Search Results (248)

As a semi-pelagic fish with commercial value, Mediterranean horse mackerel, Trachurus mediterraneus (Steindachner, 1868), is highly important both for the ecosystem, as a link between trophic levels, and for fisheries and local livelihoods. This study investigates the T. mediterraneus stock along the Romanian coast for more than 10 years (2014–2024), reporting the following data on its bio-ecological characteristics and stock status: size, age, sex ratio, and estimated biomass. Horse mackerel at the Romanian coast revealed an initially slower growth rate followed by acceleration in later years, which may reflect local ecological influences such as resource availability, environmental conditions, or selective pressure. The spatial distribution of the species along the Romanian shelf indicates a clear pattern of coastal aggregation, highlighting the need for targeted and precautionary fisheries management measures, aiming to ensure a sustainable stock. Full article

Climate change is disrupting marine ecosystems, necessitating a deeper understanding of environmental and fishing-related impacts on exploited species. This study examines the effects of physical factors (temperature, thermal anomalies, salinity, seabed conditions), biogeochemical elements (pH, oxygen levels, nutrients, primary production), and fishing pressure on the biomass of commercially important species in the Alboran Sea from 1999 to 2022. Data were sourced from the Copernicus observational program, focusing on the geographical sub-area 1 (GSA-1) zone across three depth ranges. Generalized Additive Models were applied for analysis. Rising temperatures and seasonal anomalies have largely negative effects, disrupting species’ physiological balance. Changes in water quality, including improved nutrient and oxygen concentrations, have yielded complex ecological responses. Fishing indices highlight the vulnerability of small pelagic fish to climate change and overfishing, underscoring their economic and ecological significance. These findings stress the urgent need for ecosystem-based management strategies that integrate climate change impacts to ensure sustainable marine resource management. Full article

Alosa immaculata Bennett, 1835, commonly referred to as the Danube shad, is an anadromous pelagic species of the Clupeidae family, and plays a significant economic role for countries bordering the Black Sea. This study investigates the occurrence of both parasites and microplastics in A. immaculata specimens collected from Sfântu Georghe, with the aim of assessing their potential impact on fish health. The overall physiological condition of the fish was evaluated using Fulton’s condition factor (K) to determine whether the presence of parasites or microplastics had any measurable effect. Five parasitic genera were identified, including one ectoparasitic species from the genus Mazocraes, and four endoparasitic species from the genera Pronoprymna, Lecithaster, Hysterotylacium, and Contracaecum. Microplastic analysis showed a dominance of particles measuring 1–5 mm (62.5%), with fibers and foils being the only morphological forms detected. The most common colors were black (45%), transparent (35%), blue (12.5%), and brown (7.5%). The distribution of microplastics was higher in the stomach than intestines. Our findings offer critical insights into the combined effects of parasitic infection and microplastic pollution on this key Black Sea species. The integrated methodology, combining parasite load, microplastic content, and condition factor analysis, marks a novel approach in fish health assessment. Full article

Trachinotus ovatus is a euryhaline, warm-water pelagic fish species with strong adaptability, rapid growth, and a high survival rate, making it one of the most important marine aquaculture species in China. In recent years, extensive experience has been accumulated in the cage farming of T. ovatus, but whether it can adapt to deep-sea environments and grow normally remains a current research focus. This study used RNA-Seq sequencing technology to analyze the gene expression changes in the liver of T. ovatus under three conditions: rest (0 cm/s), medium flow velocity (54 cm/s), and high flow velocity (90 cm/s). Through differential expression analysis, Short Time-series Expression Miner (STEM) analysis and protein–protein interaction (PPI) network analysis, a total of 5107 differentially expressed genes (DEGs), three significantly expressed gene profiles (profile6, profile1, and profile5), and 15 hub genes were identified. The results showed that changes in flow speed significantly impacted key biological processes such as energy metabolism, protein homeostasis, and endoplasmic reticulum (ER) stress response. Under moderate and high flow conditions, glycolysis-related genes were upregulated to meet the energy demands of swimming, while the downregulation of the PPARγ-RXRG complex and its downstream genes in the lipid metabolism pathway suggested a limitation in its fatty acid β-oxidation capacity. At the same time, protein synthesis was enhanced, and the unfolded protein response (UPR) was activated to help cope with ER stress. Furthermore, when the flow speed reached 90 cm/s, the expression of UPR- related genes and the anti-apoptotic factor JNK significantly decreased, suggesting that the stress response was nearing its limit and could potentially trigger cell apoptosis. These findings provide new insights into the molecular adaptation mechanisms of T. ovatus to flow speed stress and offer theoretical support for its rational farming in deep-sea cages, suggesting that the water flow speed in farming should not exceed 90 cm/s. Full article

To investigate the species composition, reproductive dynamics, and hydrological drivers of fish resources in the early stage in the Guiping section of the Xunjiang River, we conducted a two-year survey (2022–2023) downstream of the Datengxia Dam. A total of 22,464 fish eggs and larvae were collected, representing 6 orders, 17 families, and 67 species, with Cyprinidae (58.2%) as the dominant family. Dominant species included Squaliobarbus curriculus, Gobiidae, Hemiculter leucisculus, and Culter, exhibiting significant interannual variation in abundance. The breeding season peaked from May to September, accounting for 94.6% of annual recruitment. Hydrological conditions strongly influenced reproductive output: the multiple flood pulse periods in 2022 (peak discharge: 29,000 m³/s) yielded 34.997 billion eggs and larvae, whereas reduced flows in 2023 (peak discharge: 12,200 m³/s) led to a 75.4% decline (8.620 billion). Redundancy analysis (RDA) revealed that discharge, water temperature, natural hydrological data, and dissolved oxygen were the primary environmental drivers, explaining 46.11% of variability in larval abundance (p < 0.001). Notably, the proportion of important economic fish, “four major Chinese carps”, plummeted from 4.9% (2022) to less than 0.1% (2023), indicating spawning ground function degradation. Our results demonstrate that flood pulses are essential for sustaining fish recruitment, particularly for pelagic spawning riverine fish like the four major Chinese carps. Their proportion plummeted to less than 0.1% in 2023, highlighting the urgent need for eco-hydrological management in the Xunjiang River. Full article

Fish are a valuable source of high-quality protein and essential nutrients, making them an integral component of a healthy diet. However, protein digestibility, influenced by preparation methods, is a critical factor in assessing nutritional quality. This study aimed to evaluate the impact of various thermal processing methods on the protein digestibility of two commonly consumed small pelagic fish species: sardines (Sardina pilchardus) and sprats (Sprattus sprattus). Protein digestibility was assessed using two complementary approaches: total protein digestibility and the Digestible Indispensable Amino Acid Score (DIAAS). Fish samples were subjected to different cooking methods, including boiling, steaming, baking, and frying. All thermal treatments enhanced protein digestibility compared to raw fish. Fried samples exhibited the highest total protein digestibility, with sardines reaching 92.4 ± 4.3% and sprats reaching 89.5 ± 4.4%. DIAAS values corroborated these findings, indicating superior protein quality in fried fish. While frying yielded the highest digestibility scores, steaming and boiling provided a favourable balance between improved protein quality and lower potential health risks, with baking achieving comparable results. Full article

This study analyses for the first time the genetic diversity, connectivity, and evolutionary dynamics of the small red scorpionfish (Scorpaena notata) in the Balearic Islands, using two mitochondrial DNA markers: Cytochrome c oxidase subunit I (COI) and the Control Region (CR). Nucleotide diversity of the COI gene was found to be low compared to other commercial fish species, suggesting that fishing may be impacting the population despite being a by-catch species. In contrast, the CR showed higher genetic variability. Demographic history analyses suggest that S. notata underwent a population expansion during the Pleistocene, possibly driven by sea-level changes. Genetic structure analyses (F_st and AMOVA) indicated genetic homogeneity and high connectivity among the Balearic Islands’ population, likely facilitated by its passive dispersion via pelagic eggs and larvae and the oceanographic conditions of the region. Our results suggest that the entire Balearic Islands could be considered as a unique Management Unit, although its potential relation to other nearby areas, such as the Iberian Peninsula, along with the analysis of additional genetic markers, should be addressed in future studies. Full article

Small pelagic fishes such as Sardinella aurita (Valenciennes, 1847) and Sardinella maderensis (R. T. Lowe, 1838) are key intermediate-level components of the marine food web of the southwestern African coast. Their biomass off Angola has shown significant interannual variability, and information about their reproduction is insufficient in the region for adequate stock management. Thus, we aimed to unveil the reproduction period and reproductive traits of these two Sardinella species and establish a link with the prevailing ocean temperature conditions. Adult fish samples were obtained monthly from artisanal and semi-industrial fleets, and the ichthyoplankton samples were collected with a Hydro-Bios Multinet off southwest Angola by Instituto Nacional de Investigação Pesqueira (Angola). The macroscopic inspection of gonads showed that females of both species were more abundant than males. The gonadosomatic index and maturity stages indicate that S. aurita spawns during the Austral summer (December through March), while S. maderensis has a longer spawning period, from October to April. The spawning peak occurs in February for S. aurita and S. maderensis. The mean monthly condition factor of both species was high before and after spawning seasons. The females of S. aurita reach sexual maturity at a smaller size than males, and 50% of the population reaches sexual maturity at a total length of 31.3 cm. The males of S. maderensis reach sexual maturity at a smaller size than females, and 50% of the population reaches sexual maturity at a total length of 28.4 cm. We also found that both species use the southern coast of Angola as a spawning area during the Austral summer and avoid the area during periods of intense upwelling. Currently, these species are managed as a single unit, and the minimum capture size is set at 22 cm, well below the size at sexual maturity registered in the study area. Therefore, we strongly recommend increasing the minimum capture size to guarantee long-term stock viability. Full article

Age determination through reading annual rings in whole otoliths is a complicated, time-consuming task that can lead to errors in population age structure, negatively affecting marine fish management plans. Recently, Fourier transform near-infrared spectroscopy (FT-NIRS) has been successfully used to evaluate annual age, at least in several long-life fish species. European anchovy (Engraulis encrasicolus) is an important pelagic species for its ecological role and socioeconomic value. In the Mediterranean Sea, anchovy stocks are regularly monitored for assessment purposes, and fish age is calculated by traditional otolith reading. In the present study, anchovies, caught over a decade (2012 to 2023) during on-board surveys in four different areas (i.e., North Tyrrhenian, South Tyrrhenian, North of Sicily, and Strait of Sicily), provided an otolith collection used to acquire absorption spectra by FT-NIRS. These spectra were processed to optimize calibration models, and the best linear models obtained revealed a good predictability for anchovy annual age (coefficient of determination of 0.90, mean squared error 0.3 years, bias < 0.001 years). The calibration model developed for all regions combined proved more robust than the models for each area, demonstrating its efficacy for the entire study area. FT-NIRS analyses proved suitable for predicting age, when applied to E. encrasicolus individuals within the age range of 0 to 3, also when compared to traditional aging methods. Moreover, this methodology improved the standardization of age estimates. Finally, this preliminary study encourages the further application of FT-NIRS also to short-life pelagic species involved in stock assessment plans. Full article

Understanding the ecology of large pelagic fishes is important for species conservation and maintaining ecosystem dynamics. The Atlantic blue marlin (Makaira nigricans) is usually targeted in recreational fisheries and occasionally captured as bycatch in pelagic longline fisheries, yet it is considered an overexploited stock in the Atlantic. In this study, pop-up archival satellite tags were deployed on twenty-one blue marlins in the Southwest Atlantic Ocean between February 2006 and August 2021. Results show that blue marlin spent an average of 57% of their time in shallow waters (<10 m) and mostly at temperatures between 26 °C and 28 °C during both day and night. Minimum linear distances observed ranged from 124 to 1995 km, with tracking periods lasting 5 to 215 days. Overall, tagged blue marlins remained around the tagging region during the tracking period, except for six individuals that exhibited more directional movements offshore. The results provided in this study are relevant for better understanding the habitat use of blue marlins in the Southwest Atlantic Ocean and to support analysis for stock assessment purposes, which are often affected by uncertainties and large misreporting rates in the region. Full article

Chub mackerel (Scomber japonicus) is a typical small pelagic fish in the high seas of the Northwest Pacific Ocean (NPO), with great ecological and economic values. It is crucial to understand the spatio-temporal distribution and the population dynamics of chub mackerel for commercial fishing and fishery management. In this study, we analyzed the population dynamics and stock status of chub mackerel based on commercial fishing data. Results showed that from 2016 to 2021, high catches of chub mackerel were concentrated along the outer edge of Japan or Russia’s exclusive economic zone line, and the gravity center of the fishing grounds moved to the northwest gradually, with a decrease in the average value of catch per unit effort (CPUE) year by year. The fishing pressure may not be the major reason for the decrease in chub mackerel as the resource biomass was at a high level. The body length structure was reasonable, and large individuals were still present. The study highlights the fact that the population status of chub mackerel was healthy in 2016–2021 according to our results. However, it has to be emphasized that resource exploitation and fishery management also need to take into account the influence of climatic conditions. Full article

Cold-water lakes in high-latitude regions are experiencing rapid changes in community structure and functioning associated with local and global stressors (e.g., climate change, hydropower and invasive species). However, the long-term ecological responses of cold-adapted top predators are relatively poorly monitored despite their high importance for structuring ecological communities and for the provisioning of ecosystem services. We studied long-term changes (2010–2021) in the population structure and trophic niche of two cold-adapted coregonid fishes in oligotrophic Lake Osensjøen, southeastern Norway. Our gillnet surveys indicated that the whitefish (Coregonus lavaretus) population declines simultaneously with the increasing population density of roach (Rutilus rutilus), whereas vendace (Coregonus albula) showed more stable densities. Both whitefish and vendace became increasingly dominated by small-sized individuals following the increase in coexisting roach and perch (Perca fluviatilis) populations. Our stomach content and stable isotope data indicated a marked overlap in the trophic niches of whitefish and roach, with both species showing high among-individual variation in δ¹³C and δ¹⁵N values as compared to the more specialized zooplanktivorous vendace. Our study provides further evidence that the ongoing environmental changes in high-latitude lakes may induce rapid changes in community structures and lead to the population declines of cold-adapted fishes, likely associated with strong resource competition with warm-adapted cyprinid and percid fishes. Such shifts in fish community structure may, in turn, affect the benthic and pelagic food-web compartments and reduce valuable ecosystem services such as local fisheries targeting salmonids. Full article

The mercury (Hg) present in ocean fish has caused concern regarding the effects of maternal consumption on child outcomes but it is now recognized that mothers that eat more ocean fish during pregnancy have children with higher social, scholastic, and IQ scores. These findings coincide with the current understanding of the mechanism of Hg toxicity which indicates ocean fish consumption will prevent rather than cause harm. High-Hg exposures sequester selenium (Se) and inhibit Se-dependent enzymes that prevent and reverse oxidative damage in the brain and support fetal brain development. However, aside from certain types of shark and other apex marine predators, seafood contains more Se than Hg and thus counteracts instead of contributing to Hg toxicity. This study evaluates the Hg and Se present in bigeye tuna, yellowfin tuna, albacore tuna, skipjack, swordfish, striped marlin, blue marlin, spearfish, mahimahi, wahoo, monchong, escolar, mako shark, and thresher shark to establish their health benefit values (HBVs). Positive HBVs (0.3–19.6), indicating a molar excess of Se over Hg, were found in 14 of the 15 species studied. Only mako shark uniformly contained Hg in excess of Se to produce a negative HBV (−16.4), indicating its consumption should be minimized during pregnancy. Full article

Environmental DNA (eDNA) metabarcoding was utilized to compare the fish species composition, diversity, and their relationships with environmental factors in four medium-sized drinking water reservoirs (Tongjiqiao, Andi, Shafan, and Jinlan) within the Qiantang River Basin during both wet and dry seasons. A total of 44 fish species belonging to 6 orders, 15 families, and 40 genera were detected, with Cyprinidae being identified as the dominant family (68.2%). Silver carp (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis) were identified as the most abundant species, representing 81.94% and 99.98% of the relative eDNA abundance, respectively. The fish communities were characterized by river-resident species (59.1%), pelagic species (43.2%), and omnivorous (43.2%) and carnivorous (43.2%) feeding habits. Significant influences of seasonal and reservoir-specific variations on physicochemical parameters, species composition, and ecological traits were observed. However, no significant differences in community diversity (Chao1, Pielou_e, Shannon, and Simpson indices) or distribution patterns were detected between wet and dry seasons. In contrast, Jinlan Reservoir was found to exhibit distinct diversity and distribution patterns compared to the other three reservoirs, which was consistent with the relative eDNA abundance of H. molitrix and H. nobilis. Through a Spearman correlation analysis, the relative abundance of H. molitrix was revealed to be negatively correlated with community diversity, while H. nobilis was shown to have positive correlations (except with Chao1). This suggests that the excessive stocking of H. molitrix may lead to reduced diversity, whereas moderate stocking of H. nobilis could promote diversity restoration. Among physicochemical factors, Chao1 richness was found to be negatively correlated with conductivity, pH, phosphate–phosphorus (PO₄-P), and the total nitrogen to total phosphorus ratio (TN/TP), while Shannon and Simpson diversity indices were negatively correlated with nitrate nitrogen (NO₃-N) concentrations. A redundancy analysis (RDA) identified NO₃-N and permanganate index (COD_Mn) as the primary physicochemical drivers of fish community structure, indicating that while physicochemical differences were found to influence species composition and diversity, their effects were considered relatively limited. These findings suggest that the overwhelming dominance of H. molitrix and H. nobilis in the reservoirs may reduce the influence of seasonal variations and cross-reservoir physicochemical disparities on fish community dynamics. Full article

The large pelagic species play an important role in transferring energy in vast distant marine ecoregions. Results obtained report on extraordinary findings of important commercial species in southeast–south Brazilian waters, including the Southern bluefin tuna Thunnus maccoyii and the Pacific bluefin tuna Thunnus orientalis, an endemic species from the Pacific Ocean. These specimens were identified within the genomic description of 10 individuals randomly selected from the catch to evaluate the catch composition of pelagic longline fisheries off Brazilian waters. Most of the records were from T. maccoyii (6), followed by the Bigeye tuna T. obesus (2), Yellowfin tuna T. albacares (1), and T. orientalis (1). Yellowfin and Bigeye tuna are expected to be captured in the vicinity of the longline fishing areas. However, the unlikely presence of the cold-water T. maccoyii and the warm-water T. orientalis suggests a long migration from common species ranges that could be influenced by climate change. These results imply a readjustment of spatial management structures for these species. Full article