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Selenoneine is a selenium-containing imidazole compound in the blood and tissues of tuna and other marine fish that has strong free-radical scavenging activity. This compound may have antioxidant functions, i.e., preventing metmyoglobin formation in fish muscle, which affects meat quality. This study examined the relationship between meat color and total selenium concentration in the muscle of two Scomber species, spotted mackerel (Scomber australasicus) and Pacific mackerel (S. japonicus), to assess the role of selenium as an antioxidant preventing meat discoloration. The color of chilled and frozen-thawed muscle was compared between spotted mackerel and Pacific mackerel. The a* values, indicating the red-green component of color, of the white and red muscle of spotted mackerel were higher than those of Pacific mackerel (p < 0.05). We also analyzed the blood selenium concentration of Pacific mackerel according to the L* value and protein concentration in the blood during spawning migration in June. The blood selenium concentration was negatively correlated with the L* value (r =  − 0.46) and blood protein concentration (r =  − 0.56). The blood selenium concentration in summer was related to the brightness of the muscle surface and blood protein concentration, suggesting that it is responsible for deterioration of meat quality.These findings suggest that antioxidant properties of selenium prevent the mackerel muscle discoloration that can occur during chilled and frozen storage.

A new species of Prodistomum (Digenea, Lepocreadiidae), Prodistomum chumphonense sp. nov., is described from the intestine of Rastrelliger kanagurta and Rastrelliger brachysoma (Scombridae) collected in the Gulf of Thailand. The new species is characterized by vitelline follicles confined to the hindbody but extending anteriorly to the level of the anterior to posterior margin of the ventral sucker; a ventral sucker consistently larger than the oral sucker; an esophageal region approximately equal in length to the prepharynx; an entire, oval ovary; and a tubular excretory vesicle terminating below the level of the intestinal bifurcation. The new species differs from most congeners, mainly those with vitelline follicles extending into the forebody, by the restriction of the vitellarium to the hindbody. Although morphometrically similar to some specimens in the literature previously identified as P. orientale, previous molecular phylogenetic analyses based on 18S, ITS2, and 28S rDNA sequences demonstrate that P. chumphonense sp. nov. represents a distinct taxon. The present study underscores the importance of integrating detailed morphometric with molecular data for accurate species delimitation in trematodes of the genus Prodistomum.

Overfishing remains a global concern, however effective management from well valuation of fisheries may efficiently reduce the impact of fishing. Therefore, it is important to evaluate the biomass of Indian Mackerel fishery in order to maintain the stock. Catch-based Monte Carlo maximum sustainable yield (CMSY) method and Length-based Bayesian Biomass (LBB) methods are frequently used to evaluate fish stock. Eighteen years effort-catch and length frequency data from commercial fishing were utilize to estimate the current biomass. The calculated biological reference points from Bayesian state-space Schaefer production model (BSM) at r = 0.618, k = 68,700, maximum sustainable yield (MSY) = 10,600. However, CMSY at r = 0.662, k = 6800, MSY = 11,200. Biomass in 2021 at maximum sustainable yield 2021 (B2021/BMSY) = 0.436 (< 1) and fishing rate F2021/FMSY = 1.94 (> 1) values explain the Indian Mackerel fishery is at exploited state. However, results using LBB model defines as B/BMSY = 0.65 (< 1.0) and fishing rate F/FMSY = 3.33 (> 1.0) and mean length/optimum length (Lmean/ Lopt) obtained at 1.3 and L95th/ Linf at 0.95. Based on suggested prior biomass range (B/BMSY =0.5–0.8) for stock assessment also indicates that the Indian Mackerel fishery is in unsustainable state from the study area. Monitoring of illicit fishing practices in the area is recommended. Measures need to be implemented for the protection of these valuable resources.

Environmental DNA (eDNA) has become a popular non‐invasive method to study the presence of organisms in the environment. To study the ecological behavior and migration routes of small pelagic fishes that are difficult to trace with traditional capturing methods, we developed multiplex real‐time PCR assays to measure the eDNA of chub mackerel, blue mackerel, Japanese jack mackerel, Japanese anchovy, Japanese sardine, and Pacific saury. To test the validity, eDNA samples collected from the water near fisherman set nets in Northeast Japan between 2018 and 2019 were analyzed. Warm‐climate species including blue mackerel, jack mackerel, and anchovy were prominent in autumn, while cold‐climate species such as chub mackerel and sardine were richly present in winter. Pacific saury is an off‐coast species and was not detected in the coastal set net area. The eDNA data were partially correlated to the fishery catch records, suggesting that the eDNA quantities are relevant to the biomass of the fish schools, and our PCR assays can quantify the biological traces left by the small pelagic fish schools. Different patterns of eDNA occurrence were observed between the chub and blue mackerels, indicating that the specificity of the multiplex assay is applicable to field samples to measure the presence of the two closely related species separately. The methods are useful to evaluate the eDNA samples collected from the open water in the North Pacific to elucidate the life cycles and monitor the sustainability of the small pelagic fishes, which not only are important food sources, but also carry a role in the Japanese food culture. Multiplex qPCR assays for 6 types of small pelagic fishes were developed to measure environmental DNA from open water to infer the occurrence of fish schools. The method sensitivity and specificity were tested using field samples obtained from fisherman's set nets. The developed method paves a way to trace the ontogenetic migration of small pelagic fishes in the North Pacific.

The Mediterranean is one of the most overfished seas of the world where mesopredators are severely threatened. The trophic strategies of four pelagic species that inhabit the Adriatic Sea (Scomber spp. and Trachurus spp.) were investigated through an integrated approach of stomach contents and stable isotopes analyses. Our study demonstrated that Scomber colias feeds mainly on strictly pelagic prey, with fish larvae as a secondary prey in the Southern Adriatic Sea, while S. scombrus feeds on prey belonging to higher trophic levels. Smaller specimens of Trachurus mediterraneus have a diet mainly based on pelagic prey, while larger fishes rely on prey such as benthic decapods, showing an ontogenetic shift in the diet of the species. Trachurus trachurus shows a preference for offshore and deeper areas and a diet such as that of its congeneric, but no clear ontogenetic shift was observed. This spatial segregation allows the co-existence of these two species of Trachurus. Scomber colias mainly inhabits southern areas and S. scombrus shows a preference for the northern sectors. This latitudinal gradient avoids the overlap of their trophic niches. Bayesian mixing models confirmed that the trophic niches of these species only partially overlap in the middle of the trophic web.

Population dynamics of small pelagic fishes (SPF) and their management in Japan were reviewed for Japanese sardine Sardinops melanostictus, Japanese anchovy Engraulis japonicus, chub mackerel Scomber japonicus, and Pacific saury Cololabis saira. The catch and biomass of SPF generally showed decadal-scale variability with prominent species replacements since the 1900s. The causes of species replacements were generally associated with climatic/oceanic variability, particularly “regime shifts,” of which the 1988/89 regime shift was the most influential since the 1970s. Variability in the early survival rate is a key factor for population fluctuations, and the proposed hypothetical mechanisms of recruitment variability are summarized herein. Although overfishing during the 1990s and early 2000s prevented the recovery of Pacific stocks of sardine and chub mackerel, they have been recovering since the mid-2000s owing to strong year classes and reduced exploitation rates. The fundamental cause of overfishing was derived from a mismatch between investments in larger purse seine fleets during the 1980s and poor ocean productivity since the 1988/89 regime shift, when dominant SPF began to shift from sardine to anchovy. Recommendations for fisheries management of SPF around the Japanese Archipelago are proposed, considering climate change and naturally and drastically changing SPF populations.

Microplastics (MP) have been confirmed as emerging pollutants in the marine environment due to their ubiquity, bioavailability, persistence and potential toxicity. This study contributes with valuable data regarding the abundance and characteristics of the MP found in five species collected from Portugal. The mussel Mytilus galloprovincialis ( n = 140) was collected from the Tagus estuary and Porto Covo coastal area, the peppery furrow shell Scrobicularia plana ( n = 140) and the polychaete Marphysa sanguinea ( n = 30) both from the Sado estuary, and Trachurus trachurus ( n = 82) and Scomber colias ( n = 82) fished off Figueira da Foz and Sesimbra. Soft tissues of all individuals were digested using a KOH (10%) solution, which allowed the extraction of MP. All studied species presented MP. In a total of 502 MP observed from all samples, 80% were fibers and 20% were fragments, with a size range of 73 μm–4,680 μm and blue was the most common color recorded (46%). The frequency of occurrence of MP was higher in T. trachurus (70%) and lowest in M. sanguinea (17%). MP abundance ranged from 0.30 ± 0.63 MP. ind −1 in S. plana , to 2.46 ± 4.12 MP. ind −1 in S. colias . No significant correlation was found between the individual biometric parameters and total MP, fibers and fragments ingested by each species. The FTIR analysis revealed that polyester and polyethylene were the most common polymers present. These results can be used as a reference for future studies regarding the use of indicator species for monitoring MP pollution in the coast of Portugal.

The gill tissue is the main site of metabolic enzymes or compensation, with the kidney tissue playing a supporting role. At the gill tissue, carbonic anhydrase enzymes (CAs) catalyze the hydration of CO 2 to HCO 3 − and H + for production to the H 2 O. In this work, the CA enzyme was purified from horse mackerel ( Trachurus trachurus ) gill with a specific activity of 21,381.42 EU/mg, purification fold of 150.61, total activity of 2347.68 EU/mL, and a yield of 16.13% using sepharose 4B-L-tyrosine-sulfanilamide affinity gel chromatography. For recording the enzyme purity, gel electrophoresis was performed, and single band was seen. The molecular weight of this enzyme was found approximately 35 kDa. Also, the inhibitory effects of different pesticides such as thiram, clofentezine, propineb, deltamethrin, azoxystrobin, and thiophanate and heavy metal ions such as Fe 2+ , Cu 2+ , Co 2+ , Pb 2+ Hg 2+ , and As 3+ on horse mackerel gill tissue CA enzyme activities were investigated. Our results indicated that these pesticides and metal ions showed inhibitory effects at low nanomolar and millimolar concentrations for fish gill CA enzymes, respectively.

Microplastics (MPs) ingestion by fish signifies a worldwide threat to human health but limited research has examined their existence within the consumable portions (muscle) of fish. Thus, this study was undertaken to unveil the prevalence, characterization, and contamination extent of MPs across various body tissues, including the muscle of the king mackerel (S. guttatus) from the lower Meghna estuary in Bangladesh—a pioneering investigation in this region. In our analysis, we identified a total of 487 MPs, with an average abundance of 48.7 ± 20.3 MPs/individual. These MPs were distributed across different tissues, with respective concentrations of 0.84 ± 0.45 items/g in the digestive tract, 2.56 ± 0.73 items/g in the gills, and 0.3 ± 1.72 items/g in the muscle tissue. The observed variations among these tissue types were statistically significant (p < 0.05). Moreover, a significant positive correlation indicated that fish with higher weight had higher MPs in their gills and DT (digestive tract). The majority were <0.5 mm in size (97.74%) and exhibited a fiber-like shape (97.74%), with a notable prevalence of transparent (25.87%) and a pink coloration (27.92%). Remarkably, the majority of MPs were discovered within the size range of <0.5–1 mm (100%), particularly in the muscle tissue, signifying a substantial transfer of MPs into the human diet. Besides, we discovered only three polymer types of microplastics which could be attributed to the extensive use of food packaging, plastic containers, wrapping plastics, residential garbage, and plastic pipes that end up in the aquatic environment via river discharges. The contamination factor (CF) values of fish muscle (5.75) and the digestive tract (5.50) indicated that these fish organs were considerably contaminated (3 < CF < 6) with MPs. The pollution index of MPs (PLI > 1) indicated a high contamination level for MPs pollution of S. guttatus in the lower Meghna River estuary.

Indian mackerel has a lot of demand in the community because it has high economic value and high nutritional value. The study aims to determine the types of food consumed by Indian mackerel and determine the food habits of fish. Research on the food habits of Indian Mackerel ( Rastrelliger kanagurta ) at the TPI Pantai Labu, Deli Serdang Regency, which was carried out in September – November 2022. The number of Indian Mackerel samples in this study was 264 individuals. The total length of the observed fish is between 120 – 335 mm. The relative gut length of mackerel is 1.19 so the fish is classified as an omnivorous fish, index of stomach content ranges from 1.012 to 1.018. The main food for mackerel is phytoplankton, complementary food is zooplankton and gastropods, and additional food is worms, squids, anchovies, and shrimp.