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Concept: Atlantic mackerel

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Microplastics are highly bioavailable to marine organisms, either through direct ingestion, or indirectly by trophic transfer from contaminated prey. The latter has been observed for low-trophic level organisms in laboratory conditions, yet empirical evidence in high trophic-level taxa is lacking. In natura studies face difficulties when dealing with contamination and differentiating between directly and indirectly ingested microplastics. The ethical constraints of subjecting large organisms, such as marine mammals, to laboratory investigations hinder the resolution of these limitations. Here, these issues were resolved by analysing sub-samples of scat from captive grey seals (Halichoerus grypus) and whole digestive tracts of the wild-caught Atlantic mackerel (Scomber scombrus) they are fed upon. An enzymatic digestion protocol was employed to remove excess organic material and facilitate visual detection of synthetic particles without damaging them. Polymer type was confirmed using Fourier-Transform Infrared (FTIR) spectroscopy. Extensive contamination control measures were implemented throughout. Approximately half of scat subsamples (48%; n = 15) and a third of fish (32%; n = 10) contained 1-4 microplastics. Particles were mainly black, clear, red and blue in colour. Mean lengths were 1.5 mm and 2 mm in scats and fish respectively. Ethylene propylene was the most frequently detected polymer type in both. Our findings suggest trophic transfer represents an indirect, yet potentially major, pathway of microplastic ingestion for any species whose feeding ecology involves the consumption of whole prey, including humans.

Concepts: Digestive system, Digestion, Apex predator, Pinniped, Gray Seal, Scombridae, Atlantic mackerel, Mackerel

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Didymozoids found in the muscles of marine fish are almost always damaged because they are usually found after being sliced. Therefore, identifying muscle-parasitizing didymozoids is difficult because of the difficulty in collecting non-damaged worms and observing their organs as key points for morphological identification. Moreover, muscle-parasitizing didymozoids are not easily found because they parasitize at the trunk muscles. Therefore, muscle-parasitizing didymozoid classification has not progressed because there are few opportunities to detect them. Our recent report was the first to describe the usefulness of sequencing analysis for discrimination among muscle-parasitizing didymozoids. Recently, we found a didymozoid in the trunk muscle of a chub mackerel Scomber japonicus. The present study genetically compares the present isolate with other muscle-parasitizing didymozoids. The present isolate differs markedly from the previously unidentified didymozoid from an Atlantic mackerel S. scombrus by phylogenetic analysis of 18S rDNA. It also differs from other muscle-parasitizing didymozoids from other host species based on phylogenetic analyses of 18S, 28S rDNAs, and coxI loci. These results suggest that sequencing analysis is useful for the discrimination of muscle-parasitizing didymozoids. Combining the present data with earlier data for sequencing analysis, muscle-parasitizing didymozoids from seven marine fish species were classified as seven species. We proposed appellations for six distinct muscle-parasitizing didymozoids for future analysis: sweetlips fish type from Diagramma pictum and Plectorhinchus cinctus, red sea bream type from Pagrus major, flying fish type from Cypselurus heterurus, Atlantic mackerel type from Scomber scombrus, chub mackerel type from S. japonicus, and purple rockcod type from Epinephelus cyanopodus.

Concepts: Biology, Sparidae, Scombridae, Atlantic mackerel, Mackerel, Scomber, Atlantic Spanish mackerel, Chub mackerel

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The present research focused on the quality of canned fish. Its primary objective was the quality enhancement of canned Atlantic mackerel (Scomber scombrus) by including an aqueous Bifurcaria bifurcata extract in the packing medium. Various alga extract concentrations were tested and compared to a control without alga extract. After a 3-month canned storage, the cans were opened, and quality changes in fish white muscle were analyzed.

Concepts: Present, Muscle, Scombridae, Atlantic mackerel, Mackerel, Scomber, Atlantic Spanish mackerel

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The selectivity of fishing gears with respect to fish species and size is important, both for fisheries management and fishing operations. Purse seining is an efficient, environmentally friendly fish capture methodology generally targeting single species aggregations, but once a fish school has been selected and surrounded by the seine, there is no selections for individual size, species or catch quantity. A common practice for evaluating the catch is to haul the seine to a point where physical samples or inspections of catch composition can be made. The release process is called slipping and may lead to mortality in the released fish. The objective of this study was to simulate a crowding situation and investigate how the behaviour was affected in response to increased fish density, decreased oxygen levels, or a combination of the two, and to see if there is a behavioural measure that can be used to set safe crowding limits. The experiment was conducted on Mackerel (Scomber scombrus) held in net pens. The volume of the net pen was reduced to increase fish density, and a tarpaulin bag was wrapped around the pen to reduce the oxygen levels. Oxygen, fish density and space occupancy was monitored during the experiment, and the behavioural reactions was assessed using an imaging sonar. The main result was that the schooling function, i.e. the response to a predator model, was significantly reduced during crowding but not in response to hypoxia. There were some indications of a slow recovery of the function post-treatment. We conclude that crowding causes behavioural responses that occur before densities that induce fish mortality. Consequently, there is a behavioural response that could be used as a proxy for setting safe crowding limits.

Concepts: Density, Fish, Fishing, Overfishing, Scombridae, Atlantic mackerel, Mackerel, Fishing net

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The objective of the present study was to evaluate the impact of rosemary and basil essential oils (EOs) on the qualityof Atlantic mackerel fillets stored at 2°C up to 15 days. Atlantic mackerel (<em>Scomber scombrus</em>) fillets were periodically evaluated to assess their textural, color, physicochemical, and spectral characteristics. The results indicated that rosemary and basil treatments were effective for inhibiting the formation of total volatile basic nitrogen (TVB-N) and lipid oxidation products during storage. Based on TVB-N values, the shelf life of Atlantic mackerel fillets treated with rosemary and basil EOs was extended by 2 and 5 days, respectively, compared to the control group. Similar results were obtained with thiobarbituric acid-reactive substance analysis, which demonstrated an extended shelf life of Atlantic mackerel immersed with rosemary and basil EOs of 2 and 3 days, respectively, compared to the control group. The factorial discriminant analysis applied on the concatenated first five principal components corresponding to the physicochemical, textural, color, and fluorescence measurements allowed clear discrimination of the three groups, because a correct classification rate of 93.3% was obtained. Therefore, treatment with basil and rosemary EOs, as natural biopreservative compounds, could present ahigh-potential application in the seafood industry.

Concepts: Essential oil, Shelf life, Scombridae, Atlantic mackerel, Mackerel, Scomber

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An analytical method based on pressurised liquid extraction (PLE) followed by liquid chromatography-high resolution mass spectrometry (Orbitrap) was developed for the simultaneous determination of ten high-intensity sweeteners in fish samples. As the method was developed, the different PLE parameters were optimised and different clean-up strategies were evaluated, of which in-cell clean-up using alumina and on-cell clean-up with hexane were the most effective. PLE recoveries were between 43% and 94%. The method quantification limits were between 12.5ngg(-1) dry weight (d.w.) and 250ngg(-1) (d.w.) and the method detection limits between 2.5ngg(-1) (d.w.) and 125ngg(-1) (d.w.). Intra-day precision and inter-day precision were below 16% and 25%, respectively. Fish samples from different species were analysed and, saccharin was found below its method quantification limit in the species Scomber scombrus (Atlantic mackerel).

Concepts: Mass spectrometry, Calculus, Sweeteners, Scombridae, Atlantic mackerel, Mackerel, Scomber, Atlantic Spanish mackerel

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Restriction-site associated DNA sequencing (RAD-seq) and related methods are revolutionizing the field of population genomics in non-model organisms as they allow generating an unprecedented number of single nucleotide polymorphisms (SNPs) even when no genomic information is available. Yet, RAD-seq data analyses rely on assumptions on nature and number of nucleotide variants present in a single locus, the choice of which may lead to an under- or overestimated number of SNPs and/or to incorrectly called genotypes. Using the Atlantic mackerel (Scomber scombrus L.) and a close relative, the Atlantic chub mackerel (Scomber colias), as case study, here we explore the sensitivity of population structure inferences to two crucial aspects in RAD-seq data analysis: the maximum number of mismatches allowed to merge reads into a locus and the relatedness of the individuals used for genotype calling and SNP selection. Our study resolves the population structure of the Atlantic mackerel, but, most importantly, provides insights into the effects of alternative RAD-seq data analysis strategies on population structure inferences that are directly applicable to other species. This article is protected by copyright. All rights reserved.

Concepts: DNA, Gene, Genetics, Bioinformatics, Population genetics, Scombridae, Atlantic mackerel, Scomber

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The Norwegian spring-spawning (NSS) herring (Clupea harengus), blue whiting (Micromesistius poutassou) and Northeast Atlantic (NEA) mackerel (Scomber scombrus) are extremely abundant pelagic planktivores that feed in the Norwegian Sea (NS) during spring and summer. This study investigated the feeding ecology and diet composition of these commercially important fish stocks on the basis of biological data, including an extensive set of stomach samples in combination with hydrographical data, zooplankton samples and acoustic abundance data from 12 stock monitoring surveys carried out in 2005-2010. Mackerel were absent during the spring, but had generally high feeding overlap with herring in the summer, with a diet mainly based on calanoid copepods, especially Calanus finmarchicus, as well as a similar diet width. Stomach fullness in herring diminished from spring to summer and feeding incidence was lower than that of mackerel in summer. However, stomach fullness did not differ between the two species, indicating that herring maintain an equally efficient pattern of feeding as mackerel in summer, but on a diet that is less dominated by copepods and is more reliant on larger prey. Blue whiting tended to have a low dietary overlap with mackerel and herring, with larger prey such as euphausiids and amphipods dominating, and stomach fullness and feeding incidence increasing with length. For all the species, feeding incidence increased with decreasing temperature, and for mackerel so did stomach fullness, indicating that feeding activity is highest in areas associated with colder water masses. Significant annual effects on diet composition and feeding-related variables suggested that the three species are able to adapt to different food and environmental conditions. These annual effects are likely to have an important impact on the predation pressure on different plankton groups and the carrying capacity of individual systems, and emphasise the importance of regular monitoring of pelagic fish diets.

Concepts: Fish, Ecology, Zooplankton, Plankton, Scombridae, Calanoida, Atlantic mackerel, Mackerel

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Proteins from fish by-product sources are valuable source of bioactive peptides and show promise as functional foods ingredients. The objective of the present study was to isolate and characterize antibacterial peptides from protamex hydrolysates of Atlantic mackerel (Scomber scombrus) by-products. Four sequences SIFIQRFTT (P4), RKSGDPLGR (P8.1), AKPGDGAGSGPR (P8.2) and GLPGPLGPAGPK (P11) were identified in peptide fractions separated using RP-HPLC. At 200 μg mL(-1), while peptides P8.1, P8.2 and P11 exhibited partial inhibition, P4 totally inhibited tested Gram-positive (Listeria innocua) and Gram-negative (Escherichia coli) bacterial strains. These results suggest that the protein hydrolysate derived from mackerel by-products could be used as an antimicrobial ingredient in both functional food and nutraceutical applications.

Concepts: Protein, Bacteria, Amino acid, Nutrition, Microbiology, Escherichia coli, Scombridae, Atlantic mackerel

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Mackerel is marketed at prices according to the species type, Scomber japonicus and Scomber scombrus. Distinguishing these two species with the naked eye is difficult, and their differentiation becomes more difficult after they are processed by cooking, thereby leading to counterfeiting issues. Thus, in this study, we developed a method to differentiate S. japonicus from S. scombrus by detecting polymorphisms in mitochondrial 16 s rRNA gene by using fluorescence melting curve analysis and locked nucleic acid probes. Our method could distinguish S. japonicus from S. scombrus in a single experiment by using a single probe. The probes developed matched exactly with S. japonicus and had a melting temperature of 64 °C. However, the probes were mismatched with S. scombrus, resulting in a lower melting temperature of 46 °C. The high specificity of the locked nucleic acid probes resulted in this large difference in the melting temperatures.

Concepts: DNA, Gene expression, RNA, Solid, Liquid, Scombridae, Atlantic mackerel, Scomber