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Simple Summary: Mercury represent a serious threat for marine ecosystems due to its persistence in the environment. Fishes are the most numerous and widely distributed group of vertebrates, living in the sea with different species often studied and used as bioindicators of the quality of aquatic systems being able to reflect even small changes in environmental parameters. Mitochondria are small cell organelles with their own DNA and the number of mitochondria within a cell is highly variable in different animal tissues, depending on metabolic requirements. Mitochondrial genome is vulnerable to reactive oxygen species (ROS) which in turn impair mitochondrial function. Therefore, the aim of the present study was the validation of the variation in the number of mitochondrial DNA copies (mtDNAcn) as biomarker of oxidative stress in aquatic environment. Three selected fish species were collected in Augusta Bay, a contaminated area remarkable by past Hg inputs, and in a control area (Marzamemi and Portopalo di Capo Passero), both in the South-East of Sicily. Based on the evidence found, the assessment of mtDNAcn variation emerges as a valid biomarker of oxidative stress deriving from contaminant exposure. Mercury (Hg) pro-oxidant role on biological systems and its biogeochemical cycle represent a serious threat due to its persistence in marine environment. As the mitochondrial genome is exposed to reactive oxygen species (ROS), the aim of the present study is the validation of the variation in the number of mitochondrial DNA copies (mtDNAcn) as biomarker of oxidative stress in aquatic environment. During summer 2021, three selected fish species (Mullus barbatus, Diplodus annularis and Pagellus erythrinus) were collected in Augusta Bay, one of the most Mediterranean contaminated areas remarkable by past Hg inputs, and in a control area, both in the south-east of Sicily. The relative mtDNAcn was evaluated by qPCR on specimens of each species from both sites, characterized respectively by higher and lower Hg bioaccumulation. M. barbatus and P. erythrinus collected in Augusta showed a dramatic mtDNAcn reduction compared to their control groups while D. annularis showed an incredible mtDNAcn rising suggesting a higher resilience of this species. These results align with the mitochondrial dynamics of fission and fusion triggered by environmental toxicants. In conclusion, we suggest the implementation of the mtDNAcn variation as a valid tool for the early warning stress-related impacts in aquatic system. [ABSTRACT FROM AUTHOR]

Simple Summary: Fishery products are an important part of the Mediterranean diet and constitute a high source of nutrients for consumers, contributing to the prevention of several health diseases. This work analysed the protein, amino acids, and fatty acids of Mediterranean target species (four fish species and one crustacean species) which are mostly consumed in Sicily. The nutritional composition of the selected species together with the evaluation of nutrient indices showed the high quality of the sampled fish. The excellent profile of the fatty acid of "blue fish" species highlights the opportunity for local people to benefit from a highly nutritional product originating from local and sustainable fisheries and with an affordable commercial value. The protein, essential amino acid, and fatty acid composition of European pilchard (Sardina pilchardus), European hake (Merluccius merluccius), surmullet (Mullus surmuletus), red mullet (Mullus barbatus), and deep water rose shrimp (Parapenaeus longirostris) from the central Mediterranean Sea were investigated. All the species showed an essential amino acid content of about 50% of total amino acids, while the protein and total fatty acids content varied from 19.9 to 24.8% and from 1.4 to 5.1%, respectively. The fatty acid profile mainly followed the order SFA (39.1–52.6%) > PUFA (21.0–39.3%) > MUFA (15.6–24.3%). Palmitic and stearic acids were predominant among saturated fatty acids (38–52% and 21–25%, respectively), while palmitoleic and oleic acids were the most represented of the total monounsaturated acids (10–21% and 55–68%, respectively). All the species, as expected, showed a more significant proportion of n-3 PUFA (EPA + DHA) of about 81–93% of the total PUFA, with the highest values was found in European pilchard. Also, several fat quality index values, such as n-6/n-3 ratio, PUFA/SFA, the index of atherogenicity (IA), the index of thrombogenicity (IT), the hypocholesterolemic/hypercholesterolemic ratio (HH), and fish lipid quality/flesh lipid quality (FLQ) were calculated to assess the nutritional quality. All the obtained results, along with the fat quality indexes, indicated the excellent nutritional values of the selected species. [ABSTRACT FROM AUTHOR]

Simple Summary: The old world killifish Aphanius fasciatus is a typical inhabitant of transition waters along the coasts of the central and eastern Mediterranean Sea, where it lives in environments (salt ponds, estuaries, and coastal lagoons) with large variations in salt, oxygen, and temperature. Therefore, A. fasciatus could be an interesting non-model species to be studied to evaluate the response of the mitochondrial oxidative phosphorylation (OXPHOS) genes to the variations and extremes of environmental factors. In this study, the sequences of three OXPHOS genes were analyzed in six populations of A. fasciatus to detect mutations and sites subject to selection. The results indicate that mutations were detected in two genes of the Greek population. Moreover, positively selected sites were also found. The information we obtained from the mitochondrial DNA sequences of A. fasciatus adds to the growing data on selective pressure acting on mitochondrial DNA. These results should be explored from the perspective of the local adaptation of a species highly tolerant to wide fluctuations of environmental parameters and should be supported using experimental evidence to better understand the interplay between historical climatic events and local adaptation and how each of them contributes to shaping the genetic structure of this species. Mitochondrial oxidative phosphorylation (OXPHOS) genes are a system subject to selection under determined environmental constraints despite a neutral evolution model that has long been hypothesized for the mitochondrial genome. In this study, the sequences of ND1, Cytb, and COI OXPHOS genes were analyzed in six populations of the eurythermal and euryhaline killifish A. fasciatus, to detect non-synonymous mutations leading to amino acid changes and to check whether selection acted on them using tests of recombination and selection. The results indicate a high COI and Cytb gene diversity and a high percentage of private haplotypes in all populations. In the Greek population, non-synonymous nucleotide substitutions were observed in the N-terminal region of COI and Cytb. Positively selected sites were also found. The information we obtained from the mitochondrial DNA sequences of A. fasciatus adds to the growing data on selective pressure acting on mitochondrial DNA in non-model species. These results should be explored from the perspective of the local adaptation of eurythermal and euryhaline species and supported using experimental evidence to better understand the interplay between historical climatic events and local adaptation and how each of them contributes to shaping the genetic structure of this species. [ABSTRACT FROM AUTHOR]

Simple Summary: Industrial activities significantly damage the surrounding environment due to the release of contaminants of various types. Therefore, the search for parameters that can provide information on the quality of the environment is of great relevance. In this research, for the first time, specimens belonging to Opsius heydeni, an insect living on Tamarix plants, were sampled and analyzed at two Sicilian sites (the polluted industrial site Priolo Gargallo and the control site Oasi del Simeto) to study the effect of pollution on wildlife organisms. Using molecular biology techniques, it has been seen that environmental pollutants can modify the mitochondrial DNA in these specimens; in particular, a decrease in the number of DNA molecules was observed in the specimens sampled at Priolo Gargallo. In conclusion, these results highlight how the studied species can be useful to monitor the effects of pollutants on biota. Mitochondrial DNA easily undergoes alterations due to exposure to stress factors. In particular, mitochondrial DNA copy number (mtDNAcn) variation can be used as a biomarker of the effect of exposure to various environmental contaminants. In this study, a molecular investigation based on the evaluation of mtDNAcn variation was applied for the first time to individuals belonging to the species Opsius heydeni. A total of 20 samples were collected from two sites in eastern Sicily: Priolo Gargallo, a site with a strong anthropic impact, and the Simeto river Oasis, a control site. Specimens identified based on morphological traits were used to obtain COI gene sequences from this species that were not previously available in GenBank. After processing, the relative mtDNAcn was evaluated using real-time PCR of a portion of the COI and 18S genes. A decrease in the mtDNAcn in the specimens from the polluted site was observed. These results highlight how environmental contaminants can alter the mitochondrial genome and how Opsius heydeni can be considered a potential bioindicator species of environmental quality. [ABSTRACT FROM AUTHOR]

The DNA analysis is the best approach to authenticate species in seafood products and to unveil frauds based on species substitution. In this study, a molecular strategy coupling Cytochrome Oxidase I (COI) DNA barcoding with the consolidated methodology of Restriction Fragment Length Polymorphisms (RFLPs), named COIBar-RFLP, was applied for searching pattern of restriction enzyme digestion, useful to discriminate seven different fish species (juveniles of Engraulis encrasicolus and Sardina pilchardus sold in Italy as "bianchetto" and Aphia minuta sold as "rossetto"; icefish Neosalanx tangkahkeii; European perch, Perca fluviatilis and the Nile Perch, Lates niloticus; striped catfish, Pangasianodon hypophthalmus). A total of 30 fresh and frozen samples were processed for DNA barcoding, analyzed against a barcode library of COI sequences retrieved from GenBank, and validated for COIBar–RFLP analysis. Cases of misdescription were detected: 3 samples labeled as "bianchetto" were substituted by N. tangkahkeii (2 samples) and A. minuta (1 sample); 3 samples labeled as "persico reale" (P. fluviatilis) were substituted by L. niloticus and P. hypophthalmus. All species were simultaneously discriminated through the restriction pattern obtained with MspI enzyme. The results highlighted that the COIBar-RFLP could be an effective tool to authenticate fish in seafood products by responding to the emerging interest in molecular identification technologies. [ABSTRACT FROM AUTHOR]