Search Results (493)

Monopterus albus (Asian swamp eel) is a commercially important, air-breathing freshwater fish harvested throughout East and Southeast Asia. As a protogynous species, it begins life as a female, passes through a transitional phase, and ultimately becomes male, making sexual-state classification difficult and potentially affecting management in capture fisheries and aquaculture. We examined sex–size relationships in market-purchased, reportedly wild-caught M. albus from northern and northeastern Thailand using gonadal histology to determine sexual state, together with body length (BL), body mass (BM), and a separate otolith-aged sample. Among 199 histologically examined individuals, no females were observed above approximately 70 cm BL or 270 g BM. Across much of the intermediate size range, female, transitional, and male individuals overlapped in size. Transitional individuals reached 78 cm and 424 g, showing that the upper values represent female-exclusion boundaries rather than thresholds identifying males. No male was smaller than 55 cm BL or 200 g BM, although sampling below these values was sparse. Otolith-derived age estimates from a separate sample of 70 eels provided local size-at-age context but could not establish age at sex transition because sexual state was not determined in those individuals. Comparisons with published studies showed substantial regional variation in size–sex relationships, indicating that size-based criteria developed in one region may not transfer reliably elsewhere. The boundaries identified here provide practical guidance for fisheries monitoring and broodstock selection in northern and northeastern Thailand while emphasizing the need for locally validated criteria elsewhere. Full article

The Japanese eel (Anguilla japonica) is an economically important aquaculture species, but cellular mechanisms underlying sex steroid responses remain poorly characterized. In this study, we established and characterized a continuous brain-derived cell line from Japanese eel, designated AJBC. The cells exhibited stable fibroblast−like morphology and continuous proliferation. Molecular characterization showed high expression of col1a1, a marker associated with fibroblast−like stromal populations, whereas neuronal and glial markers (map2, gfap, and sox2) showed low expression. The neural-associated marker nestin was detectable, indicating that AJBC cells retained certain brain-associated characteristics. AJBC cells were successfully transfected with a GFP−expressing plasmid, demonstrating their potential for genetic manipulation. Transcriptome analysis identified 3212 and 3522 differentially expressed genes following 17β−estradiol (E2) and 11-ketotestosterone (11−KT) treatment, respectively. KEGG analysis revealed enrichment of PI3K−Akt and MAPK signaling pathways, as well as cell adhesion and cytoskeletal-related processes. Representative reproductive-related genes, including sox9 and foxl2, showed differential expression following sex steroid hormone treatment. E2 increased esr1 and esr2 expression, whereas 11−KT increased ar expression, confirming the steroid-responsive characteristics of AJBC cells. This brain-derived cell line provides a useful in vitro model for investigating sex steroid−responsive molecular mechanisms and neuroendocrine-related processes in Japanese eel. Full article

KDF (potassium diformate) has been recognized as a highly promising additive due to its beneficial effects on growth and immunity improvement. In order to expand the application of KDF in the aquatic farming practice, the effects of KDF on ricefield eels were thoroughly evaluated. In the present study, the growth performance, blood biochemistry, hepatic health and disease resistance were assessed in the juvenile ricefield eels fed diets supplemented with 0 (D0), 3 (D1), 6 (D2), 9 (D3), 12 (D4) and 15 (D5) g/kg KDF. After 8 weeks feeding, fish weight gain rate (WGR) was improved by KDF addition, and the estimated optimum dietary KDF was determined at 8.91 g/kg according to the regression analysis between dietary KDF level and WGR. Fish condition factor (CF) was increased by dietary KDF supplementation compared to the control (D0). The VSI of fish decreased significantly and then kept stable when the dietary KDF level was above 9 g/kg (p < 0.05). The supplementation of KDF in diet had no significant effect on the moisture, crude ash, and crude protein contents of the whole fish (p > 0.05), while the crude lipid content in the D4 group was significantly lower than that in the control (p < 0.05). Compared to the control group, the inclusion of 9 g/kg KDF (D3) in the diet significantly decreased serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) (p < 0.05). Liver catalase (CAT) activity increased significantly with increasing the level of KDF in diet, but it remained stable at KDF levels at and above 9 g/kg (D3) (p < 0.05). The significant improvement of glutathione peroxidase (GSH-Px) activity and total antioxidant capacity (T-AOC) were found in the D1 and D4 groups, respectively (p < 0.05). Liver malondialdehyde (MDA) content showed a non-monotonic pattern across KDF levels, and the addition of KDF in diet did not significantly alter MDA content compared to the control (p > 0.05). Fish in the D4 group showed the lowest liver malondialdehyde (MDA) content. Serum ALP activity was markedly elevated in the D3 group compared with the control (p < 0.05). Supplementation of KDF in diets enhanced hepatic ALP and ACP activities, which differed significantly from the control in the D3 and D4 groups, respectively (p < 0.05). The histological results indicated that while no significant alteration of liver cell structure was observed, fish liver showed a lower number and size of lipid droplets with the KDF level increasing, and the hepatic sinusoids appeared more prominent in the high KDF group (D5). The Aeromonas hydrophila challenge test demonstrated that the addition of 9 g/kg KDF (D3) in fish diet significantly increased the survival rate of juvenile ricefield eel (p < 0.05). In summary, dietary supplementation with KDF significantly enhanced growth performance, improved several biomarkers associated hepatic health, and strengthened pathogen resistance in juvenile ricefield eels. Full article

The striped eel catfish Plotosus lineatus is a venomous Indo-Pacific species that has rapidly expanded within the Mediterranean Sea following its Lessepsian migration through the Suez Canal. Understanding its current distribution and future invasion potential is essential for evaluating ecological risks under ongoing climate change. In this study, ensemble species distribution models were applied to predict the present and future habitat suitability of P. lineatus across the Mediterranean Sea under the CMIP6 SSP2-4.5 climate scenario. Georeferenced occurrence records were compiled from published literature and validated databases. A total of 21 environmental variables were initially evaluated, and after multicollinearity filtering using Pearson correlation (|r| < 0.7) and Variance Inflation Factor (VIF < 10) analyses, 11 environmental predictors obtained from the Bio-ORACLE v3 database were retained for modelling. Nine modelling algorithms were initially evaluated, and six high-performing models were integrated into the final unweighted ensemble model based on predefined AUC and TSS performance criteria. Minimum seawater temperature was identified as the dominant factor controlling habitat suitability, indicating that winter thermal conditions currently represent the principal ecological barrier limiting the Mediterranean distribution of the species. Current projections identified the Levantine Basin as the principal invasion hotspot. Future projections, based on mean environmental conditions for the 2020–2100 period under the CMIP6 SSP2-4.5 scenario, indicated a substantial increase in suitable habitats toward the central Mediterranean, including southern Italy and the Aegean region. These findings suggest that future climatic conditions may facilitate the expansion of P. lineatus into additional areas of the Mediterranean Sea, highlighting the need for continued monitoring and regional management. Full article

This study compared conventional aquaponics (AP), biofloc-based aquaponics (FLOCponics, FP), and hydroponics (HP) in terms of juvenile eel (Anguilla japonica) growth, ‘Caipira’ lettuce (Lactuca sativa) productivity, and water-quality characteristics. The AP and FP treatments each comprised three replicate fish tank–plant cultivation systems stocked with 119 eels per tank, whereas HP was included as a control for plant production. Eels reared in FP exhibited a higher estimated final biomass and specific growth rate and a lower feed conversion ratio than those reared in AP. The total and shoot biomass of lettuce were higher in FP than in AP and were comparable to those obtained in HP. Full article

Mitigating flood risk and planning river corridors in Torrent-type Basins (TBs) requires integrated frameworks that link hydro-geomorphological processes with ecological quality, a combination currently lacking in regional planning. This study presents an integrated hydro-geomorphological and ecological analysis of the Rio Geremeas catchment (Sardinia, Italy), developed within the Regional Sediment Management Plan (PGS). The approach combines multi-scale geomorphological mapping, the IDRAIM eco-morphological framework, and 2D hydro-morphodynamic modelling (MIKE 21C), supported by field surveys and remote sensing of sediment source areas and biological assemblages (riparian vegetation, macroinvertebrates, and fish). Results reveal a direct link between altered sediment dynamics and ecological degradation, with confined reaches showing lower biotic diversity compared to mobile, morphologically functional reaches. 50-year flood simulations identified critical erosion/deposition zones, guiding targeted proposals: restoring sediment continuity by removing hydraulic constraints, controlling invasive species, and managing the river mouth to favour the migration of the European eel. This work provides a transferable, interdisciplinary approach for sediment- and ecosystem-informed river basin planning, directly supporting the EU Water Framework Directive and climate resilience strategies. Full article

Taiwan’s Japanese eel (Anguilla japonica) aquaculture industry has historically developed as an export-oriented sector supplying the Japanese market but has undergone structural changes under declining glass eel availability. This study integrates long-term fisheries statistics, aquaculture production data, international trade records, and policy documents to examine the sustainability challenges facing Taiwan’s eel industry during 2004–2023. Descriptive statistics, Ordinary Least Squares (OLS) regression, trade analysis, and policy analysis were employed to examine the interactions among glass eel supply, aquaculture production, export development, and regional governance. The results reveal three major findings. First, declining glass eel availability has become a significant constraint on aquaculture production, and OLS regression confirms a significant positive relationship between glass eel supply and subsequent cultured eel production. Second, despite declining production and exports of market-size eels, Taiwan’s eel industry has undergone structural adjustment, characterized by increasing domestic market importance and the expansion of juvenile eel exports. Third, although regional governance has focused on stocking quotas, actual stocking volumes in Taiwan remain far below permitted levels, indicating that limited resource availability, rather than regulatory restrictions, has become the principal constraint, while discrepancies among catch, stocking, and trade statistics highlight limitations in current monitoring systems. Overall, as international attention to the conservation and sustainable management of Japanese eel resources continues to grow, effective governance will increasingly depend on cooperation among the major producing and trading economies in East Asia. Improving transparency in cross-border resource flows, strengthening information exchange, and enhancing regional collaboration will be essential for the long-term sustainability of the Japanese eel industry. Full article

To date, four species of the genus Edwardsiella—E. tarda, E. ictaluri, E. piscicida, and E. anguilarum—have been identified as the cause of disease and mortality in various fish species. Thirty-six Edwardsiella strains isolated from different fish species in the Netherlands were identified using multilocus sequence analysis (MLSA) based on sequence analysis of the genes gyrB, pgi and phoU. In parallel, an Edwardsiella matrix-assisted laser desorption ionization–time-of-flight mass spectrometry (MALDI-TOF MS) database was created by analyzing peptide spectra of a subset of these strains belonging to the four fish pathogenic species. MALDI-TOF MS analysis of the Edwardsiella isolates using the newly created database revealed 100% agreement with results of MLSA. Moreover, the presence of each Edwardsiella species was associated with specific fish host and source, with E. piscicida being the dominant species in Dutch aquaculture. In addition, a novel strain was isolated from electric eel, genetically diverging from the four established species. Whole-genome comparisons of the novel strain with those species showed DNA-DNA hybridization and average nucleotide identity scores suggestive of a new species. In conclusion, both MLSA and MALDI-TOF analysis can be used to identify Edwardsiella species. Moreover, it has been observed that different Edwardsiella species show a preference for certain hosts or sources. Full article

The rice field eel (Monopterus albus) is an economically important aquaculture species widely distributed in Southeast Asia. However, the lack of nationally approved varieties and the increasing demand for high-quality eel products have highlighted the necessity of developing improved germplasm resources for aquaculture production. In this study, morphometric morphology and muscle texture traits were evaluated in 367 wild eel individuals, and a genome-wide association study (GWAS) based on whole-genome resequencing was conducted to identify genetic variants and candidate genes associated with economically important traits, including body length (BL), tail length (TL), tail height (TH), head length (HL), head width (HW), head height (HH), hardness, chewiness, springiness, and resilience. The GWAS identified three significant and seventeen suggestive SNPs associated with body shape traits, with most loci located on chromosome 4. Candidate gene analysis of the associated genomic regions revealed several candidate genes potentially associated with growth regulation, nutrient metabolism, and skeletal development, including b4galnt4a, tmem86a, cpt1b, mrpl23, lama1, gcm2, wnt3a, thrab, and bmpr1a. Additionally, four suggestive SNPs associated with muscle texture traits were detected, and candidate genes related to muscle development and extracellular matrix regulation, including fstl1b, col5a3a, and pnn, were identified. These findings provide new insights into the genetic basis underlying morphometric variation and muscle texture diversity in M. albus. The identified SNP markers and candidate genes provide potential molecular resources for understanding the genetic basis of body morphology and muscle texture variation in rice field eel. Full article

Fourteen novel antioxidant peptides were screened from the enzymatic hydrolysates of Asian swamp eel bone (ASEB) through an in silico analysis. Their ABTS and ORAC radical scavenging capacities were 1.70–4.29-fold and 2.79–5.90-fold higher than those of Trolox, respectively. Additionally, two novel peptide sequences (NVGW and WALN) were identified. Quantum chemical calculations combined with active–-site methylation experiments demonstrated that hydrogen atoms on tryptophan’s indole nitrogen, tyrosine’s phenolic hydroxyl, and arginine’s guanidinium group play crucial roles in enhancing ABTS and ORAC activities. Molecular docking further showed stable binding of ASEB peptides to myeloperoxidase (MPO) through hydrogen bonds and electrostatic interactions. Further studies indicated that ASEB alleviated oxidative stress in zebrafish by effectively reducing ROS accumulation, restoring redox homeostasis, and modulating the expression of Keap1–Nrf2 pathway-related antioxidant genes. These results enhance our understanding of the antioxidant properties of ASEB-derived peptides and support the high-value utilization of animal byproducts. Full article

The modulation of ZnO physicochemical properties through Mn doping represents a promising strategy for the development of multifunctional nanomaterials with enhanced biological performance. In this study, we investigate how the nominal Mn concentration influences both the physicochemical properties and antibacterial, antibiofilm, and anti-virulence activities of ZnO nanoparticles (NPs). Mn-doped ZnO nanoparticles containing nominal Mn from 2.5 to 10 mol% were synthesized through a simple wet-chemical approach and characterized by UV–Vis, Raman, TEM, EDX, and EELS analyses. The resulting ZnO-based NPs showed average dimensions of 3.7–4.8 nm, while increasing Mn incorporation produced measurable changes in optical response and morphology of nanoparticles. Antibacterial activity was evaluated against Gram-positive and Gram-negative bacterial models by assessing planktonic growth inhibition, biofilm formation, and pyocyanin production. The sample with the highest Mn amount (Mn₁₀-ZnO) markedly enhanced antibacterial performance by reducing MIC₉₀ from 150 to 37.5 μg/mL against Staphylococcus aureus and from 300 to 75 μg/mL for Pseudomonas aeruginosa. Mn doping also enhanced biofilm inhibition and produced a progressive reduction in pyocyanin synthesis. These results establish a concentration-dependent relationship between Mn concentration, nanoparticle properties, and antibacterial performance, highlighting the potential of Mn-doped ZnO nanoparticles for the development of anti-infective biomaterials, including antimicrobial coatings for implantable medical devices. Full article

To compare the fatty acid composition in different tissues of Anguilla japonica before and after sea entry, we analyzed the muscle, liver, and ovary of eels from the Yangtze Estuary and offshore waters, and describe the distribution patterns of various fatty acids in different tissues. Comparing different tissues, in eels from the estuary, the muscle had the highest content of EPA, the liver had the highest content of DHA, and the ovary had the highest contents of ARA. In offshore eels, the muscle had the highest contents of C16:1 and C18:1n9c; the liver had the highest content of C16:0; and the ovary had the highest contents of C18:0 and DPA3. Comparing eels before and after sea entry, the contents of C14:0, C16:0, C20:1n9 and C20:2 in the ovary of estuary eels were significantly higher than those in the offshore eels. Conversely, the contents of C18:0, C20:0, DPA3, HUFA, total n3-PUFA and n3/n6 ratio in the ovary of offshore eels were significantly higher than those in estuary eels. Ovaries of estuarine eels showed higher proportions of saturated fatty acids, whereas ovaries of offshore eels showed higher proportions of n3-PUFA. The observed differences in ovarian fatty acid profiles may reflect the nutritional demands associated with gonadal development stages, which were determined by histological oocyte staging. Full article

Shansha Bay, southeastern China, is a typical semi-enclosed bay facing intense anthropogenic pressure, with mariculture production reaching approximately 660,000 tons annually, predominantly driven by the large yellow croaker (Larimichthys crocea) industry. To assess how these pressures influence biodiversity detection, we employed eDNA metabarcoding targeting the 12S rRNA gene to survey fish diversity across 10 sites, integrating both surface water and sediment matrices. A total of 40 species belonging to 16 orders, 27 families and 32 genera, were identified. Among them, L. crocea, Bostrychus sinensis, Clupanodon thrissa and Siganus fuscescens are the dominate species, which comprised over half of all OTUs. Comparison with historical trawl surveys revealed 30 newly recorded species, including the Japanese eel (Anguilla japonica) and oarfish (Regalecus glesne). Alpha diversity was low (Shannon: 0.69–1.93), with significant spatial disparities driven by freshwater runoff and hydrodynamics. While eDNA effectively captured the dominance of cultured species like L. crocea, the extreme biomass signal poses challenges for detecting wild populations. Our findings underscore that a multi-matrix eDNA approach is crucial for accurate biodiversity assessments in aquaculture-dominated coastal ecosystems, although distinguishing wild stocks from aquaculture-derived DNA remains a critical methodological hurdle. Full article

Citrobacter freundii, an opportunistic Gram-negative bacterium belonging to the Enterobacteriaceae family, is emerging as a significant pathogen in diverse aquatic species, often associated with environmental stress and poor husbandry conditions. This study describes four distinct cases of fatal C. freundii-associated lesions in captive freshwater species in South Korea, including an Ocellate river stingray (Potamotrygon motoro), a Royal peacock bass (Cichla intermedia), a Japanese eel (Anguilla japonica), and a Poison dart frog (Dendrobates leucomelas). Bacterial DNA was analyzed using 16S rRNA PCR and sequence analysis, and FFPE tissues were additionally examined by PCR for molecular identification. Tissues were examined using routine hematoxylin and eosin (H&E) staining for detailed histopathology. Results: Molecular analysis detected C. freundii-associated DNA in the liver, kidney, and intestine of all samples. Histopathology consistently revealed severe bacterial enteritis with epithelial necrosis and abundant intraluminal bacterial aggregates (stingray, frog). Systemic manifestations included severe ulcerative skin lesions (peacock bass), hepatic fatty degeneration (peacock bass, eel), renal tubular degeneration (peacock bass), and prominent hepatic melanomacrophage center activation (frog); however, these findings should be interpreted as lesions observed in association with C. freundii detection, as several of these changes are not specific to bacterial infection. To our knowledge, this study provides one of the first comparative histopathological descriptions of naturally occurring C. freundii-associated cases across multiple captive freshwater vertebrate species in South Korea. Although bacterial culture, biochemical identification, and experimental infection were not performed, this retrospective investigation identified an association between molecular detection of C. freundii and histopathological lesions. Therefore, these findings should be interpreted as supportive diagnostic evidence rather than proof of a definitive causal relationship. These observations highlight the complementary value of histopathological examination alongside molecular detection in the diagnostic evaluation of aquatic animal diseases. Full article

The aim of this study is to investigate how external nutrient supply affects the allocation of reproductive energy during artificial ripening of American eels (Anguilla rostrata), as well as the physiological regulatory mechanisms involved in their bodies. Healthy female American eels were selected for the experiment and randomly divided into two groups: feeding group and starvation group (simulating the natural migration of American eels without eating). The initial weight of the feeding group was (308.43 ± 36.99 g), and the initial weight of the starvation group was (291.67 ± 63.31 g). The entire experiment was divided into two stages: the first stage was a 6-month nutritional reinforcement period, during which the feeding group was regularly fed with Vannamei shrimp, while the starvation group was not fed throughout the entire process. The second stage was a 3-month artificial ripening stage, during which both groups of eels stopped feeding. Inject 1 mL of mixed hormone (containing 6.5 mg of carp pituitary extract CPE+200 IU human chorionic gonadotropin HCG per mL per week) into each eel for a total of 12 injections to induce gonadal maturation. Both groups of eels did not die during the experiment, with a survival rate of 100%. As the gonads continue to develop and mature, the growth and development advantages of the feeding group of eels are very obvious: body weight, chest circumference, and gonadal index are significantly higher than those of the starvation group. After completing 12 hormone injections, the gonadal index of the feeding group reached (32.72 ± 7.01%), while that of the starvation group was only (4.35 ± 2.48%). Under artificial ripening conditions, the egg diameter of the feeding-eel group increased rapidly in the later stage of the experiment. The growth rate of eggs in the starvation group was slow, and the final egg diameter was significantly smaller. The diameters of the nuclei of both groups of oocytes increased synchronously with the progress of the experiment; the number of nucleoli in the feeding group first increased and then decreased, while the number of nucleoli in the starvation group continued to increase. The oil droplets inside both sets of eggs gradually increased in size, and the oil droplets fed to the eggs in the middle and late stages of maturation had a larger volume. Hormone test results showed that the testosterone (T) level in the eel fed group increased significantly in the later stage of the experiment. This indicates that adequate nutrition can alleviate the inhibition of the reproductive endocrine axis through positive feedback regulation of the pituitary gonad (BPG) axis. Nutritional reinforcement before ripening can promote gonadal development and enhance reproductive capacity by regulating the distribution of nutrients between muscles and gonads. The results of this study provide a solid theoretical basis for improving the nutritional management plan for parent fish in the fully artificial breeding process of American eels. Full article