Assessment of health risks due to toxic metals in demersal fish captured from Saros and Edremit Bays, Northern Aegean Sea.

Bays are vulnerable ecosystems generally located near densely populated areas where toxic metals tend to accumulate and stay longer, affecting marine life. This study aimed to investigate the age-based health risks arising from Hg, Cd, Pb, and As in demersal fish captured from two major bays in the Aegean Sea. For this purpose, red mullet, whiting, piper gurnard, and tub gurnard, frequently consumed species, were caught from Saros and Edremit Bays. Toxic metal concentrations were determined from the muscle tissue of fish. Health risk assessments were conducted by the estimation of weekly intake (EWI), provisional tolerable weekly intake (PTWI), target hazard quotient (THQ), total THQ (TTHQ), and target carcinogenic risk (TR). Red mullet from Edremit Bay was the species with the highest toxic metal levels, which were 1.597 mg/kg, 0.041 mg/kg, 0.070 mg/kg, and 19.351 mg/kg for Hg, Cd, Pb, and As, respectively. Whiting from Edremit Bay had higher mean concentrations of Hg and As than those from Saros Bay. The levels of Hg, Pb, and As (0.328, 0.043, and 0.574 mg/kg) in the tub gurnard were higher in comparison with the piper gurnard (0.252, 0.020, and 0.382 mg/kg) caught in the same station in Saros. TTHQs of red mullet and whiting from the same bay were found to be > 1, indicating potential health risks for all nine age categories studied. On the other hand, TTHQs of all species from Saros Bay were determined to be > 1 for the first four age categories, which might trigger health risks for children and adolescents. According to the TR index for Pb, no risk was determined for the fish from both bays. However, TR calculations for inorganic As indicated high cancer risk in most of the age categories for red mullet and whiting from Edremit Bay. To sum up, the results revealed that the fish captured from Edremit Bay posed serious health risks in terms of Hg and As concentrations for all nine age categories. Surveillance and monitoring of toxic metal levels in demersal fish and population-based health risk evaluation are vital in heavily populated bays.

Spatial dynamics and mixing of bluefin tuna in the Atlantic Ocean and Mediterranean Sea revealed using next-generation sequencing.

The Atlantic bluefin tuna is a highly migratory species emblematic of the challenges associated with shared fisheries management. In an effort to resolve the species' stock dynamics, a genomewide search for spatially informative single nucleotide polymorphisms (SNPs) was undertaken, by way of sequencing reduced representation libraries. An allele frequency approach to SNP discovery was used, combining the data of 555 larvae and young-of-the-year (LYOY) into pools representing major geographical areas and mapping against a newly assembled genomic reference. From a set of 184,895 candidate loci, 384 were selected for validation using 167 LYOY. A highly discriminatory genotyping panel of 95 SNPs was ultimately developed by selecting loci with the most pronounced differences between western Atlantic and Mediterranean Sea LYOY. The panel was evaluated by genotyping a different set of LYOY (n = 326), and from these, 77.8% and 82.1% were correctly assigned to western Atlantic and Mediterranean Sea origins, respectively. The panel revealed temporally persistent differentiation among LYOY from the western Atlantic and Mediterranean Sea (FST  = 0.008, p = .034). The composition of six mixed feeding aggregations in the Atlantic Ocean and Mediterranean Sea was characterized using genotypes from medium (n = 184) and large (n = 48) adults, applying population assignment and mixture analyses. The results provide evidence of persistent population structuring across broad geographic areas and extensive mixing in the Atlantic Ocean, particularly in the mid-Atlantic Bight and Gulf of St. Lawrence. The genomic reference and genotyping tools presented here constitute novel resources useful for future research and conservation efforts.

Metazoan gill parasites of the Atlantic bluefin tuna Thunnus thynnus (Linnaeus) (Osteichthyes: Scombridae) from the Mediterranean and their possible use as biological tags.

The gills of 63 specimens of the Atlantic bluefin tuna Thunnus thynnus (Linnaeus) (Osteichthyes: Scombridae) from three localities of the Mediterranean (Sardinian, Tyrrhenian and Levantine Seas) were examined for metazoan parasites. The parasite fauna of T. thynnus from the Sea of Sardinia included 11 species: five didymozoid trematodes, three capsalid and one hexostomid monogeneans, and one caligid and one pseudocycnid copepods. Four didymozoids were found in fish from the Levantine Sea and only one didymozoid was recorded in fish from the Tyrrhenian Sea. Dividing the hosts into four size-groups (small, medium-sized, large and extra large), the pairwise comparison of prevalence and mean abundance of the new and literary data) showed differences according to host size. The differences in the composition of the parasitic faunas and in the prevalence of parasites, observed between the small tunas from the Tyrrhenian Sea and the medium-sized tunas from the Adriatic Sea, Levantine Sea and the North-East (NE) Atlantic Ocean, indicated that these groups form discrete units. The parasite fauna of the large tunas from the Sea of Sardinia is the richest among the bluefin tuna populations of the Mediterranean and the NE Atlantic, due to the presence of species not found elsewhere in bluefin tunas, such as Caligus coryphaenae Steenstrup et Lütken, 1861, Capsala magronum (Ishii, 1936) and C. paucispinosa (Mamaev, 1968). This fact and the prevalence of some parasites of this group (lower than those of medium-sized fish from the NE Atlantic and higher than the small and medium-sized tunas from the Mediterranean) suggest that the large-sized tuna group in the western Mediterranean is formed by Mediterranean resident tunas (poorly infected), and by tunas migrating from the Atlantic Ocean (heavily infected).