal valve, and a rectal gland for osmoregulation. In January 2020, ten specimens of Galeus melastomus, the Blackmouth catshark, were collected from the Gulf of Asinara (North Sardinia, Italy) and the entire alimentary canal was studied using histochemical reactions to characterize the mucous cell types. In the alimentary canal of G. melastomus, mucous cells mainly secrete a mixture of acidic and neutral mucins. Of the acidic mucins, only the carboxylated type was present in mucous cells of the stomach, while the sulfated type predominated in the esophagus and the intestines. The use of lectins revealed a distribution of sugar residues in mucins related to cellular activities of the different regions of the catshark alimentary canal. The current study is the first report to characterize the intestinal mucous cells of G. melastomus and to provide quantitative data on their different populations in the alimentary canal. [ABSTRACT FROM AUTHOR]

Simple Summary: Parasitic diseases represent a common issue in fish and, when histozoic forms are present, this elicits a chronic inflammatory reaction leading to granuloma formation. Despite the large knowledge of granuloma formation due to parasites in visceral organs, little is known about the development and the evolutive stages of granulomas in naturally infected fish. Mullets (Osteichthyes: Mugilidae) are a widespread euryhaline fish species that harbor different parasites, thus representing a suitable model for the study of parasite-induced granulomas. Combining histopathology and immunohistochemical tools, we identified three developmental granuloma stages (pre-granuloma, intermediate, and late stage), that ranged from an intact parasite with mild signs of tissue reaction to the formation of a structured granuloma. The identified histological patterns could be reliable tools in the staging of the granulomatous response associated with histozoic parasites and are an attempt to broaden the knowledge of the inflammatory response in different host–parasite systems. Histozoic parasite–fish host interaction is a dynamic process that leads to the formation of a granuloma, a specific chronic inflammatory response with discernible histological features. Mullets (Osteichthyes: Mugilidae) represent a suitable model concerning the development of such lesions in the host–parasite interface. The present work aimed to identify granuloma developmental stages from the early to the late phase of the infection and to characterize the immune cells and non-inflammatory components of the granuloma in different stages. For this purpose, 239 mullets were collected from 4 Sardinian lagoons, and several organs were examined by combining histopathological, bacteriological, and immunohistochemical methods. Granulomas associated with trematode metacercariae and myxozoan parasites were classified into three developmental stages: (1) pre-granuloma stage, characterized by intact encysted parasite and with no or mild tissue reaction; (2) intermediate stage, with partially degenerated parasites, necrosis, and a moderate number of epithelioid cells (ECs); and (3) late stage, with a necrotic core and no detectable parasite with a high number of ECs and fibroblasts. The three-tier staging and the proposed morphological diagnosis make it conceivable that histopathology could be an essential tool to evaluate the granulomas associated with histozoic parasitic infection in fish. [ABSTRACT FROM AUTHOR]

Simple Summary: The present study aimed to determine the praziquantel concentration in Sparus aurata muscle after oral administration of medicated feed. The in-feed treatment is commonly used in aquaculture breeding because it allows the treatment of a large fish population without stress. However, no residue limit exists for praziquantel in fish for human consumption, so the purpose of this work was to verify if this drug was able to accumulate in fish tissues after this treatment. The high-sensitivity analytical method developed in this work permitted to identify and quantify low concentrations of the drug in gilthead sea bream muscle, after the above-mentioned treatment. This method can be useful to competent authorities in evaluating the appropriate withdrawal time in fish treated with praziquantel and intended for human consumption. Praziquantel (PZQ) is an anthelmintic drug used in humans and animals against Platyhelminthes and in aquaculture in the Far East. Medicated feed is one of the most convenient forms of oral administration of drugs in aquaculture because it allows to treat a large population of fish in an easy way. However, this treatment may lead to residues in fish intended for human consumption. In this study, a liquid chromatography with tandem mass spectrometry (LC-MS/MS) method was developed in order to verify the presence of PZQ in samples of Sparus aurata after oral administration of feed treated with PZQ. The method was validated according to international guidelines. It showed good recoveries, selectivity and sensitivity (LOD and LOQ were 3.0 and 9.3 ng/g, respectively), with precision and matrix effect values ≤ 15%. This method could also be applied to determine PZQ residue in other fish species and thus to evaluate the appropriate withdrawal time in treated fish intended for human consumption. [ABSTRACT FROM AUTHOR]