Search Results (44)

The reproductive contribution of river-resident (freshwater) Japanese eels (Anguilla japonica) remains poorly understood, particularly following recent paradigm shifts that emphasise the predominance of ocean-resident “sea eels.” To elucidate the riverine life history and maturation strategies of freshwater residents, we investigated the age structure, morphological traits, and gonadal development of 100 river-resident Japanese eels captured over a three-year period (2007–2009: n = 33, 40, and 27, respectively) in the middle reaches (25–50 km upstream) of the Oi River, Shizuoka Prefecture, Japan. Age determination using sagittal otoliths revealed a broad age distribution from 4 to 15 years. Among the female population (n = 85), highly significant positive correlations were observed between age and growth parameters (Total Length, R² = 0.771; Body Weight, R² = 0.709; p < 0.001). Highly mature silver eels with markedly elevated gonadosomatic indices (GSI) were captured at the uppermost sampling site, immediately downstream of an impassable dam barrier. This spatial concentration of mature females suggests an energetic and temporal life-history strategy in which river-resident eels initiate precocious maturation in the upper reaches to compensate for the prolonged downstream migration to the river mouth. Notably, the calculated female growth rate of approximately 3.6 cm/year was significantly slower than that reported for coastal and estuarine conspecifics in Japan, indicating a distinct slow-growth history unique to river-resident cohorts. Although historical baselines exhibit significant annual variation (ANOVA, p < 0.05), they provide an invaluable benchmark for river-resident cohorts prior to the severe depletion of wild stocks. Our findings underscore that large freshwater-resident females may serve as vital somatic and reproductive reserves, and provide key recommendations for rigorous habitat conservation within river systems to sustain the species. Full article

This study evaluated how graded dietary nucleotide supplementation (0, 0.25, 0.5, 0.75, 1.0, and 2.0 g/kg) affects growth performance, antioxidant capacity, intestinal morphology, and gut microbiota in swamp eel (Monopterus albus) (initial body weight 10.07 ± 0.92 g). Three hundred sixty fish were randomly assigned to six diets, each in triplicate, for eight weeks. Compared with the control, nucleotide addition significantly increased final body weight, weight gain rate, and specific growth rate, and decreased feed conversion ratio (p < 0.05), with optimal results at 0.75 g/kg (HS3). Survival was 100% in all groups. Supplemented fish showed lower serum and intestinal malondialdehyde levels and higher superoxide dismutase and catalase activities (p < 0.05). Serum total protein, albumin, and triglycerides increased, whereas alanine aminotransferase, aspartate aminotransferase, and γ-glutamyl transpeptidase decreased (p < 0.05), pointing to improved hepatic and lipid metabolism. Intestinal trypsin, lipase, and amylase activities also rose markedly (p < 0.05), peaking in HS3. Histological examination revealed greater mucosal thickness and villus height (p < 0.05); in HS3, these values reached approximately 0.95 mm and 0.87 mm, respectively. Metagenomic analysis showed that 0.75–1.0 g/kg nucleotides increased alpha diversity and restructured the microbial community, enriching Bacteroidetes- and Prevotella-related taxa while reducing Proteobacteria, including Acinetobacter baumannii and Escherichia coli. LEfSe identified dose-specific discriminant taxa, and refined KEGG Level 3 pathway analysis predicted enhanced butyrate and propanoate biosynthesis, starch utilization, and purine/pyrimidine interconversion at moderate doses. Genus-level abundances of Prevotella and Bacteroides correlated inversely with serum oxidative and hepatic stress markers. Quadratic regression estimated the optimal dietary nucleotide level at 764 mg/kg (0.76 g/kg), consistent with the best-performing 0.75 g/kg group. Collectively, 0.75–0.76 g/kg dietary nucleotides optimize growth and intestinal health in M. albus through coordinated improvements in antioxidant status, digestive function, mucosal architecture, and beneficial gut microbiota remodeling. Full article

Focused-ion-beam scanning electron microscopy (FIB-SEM) provides site-specific access to buried interfaces, particle interiors, porous electrode architectures, and localized degradation regions in energy materials. This capability is particularly valuable for rechargeable batteries, solid-state ion conductors, alkali-metal electrodes, and reactive solid–liquid interfaces, where the structures governing transport and failure are rarely exposed at a free surface. However, the preparation and imaging steps that reveal these regions may also alter them. Ion milling, environmental transfer, vacuum exposure, scanning electron microscopy (SEM), cryogenic handling, transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDS), electron energy-loss spectroscopy (EELS), and atom probe tomography (APT) can each modify local morphology, chemistry, or phase state. These effects are especially important when the intended evidence involves light elements, metastable phases, nanoscale coatings, reactive interphases, volatile species, or ion-conducting materials. This perspective develops a claim-specific framework for evaluating such results. Preparation- and imaging-induced changes are related to the material feature being interpreted and to the minimum control needed to distinguish the two origins. For porous electrodes, the relevant outputs include pore volume, connectivity, tortuosity, crack geometry, phase fraction, and active surface area. For reactive interfaces and solid electrolytes, the critical questions concern alkali-metal redistribution, surface amorphization, light-element contrast, implanted-species chemistry, and beam-induced phase formation. The discussion further compares conventional Ga-FIB, cryogenic FIB, Xe plasma FIB, low-energy Ar+ polishing, broad-ion-beam preparation, ultramicrotomy, and repeated particle-oriented FIB workflows. Reliable interpretation requires the preparation route, transfer conditions, imaging dose, analytical acquisition, and claim-specific controls to be reported together with the final microscopy result. Full article

The zig-zag eel (Mastacembelus armatus) exhibits sexual dimorphism in growth patterns. Identifying the genes involved in sex differentiation is a crucial step toward achieving single-sex breeding and serves as a vital foundation for elucidating the XY sex determination mechanism in M. armatus. This study measured the morphological characteristics of male and female M. armatus and found that males were significantly superior to females in body weight and nearly all morphological indices. Subsequently, whole-transcriptome sequencing was performed on the gonads of adult males and females, identifying 11,714 DEmRNAs, 3442 DElncRNAs, 416 DEcircRNAs, and 620 DEmiRNAs, including male sex differentiation genes such as Sox30, Tbx1, Sox9, and Gata4, and female sex differentiation genes like Sox3, Foxl2, and Wnt4a. Functional enrichment analysis identified pathways associated with sex differentiation, including the TGF-beta signaling pathway, the steroid hormone biosynthesis, the Hippo signaling pathway, and the Wnt signaling pathway, etc. A ceRNA network was constructed based on differentially expressed mRNAs and ncRNAs, revealing that the sex differentiation-related genes Sox3, Sox9, Sox30, Tbx1, and Wt1 are regulated by one or multiple pairs of lncRNA/circRNA-miRNA pairs. The study results will provide molecular targets for research on sex-controlled breeding in M. armatus and lay an important theoretical foundation for clarifying its sex differentiation mechanisms. Full article

The substitution of fish meal with soybean meal (SBM) in aquafeeds aligns with sustainable development but often leads to depressed feed intake and growth in fish. This study aimed to investigate the mitigating effect of earthworm powder (EP) on these negative impacts in rice field eels (Monopterus albus), focusing on appetite regulation, intestinal health, and gut microbiota. Three isonitrogenous (~41% crude protein) and isolipidic (~6.4% crude lipid) diets (control [CON], high-SBM [SBM], and SBM + 2.5% EP [EP]) were tested in a 56-day trial. Juveniles (initial weight 18.00 ± 0.01 g) were stocked at 40 fish per net (0.5 m × 0.5 m× 0.5 m) and fed to visual satiety once daily. The results indicated that EP improved growth performance through a dual mechanism. Firstly, it was associated with significantly increased feed intake, correlated with the upregulated expression of orexigenic genes (agrp, npy) in the brain, and associated with reduced levels of anorexigenic hormones (Cholecystokinin, Leptin). Secondly, it correlated with enhanced intestinal health, evidenced by improved morphology (villus height, goblet cells), improved digestive enzyme activity, enhanced antioxidant capacity (increased Catalase and Superoxide Dismutase activities), repaired intestinal barrier function (upregulated zo-1, cla-12), and alleviated intestinal inflammation (downregulated tnf-α, il-1β). Furthermore, EP supplementation was associated with a shift in gut microbiota, including the suppression of the potential pathogen g_Clostridium_T and promotion of the beneficial bacterium g_Lactococcus_A, alongside increased concentrations of major short-chain fatty acids (acetate, propionate, and butyrate). These correlative observations suggest that EP may help mitigate the growth-inhibiting effects of SBM in Monopterus albus, offering a potential functional strategy for high-SBM aquafeeds. Full article

The microstructure and ultrastructure of the sperm of Japanese eel, Anguilla japonica, artificially induced with weekly injections with carp pituitary (CP) and human chorionic gonadotropin (HCG), was studied, and milt from 10 out of 20 mature fish was collected. Two distinct morphological structures of A. japonica sperm had been observed with optical microscopy. The cell nucleus of one type of sperm was round or nearly round, the sperm was smaller in size, with 2.57 ± 0.62 μm of the long diameter of the cell nucleus, 2.11 ± 0.59 μm of the short diameter, and 37.35 ± 7.71 μm of the flagellum length. Another type was the eyebrow-shaped sperm, the sperm was relatively larger in size, with 7.66 ± 1.09 μm of the long axis, 2.54 ± 0.46 μm of the short axis, and 38.26 ± 9.02 μm of the flagellum length. By means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the anterior end of the round sperm lacked an acrosomal structure. The implantation fossa was located in the center of the base of the sperm head, and it was in the shape of a channel along the long axis of sperm. The centriolar complex was situated within the implantation fossa. There were 2–3 mitochondria distributed at the basal end of the nucleus. Sperm flagellum prolongated from the sleeve cavity, and the initial part of axoneme connected to the distal end of basal body. The axoneme displayed a typical “9 + 2” pattern. There was a spherical structure in the curving area for eyebrow-shaped sperm, and the axoneme formed a “9 + 0” pattern. The discovery of two different types of sperm in the Japanese eel has provided new perspectives for research on its artificial reproduction. Full article

Co/Fe layered double hydroxides (LDHs) are among the most promising materials for advanced industrial and energy applications. Controlling the synthesis conditions of LDH materials is thus crucial to precisely tailoring cation composition and distribution, thereby regulating surface charge, ion sorption, and electron transfer required for optimal chemical and electrochemical performance. Therefore, characterizing Co/Fe precipitates (chemical composition, purity, morphology, and crystallinity) is also required to further exploit their controlled properties. Thus, solids with Co/Fe cation ratios between 2/2 and 10/2 were synthesized under an air atmosphere, at pH 8 or 11.5. For the first time, multiscale physicochemical techniques (FTIR, TEM-EELS, SEM, AAS, TGA, CHN elemental analysis, and XRD complemented by Rietveld refinement) were used to provide a fully documented characterization of the structure, texture, purity, chemical composition, and thermal properties of Co/Fe LDH-based materials. The combined interpretation of data from these complementary techniques enabled the precise identification and chemical characterization of the mineralogical phases formed. Both acid–base and redox reactions govern the overall Co^II/Fe^III LDH formation process. Well-crystallized LDHs were synthesized, except for the 2/2 ratio at pH 11.5, which led to the formation of α-Co(OH)₂, γ-Fe₂O₃, and Co₃O₄ byproducts. A pH value of 8.0 provides valuable LDH materials made of quasi-hexagonal particles with diagonal lengths between 200 and 500 nm. Rietveld refining showed the presence of LDH phases in the range of 95–98%. Multiple local chemical analyses using EDX on chosen particles demonstrated pure 4/2 and 6/2 LDHs. For the 2/2 ratio, the cumulative mass fraction of two LDH-type products consistently reached 97%, distributed between Co/Fe 1.5/2 (71%) and Co/Fe 4/2 (29%). For the 10/2 ratio, only partial Co precipitation was observed, forming 95% Co/Fe LDH phases distributed between Co/Fe 10/2 (72%) and 7/2 (28%). Full article

Chinese rice-field eel rhabdovirus (CrERV), an emerging viral pathogen, causes massive death in rice-field eels (Monopterus albus), thus threatening the industry’s development. There is currently no established treatment strategy for CrERV. This study evaluated the anti-CrERV effects of schisandrin B (Sch B) in vitro and in vivo. The results indicated that Sch B at 20 mg/L could inhibit the expression of the CrERV G protein, with a maximum inhibition rate of 69.5%. Additionally, Sch B mitigated the nuclear damage and mitochondrial membrane potential decline induced by CrERV, thereby preserving cellular morphology. A time-of-addition study suggested that Sch B might exert its antiviral effects during the mid-stage of viral replication. In vivo, Sch B exhibited promising preventive and therapeutic effects against CrERV infection in rice-field eels, enhancing their survival rate by 57% and 51%, when added at 0.075% and 0.025%, respectively. Overall, the natural product Sch B was proven to have excellent anti-CrERV activity, with broad prospects for application in aquaculture. Full article

Micro-minerals are essential for fish, but traditional inorganic micro-minerals (IMM) have low bioavailability. This study evaluated coated inorganic micro-minerals (CIMM) in juvenile American eels under commercial recirculating aquaculture system (RAS) conditions. Three experimental groups (n = 3 tanks per group, stocking density: 138 fish/m³) were fed basal diets supplemented for 56 days with: 1000 mg/kg IMM (IMM group, providing Cu 7, Fe 200, Mn 30, Zn 70, I 1.6, Se 0.4, and Co 1.2 mg/kg diet), 1000 mg/kg CIMM (CIMM group I), or 500 mg/kg CIMM (CIMM group II). Compared to the IMM group, the CIMM group I demonstrated significantly enhanced growth performance, with the specific growth rate increasing by approximately 31.14%, higher whole-body content and retention of minerals (Ca, P, Cu, Fe, Mn, Zn), and superior intestinal health, as reflected by significantly increased activities of digestive enzymes (amylase and lipase), enhanced antioxidant capacity (elevated SOD and CAT, reduced MDA), and improved morphology (villi length and muscular thickness), an altered intestinal microbiota (increased relative abundance of Firmicutes and reduced relative abundance of Proteobacteria), and significant metabolomic alterations in purine metabolism and linoleic acid metabolism. The CIMM group II maintained growth performance, with no significant difference in WGR and SGR compared to the IMM group, while still showing significant improvements in feed intake and mineral retention (P, Cu, Fe, Zn), and antioxidant capacity. Collectively, this study not only confirms the efficacy of CIMM in commercial RAS but also reveals that the supplementation level previously shown to be effective in the laboratory (50% CIMM) is insufficient under commercial farming conditions, implying that the dietary micro-mineral requirements for juvenile American eels in commercial RAS may be higher than those established in laboratory settings. Full article

Chinese rice-field eel rhabdovirus (CrERV) is a serious epidemic pathogen of Chinese rice-field eel and causes severe economic losses to aquaculture. However, there are no commercial drugs presently available to control CrERV infection. Eugenol is a bioactive compound extracted from clove plants and exhibits potential antiviral activity. In the study, the antiviral activity of eugenol against CrERV was investigated in Chinese rice-field eel (Monopterus albus). Eugenol reached the highest inhibition rate of 96.6% at 40 mg/L in Chinese rice-field eel kidney cells (CrEK). Notably, eugenol exhibits antiviral activity by directly targeting CrERV and additionally confers prophylactic effects against infection via its action on CrEK cells. The results of exploring the viral invasion cycle demonstrated that eugenol primarily exerted its antiviral effect during the middle stage and late stage (12 h and 24 h) of viral infection. In addition, eugenol inhibited CrERV-induced apoptosis of CrEK cells, maintained mitochondrial membrane potential levels, maintained physiological cellular morphology and structure, and protected cells from loss of cellular morphology, formation of apoptotic vesicles, and cell fragmentation. For the in vivo study, eugenol increased the survival rate of CrERV-infected rice-field eel by 56% and 48%, in prevention experiments and treatment experiments, respectively. Concurrently, eugenol significantly reduced viral loads and induced the upregulation of anti-inflammatory and antioxidant genes, indicating its potential for immunoregulation. In summary, eugenol holds potential for both preventing and treating CrERV infections in the aquaculture context. Full article

Thermoelectric (TE) materials represent a critical frontier in sustainable energy conversion technologies, providing direct thermal-to-electrical energy conversion with solid-state reliability. The optimizations of TE performance demand a nuanced comprehension of structure–property relationships across diverse length scales. This review summarizes established and emerging spectroscopic and microscopic techniques used to characterize inorganic and polymer TE materials, specifically poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS). For inorganic TE, ultraviolet–visible (UV–Vis) spectroscopy, energy-dispersive X-ray (EDX) spectroscopy, and X-ray photoelectron spectroscopy (XPS) are widely applied for electronic structure characterization. For phase analysis of inorganic TE materials, Raman spectroscopy (RS), electron energy loss spectroscopy (EELS), and nuclear magnetic resonance (NMR) spectroscopy are utilized. For analyzing the surface morphology and crystalline structure, chemical scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) are commonly used. For polymer TE materials, ultraviolet−visible–near-infrared (UV−Vis−NIR) spectroscopy and ultraviolet photoelectron spectroscopy (UPS) are generally employed for determining electronic structure. For functional group analysis of polymer TE, attenuated total reflectance–Fourier-transform infrared (ATR−FTIR) spectroscopy and RS are broadly utilized. XPS is used for elemental composition analysis of polymer TE. For the surface morphology of polymer TE, atomic force microscopic (AFM) and SEM are applied. Grazing incidence wide-angle X-ray scattering (GIWAXS) and XRD are employed for analyzing the crystalline structures of polymer TE materials. These techniques elucidate electronic, structural, morphological, and chemical properties, aiding in optimizing TE properties like conductivity, thermal stability, and mechanical strength. This review also suggests future research directions, including in situ methods and machine learning-assisted multi-dimensional spectroscopy to enhance TE performance for applications in electronic devices, energy storage, and solar cells. Full article

The slender snipe eel Nemichthys scolopaceus Richardson, 1848 is cosmopolitan in tropical and temperate seas, inhabiting the mesopelagic and bathypelagic zone between 200 and 1000 m depth. It is known to be an active predator in the DSL (Deep Scattering Layer) and the NBA (Near Bottom Aggregation), feeding mostly on decapod and euphausiid crustaceans, and playing a central role in carbon fluxes through meso- and bathypelagic ecosystems. Despite its potential importance in the deep trophic web ecosystem, the trophic ecology of Nemichthys scolopaceus is not well known. The aim of this study was to start to fill this knowledge gap. A total of 35 specimens of N. scolopaceus caught through bottom trawling in the Mediterranean Sea were analyzed in the laboratory for stomach content composition. As expected, mainly decapod crustaceans were found, in particular Plesionika martia, Pasiphaea multidentata, Funchalia woodwardi, and Robustosergia robusta species. The degree of digestion of prey in the stomachs was high in all cases. Our findings seem to confirm the specialist diet of Nemichthys scolopaceus based on shrimp-like crustaceans. Full article

Previous studies performed on the European eel Anguilla anguilla showed changes in the morphology and physiology of several tissues after exposure to environmental cocaine concentrations. To better understand the model through which cocaine produced its effects on these tissues, we investigated whether there were alterations in the expression of cannabinoid CB1 receptor (CB1R). Indeed, the endocannabinoid system, and CB1R, regulate neurotransmission, neurodevelopment, embryonic development, reproduction, and the activity of the gastrointestinal system. CB1R has been detected in nervous and peripheral tissues in mammals, and orthologues of the mammalian CB1R are found throughout vertebrates including chicken, turtle, frog, and fish. Therefore, samples of gut, kidney, ovary, muscle, liver, skin, and gills from cocaine-exposed and non-exposed eels were processed for routine histology. Immunohistochemical analysis was carried out to evaluate the immunolocalization of the CB1R. Our results showed for the first time (1) the presence of CB1R in the peripheral tissues of the eel, and (2) statistically significant differences in the localization of CB1R in the gut, kidney, ovary, muscle, and liver of the eels exposed to cocaine, compared to controls. These results demonstrate the involvement of CB1R in cocaine effects and suggest its potential role as a biomarker of tissue alteration. Full article

Bulk heterojunction (BHJ) organic solar cells (OSCs) represent a promising technology due to their cost-effectiveness, lightweight design and potential for flexible manufacturing. However, achieving a high power conversion efficiency (PCE) and long-term stability necessitates optimizing the interfacial layers. Zinc oxide (ZnO), commonly used as an electron extraction layer (EEL) in inverted OSCs, suffers from surface defects that hinder device performance. Furthermore, the active control of its optoelectronic properties is highly desirable as the interfacial electron transport and extraction, exciton dissociation and non-radiative recombination are crucial for optimum solar cell operation. In this regard, this study investigates the sulfur doping of ZnO as a facile method to effectively increase ZnO conductivity, improve the interfacial electron transfer and, overall, enhance solar cell performance. ZnO films were sulfur-treated under various annealing temperatures, with the optimal condition found at 250 °C. Devices incorporating sulfur-doped ZnO (S-ZnO) exhibited a significant PCE improvement from 2.11% for the device with the pristine ZnO to 3.14% for the OSC based on the S-ZnO annealed at 250 °C, attributed to an enhanced short-circuit current density (J_sc) and fill factor (FF). Optical and structural analyses revealed that the sulfur treatment led to a small enhancement of the ZnO film crystallite size and an increased n-type transport capability. Additionally, the sulfurization of ZnO enhanced its electron extraction efficiency, exciton dissociation at the ZnO/photoactive layer interface and exciton/charge generation rate without altering the film morphology. These findings highlight the potential of sulfur doping as an easily implemented, straightforward approach to improving the performance of inverted OSCs. Full article

Clostridium butyricum, recognized as a probiotic, is widely distributed in the intestines of various animals. In this study, the C. butyricum strain YF1 was isolated from the intestine of the ricefield eel (Monopterus albus) using an anaerobic culture method and was identified through morphological, physiological, biochemical, and 16S rRNA sequence analyses. Notably, C. butyricum YF1 exhibited a rapid growth rate and was found to produce ten types of short-chain fatty acids, particularly high-yield acetic acid and butyric acid. Additionally, YF1 demonstrated a high tolerance to elevated temperatures (70 °C), bile salts (0.1% to 0.5%), artificial intestinal fluid, and artificial gastric fluid, while being sensitive to most antibiotics. Further whole-genome sequencing revealed that C. butyricum YF1 has a total genome size of 4,314,266 bp and contains 3853 coding genes. Specifically, 82 tRNAs, 21 rRNAs, 288 repeat sequences, 13 prophages, and two gene islands were detected. Moreover, gene function analysis indicated that the highest number of genes were annotated to metabolic processes, and the butyric acid metabolism pathway was found to be complete. Meanwhile, 598 virulence genes and 186 resistance genes were predicted. In conclusion, the findings from this study contribute to probiotic development and provide innovative approaches for the sustainable and healthy cultivation of ricefield eels. Full article