Search Results (30)

As consumer demand for quality fish products continues to rise, quality has become a key factor in market competition. Ecological aquaculture research is exploring various farming methods to balance high-quality demand with environmental protection. This study compared three aquaculture models—cage culture (CG), recirculating aquaculture (RAG), and rice–fish co-culture (RG)—by analyzing muscle quality (AOAC, GC-MS), intestinal microbiota (16S rRNA), and liver metabolism (LC-MS) to assess their effects on M. albus. In terms of muscle quality, the RG group showed increased levels of EPA and DHA, reduced muscle moisture and crude lipid content, and enhanced crude protein accumulation. The crude protein content was significantly higher in the RAG group than in the CG group (p < 0.05). The RG group also had the highest levels of total, essential, and umami amino acids, followed by the RAG and CG groups. In terms of intestinal microbiota, the RG group had the highest microbial diversity and stability, with increased abundance of Firmicutes and Bacteroidetes and decreased levels of Proteobacteria. Compared to the CG, the RAG group also showed increased microbial diversity and a reduction in pathogenic genera. Liver metabolomics analysis demonstrated that the RG group had significant advantages over the CG group in amino acid, lipid, and energy metabolism. The RAG group exhibited upregulation of glycerophospholipid metabolism and a decrease in oxidative stress marker levels. Overall, the RG group enhanced muscle quality and optimized intestinal and liver metabolism in M. albus. Full article

To evaluate the effects of different organic selenium sources on rice field eel (Monopterus albus), four isonitrogenous and isolipidic diets were tested: a control (no supplement) and four diets each supplemented with 0.24 mg/kg selenium as diselenoacetic acid (Se1), diselenopropionic acid (Se2), diselenobutyric acid (Se3), or diselenodibutyric acid (Se4). Rice field eels (initial body weight 18.43 ± 0.03 g) were fed for 60 days. The Se1 group showed significantly higher WGR and SGR than the control. Whole-body crude protein was significantly increased in the Se3 and Se4 groups, while crude lipid content was significantly decreased in Se1, Se3, and Se4 groups. Selenium concentrations in the liver and kidney were highest in the Se2 group. Serum AST and ALT activities were decreased in Se4. In the Se4 group, intestinal CAT, T-SOD, and GSH-PX activities were enhanced, along with upregulation of Gpx8, CAT, Nrf2, and Keap1. Hepatic CAT and GSH-PX increased in Se2 and Se4, with Gpx8 upregulated in Se1. Intestinal lipase activity was significantly increased in Se2. At the phylum level, Proteobacteria predominated. At the genus level, Cetobacterium predominated. In summary, diselenoacetic acid enhanced growth, while diselenopropionic acid and diselenodibutyric acid improved antioxidant defense and intestinal health in rice field eel. Full article

Rice-field eel (Monopterus albus) slices, an important aquatic product in Southeast Asia, are prone to spoilage and deterioration during cold chain storage. In this study, the effects of a composite preservative (ε-polylysine, Vitamin C (Vc), epigallocatechin gallate (EGCG), and phloretin) on the muscle quality (color, texture, water holding capacity (WHC)) of rice-field eel slices during refrigeration storage at 4 °C for up to 7 days was investigated, and the underlying mechanism was elucidated by the integrated microbiome and metabolomics, in addition to Elisa and Low-Field Nuclear Magnetic Resonance (LF-NMR). After 7 days of storage, the WHC, shear force, and a* decreased by 11.39%, 34.37%, and 49.20% in treated samples, and by 19.18%, 38.38%, and 54.87% in control samples, respectively. The addition of the composite preservative significantly increased Hexokinase, Pyruvate kinase, and Creatine kinase, while it decreased the total viable count (TVC), total volatile basic nitrogen (TVB-N), thiobarbituric acid reactive substance (TBARS), and Lactic acid. Preservative treatment maintained the moisture content of the eel slices during storage and prevented bright red oxymyoglobin from transforming into brown metmyoglobin. Microbiota composition (especially Pseudomonas) and metabolic pathways (including amino acid and its metabolites, nucleotide and its metabolite, and organic acid and its derivatives, etc.) were obviously altered by the preservative treatment. Pseudomonas, tryptophan-aspartic acid (Trp-Asp), D-Glucose 6-phosphate, Succinic Acid, Biliverdin 1, 5-Diaminopentane, and Tyramine, etc., are potential biomarkers for the quality changes of eel slices during refrigeration. These findings provide an in-depth understanding of the improvement of the eel slice quality during refrigeration storage by the composite preservative. Full article

The Asian eel, a medicinal and edible species, lacks systematic research on age-related nutritional and flavor dynamics. To optimize breeding strategies and product differentiation, this study systematically investigated the nutritional composition, flavor profiles, and physical properties of Asian eel muscles across five distinct growth stages (1, 3, 7, 11, and 22 years). Results showed that unsaturated fatty acids increased with age, while ω-3/ω-6 ratios peaked in 1-year-old eels. The levels of hydrolyzed essential amino acids were higher in the 3–11-year-old groups, contrasting with higher free amino acids in 1- and 22-year-old eels. Texture declined in hardness/chewiness but improved in resilience with age, linked to muscle fiber density and diameter. One–three-year-old eels exhibited compact muscle fibers and superior texture, while 7–22-year groups demonstrated functional lipid profiles (high docosahexaenoic acid and γ-aminobutyric acid, low cholesterol). These findings highlight age-specific quality traits: 1–3-year-old eels are suitable for fresh consumption, 3–11-year groups offer bioactive benefits, and 22-year-old eels serve as premium functional ingredients. The study provides a scientific basis for targeted breeding and market segmentation to enhance the value of eel aquaculture. Full article

To investigate the dietary effects of Astragalus polysaccharides (APSs) on the growth performance, lipid metabolism, antioxidant activity, and non-specific immunity of Asian swamp eel (Monopterus albus) during the domestication stage, fish were randomly allocated into quadruplicate groups receiving Tenebrio molitor-based diets supplemented with Astragalus polysaccharides (APSs) at graded concentrations of 0 (CON), 700 (APS1), 1400 (APS2), and 2100 (APS3) mg/kg body weight for 28 days. The results showed that dietary APSs at 700–1400 mg/kg·bw significantly enhanced the weight gain rate (WG) and decreased the feed conversion ratio (FCR) of M. albus (p < 0.05). Concurrently, hematological analysis revealed that hemoglobin levels increased by 19.9% and 23.0% in the 700 and 1400 mg/kg APS groups, respectively (p < 0.05). In terms of lipid metabolism, supplementation with APSs significantly increased the serum high-density lipoprotein (HDL) content in all treatment groups (p < 0.05). Lower serum triglyceride (TG) levels were found in the APS2 group (p < 0.05), and decreased triglyceride (TG), cholesterol (CHO), and low-density lipoprotein (LDL) levels were displayed in the APS3 group (p < 0.05). Among the antioxidant parameters, the supplementation with 700 mg/kg·bw APSs significantly increased the glutathione peroxidase (GSH-Px) and catalase (CAT) activity levels of M. albus (p < 0.05). The APS2 group had a significantly increased total antioxidant capacity (T-AOC) and CAT activity levels (p < 0.05), and the APS3 group had significantly increased CAT activity levels (p < 0.05). In addition, the APS1 and APS3 groups had significantly reduced malondialdehyde (MDA) levels (p < 0.05). In terms of non-specific immunity, the APS1 and APS2 groups showed significantly increased superoxide dismutase (SOD) and lysozyme (LZM) activity levels of M. albus (p < 0.05), and the addition of 700 mg/kg·bw APSs significantly increased the levels of alkaline phosphatase (AKP) activity (p < 0.05). Furthermore, the levels of acid phosphatase (ACP) activity were significantly increased in all experimental groups (p < 0.05). In conclusion, the optimal APS addition for T. molitor as biocarrier bait is 700 mg/kg, corresponding to 352 mg/kg, which elicits improvements in the growth parameters, lipid homeostasis regulation, oxidative stress mitigation, and innate immune potentiation of M. albus during the domestication stage. Full article

The rising scarcity and cost of fishmeal due to overfishing and environmental challenges demand alternatives. Black soldier fly (Hermetia illucens) larvae (BSFL) meal, with its nutritional value, shows promise as a sustainable supplement for aquaculture species. This study evaluated the effects of BSFL meal supplementation on growth performance, survival, feed conversion efficiency, and meat quality in juvenile swamp eels (Monopterus albus) initially weighing 4.0 ± 0.5 g. The eels were fed diets with 0% (control), 10%, 30%, and 50% BSFL meal for three months. Growth performance was assessed using the absolute growth rate (AGR) and the specific growth rate (SGR). Feed conversion ratios (FCRs), survival rates, and meat quality metrics, including fillet percentage, crude protein, and moisture content, were analyzed. Statistical differences among groups were evaluated using one-way ANOVA followed by Tukey’s post hoc test for pairwise comparisons. The 30% BSFL group exhibited superior performance, achieving the highest AGR and SGR (p < 0.05) and the lowest FCR (2.33 ± 0.03). Fillet percentage was highest in this group (27.3% ± 0.7%), with no significant differences in crude protein or moisture content. Survival rates were consistent across treatments (75.2–76.0%, p > 0.05). These results confirm that 30% BSFL supplementation optimally enhances productivity and meat quality in swamp eels, highlighting BSFL meal’s potential as a sustainable aquafeed alternative. 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

Monopterus albus is a protogynous hermaphroditic fish that changes from female to male, but the underlying sex change mechanism remains as-yet unknown. In this study, we firstly cloned and characterized the sequence and protein structure of unc-13d of M. albus. We found that the genomic structure of unc-13d was different from other species. Expression was detected in the developing gonad by applying qRT-PCR and in situ hybridization. We found that the expression of unc-13d in the ovotestis was higher than in the ovary and testes. A strong signal of unc-13d was detected in oocytes and granulosa cells in the ovary and spermatogonia and primary spermatocytes in the testes. We found that the promoter methylation of unc-13d was negatively correlated with gene expression in developing gonads, especially at site 114. A dual-luciferase assay was designed and revealed that dmrt1 regulates promoter activity opposite to foxl2. In summary, during sex reversal, DNA methylation affects the binding of the transcription factor dmrt1 and foxl2 in the promoter region through methylation and demethylation interactions to regulate the expression of unc-13d during gonadal development. Full article

To investigate the dietary effects of chlorogenic acid (CGA) on the growth performance, lipid metabolism, antioxidant activity, and non-specific immunity of Asian swamp eel (Monopterus albus) during the domestication stage, a 28-day feeding experiment was conducted to supplement with CGA at levels of 0 (Cont.), 250 (CGA 0.50%), 500 (CGA 1.00%), and 750 (CGA 1.50%) mg/kg·bw by feeding with yellow mealworm (Tenebrio molitor). Compared with the control group, the addition of 250–750 mg/kg of CGA significantly increased the weight-gain rate (WG) of M. albus, and the CGA 1.0% group displayed the highest value. The content of hemoglobin and high-density lipoprotein in all CGA groups was markedly elevated (p < 0.05), while the triglyceride, glucose, low-density lipoprotein, and glycosylated serum protein levels were lowered (p < 0.05). Among the antioxidant enzymes, the glutathione peroxidase and catalase activity was significantly higher in all experimental groups than that of the control group, whereas the malondialdehyde activity was significantly reduced (p < 0.05). For a non-specific immune enzyme system, the lysozyme and alkaline phosphatase activity in all treatments and the superoxide dismutase and acid phosphatase activity in the CGA 0.5% group was markedly increased (p < 0.05). In conclusion, supplementation with CGA can enhance the growth performance and improve the lipid metabolism, antioxidant capacity, and non-specific immunity of M. albus during the domestication stage, and the optimal CGA supplementation for T. molitor as biocarrier bait is 500 mg/kg, corresponding to 405 mg/kg. Full article

Parasitic infestations present significant threats to the physiological health and ecological stability of aquatic species, frequently compromising immune defenses and elevating mortality rates. This study was conducted to elucidate the non-specific immune responses induced by Pallisentis (Neosentis) celatus infection in Monopterus albus, with a focus on intestinal histopathology and transcriptome gene expression. A histopathological examination revealed minor alterations in intestinal villi under low-level infection. A transcriptome analysis, performed using Illumina sequencing technology, identified 347 upregulated and 298 downregulated genes involved in critical biological pathways, such as lipid metabolism, immune responses, and the regulation of inflammatory processes. GO and KEGG analyses indicated the upregulation of immune-related pathways, including the RIG-I-like and IL-17 signaling pathways, highlighting a robust intestinal immune response. Conversely, the complement pathway was found to be downregulated, with significant suppression of C9, suggesting that the parasite may engage in immune evasion. Fluorescein-labeled C9 antibody assays confirmed reduced complement C9 levels in the infected tissues. A real-time PCR analysis identified the differential expression of eight genes, including C5, maats1, CFI, and gmnc, which were consistent with the sequencing results. These findings suggest that Pallisentis (Neosentis) celatus infection compromises intestinal health, induces inflammation, and activates non-specific immune responses in Monopterus albus. However, Pallisentis (Neosentis) celatus appears to evade the host immune response by suppressing the activation of complement components, thereby facilitating its reproductive parasitism. Full article

In mammals, 17-beta hydroxysteroid dehydrogenase 2 (Hsd17b2) enzyme specifically catalyzes the oxidation of the C17 hydroxyl group and efficiently regulates the activities of estrogens and androgens to prevent diseases induced by hormone disorders. However, the functions of the hsd17b2 gene involved in animal sex differentiation are still largely unclear. The ricefield eel (Monopterus albus), a protogynous hermaphroditic fish with a small genome size (2n = 24), is usually used as an ideal model to study the mechanism of sex differentiation in vertebrates. Therefore, in this study, hsd17b2 gene cDNA was cloned and its mRNA expression profiles were determined in the ricefield eel. The cloned cDNA fragment of hsd17b2 was 1230 bp, including an open reading frame of 1107 bp, encoding 368 amino acid residues with conserved catalytic subunits. Moreover, real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) analysis showed that hsd17b2 mRNA expressed strongly in the ovaries at early developmental stages, weakly in liver and intestine, and barely in testis and other tissues. In particular, hsd17b2 mRNA expression was found to peak in ovaries of young fish and ovotestis at the early stage, and eventually declined in gonads from the late ovotestis to testis. Likewise, chemical in situ hybridization results indicated that the hsd17b2 mRNA signals were primarily detected in the cytoplasm of oogonia and oocytes at stage I–II, subsequently concentrated in the granulosa cells around the oocytes at stage Ⅲ–Ⅳ, but undetectable in mature oocytes and male germ cells. Intriguingly, in ricefield eel ovaries, hsd17b2 mRNA expression could be significantly reduced by 17β-estradiol (E2) or tamoxifen (17β-estradiol inhibitor, E2I) induction at a low concentration (10 ng/mL) and increased by E2I induction at a high concentration (100 ng/mL). On the other hand, both the melatonin (MT) and flutamide (androgen inhibitor, AI) induction could significantly decrease hsd17b2 mRNA expression in the ovary of ricefield eel. This study provides a clue for demonstrating the mechanism of sexual differentiation in fish. The findings of our study imply that the hsd17b2 gene could be a key regulator in sexual differentiation and modulate sex reversal in the ricefield eel and other hermaphroditic fishes. Full article

The present study aimed to systematically investigate the underlying differences in flesh quality between wild and farmed Monopterus albus. Fifteen healthy M. albus per group with an average body weight of 45 g were sampled to analyze muscle parameters by biochemical indicators, histomorphology, and molecular biology. Compared with the wild fish, the farmed M. albus in flesh had lower crude protein, collagen, lysine, histidine, total amino acids, SFA, n-3 PUFA contents, and n-3/n-6 ratio (p < 0.05), and higher moisture, crude lipid, crude ash, MUFA, n-6PUFA, and total PUFA contents (p < 0.05). The thawing loss, drip loss, steaming loss, and boiling loss in the farmed group were significantly higher, and hardness, springiness, cohesiveness, gumminess, chewiness, and resilience were significantly lower than those in the wild group (p < 0.05). In addition, higher muscle fiber density and lower muscle fiber diameter were observed in wild M. albus (p < 0.05). In muscle transcriptome profiling, differentially expressed genes and enriched pathways are primarily associated with muscle development, protein synthesis, catabolism, lipid metabolism, and immunity. To the best of our knowledge, this is the first investigation that compares the flesh quality between wild and farmed M. albus in terms of biochemistry, histology, and molecular biology levels. Overall, wild M. albus had a higher nutritional value and texture quality than farmed M. albus. Full article

The effects of herbicides on non-target organisms in paddy fields have become a popular research topic. As a widely used herbicide, it is necessary to explore the potential toxicity of metamifop in non-target organisms, especially aquatic animals, in co-culture mode. In the present study, we evaluated the effects of metamifop (0, 0.2, 0.4, 0.6, and 0.8 mg/L) on the defense system (antioxidation, immunity, and apoptosis) in Monopterus albus. Reactive oxygen species (ROS) production, malondialdehyde (MDA) content, and protein carbonylation (PCO) increased significantly (p < 0.05) with the increasing metamifop concentration, resulting in oxidative damage. In the antioxidant system, superoxide dismutase (SOD) and catalase (CAT) activities increased significantly (p < 0.05) in the 0.2 mg/L treatment group compared with the control group, and decreased in 0.4, 0.6, and 0.8 mg/L treatment groups. Glutathione peroxidase (GPX) activity decreased significantly (p < 0.05) with the increasing metamifop concentration. In the immune system, white cell number (WCN) increased significantly (p < 0.05) in 0.2 mg/L treatment group, and then decreased with the increase in metamifop concentration. Compared with control group, acid phosphatase (ACP) activity not only increased significantly (p < 0.05) in 0.2 mg/L treatment group, but also decreased significantly (p < 0.05) compared with the increase in metamifop concentration. However, in all treatment groups, alkaline phosphatase (AKP) activity was significantly lower than that in the control group (p < 0.05). In the inflammatory response, TNF-α and IL-1β expression levels in the NF-κB signaling pathway decreased significantly (p < 0.05) with the increase in metamifop concentration, while IL-8 expression level in the same signaling pathway increased significantly (p < 0.05) in treatment groups. The expression levels of genes related to apoptosis showed that apoptosis was promoted after exposure to metamifop. The results of the present study show that metamifop induced oxidative damage via a high level of ROS production, and then inhibited or damaged the defense systems of M. albus. Full article

Forkhead box H1 (FoxH1) is a sexually dimorphic gene in Oreochromis niloticus, Oplegnathus fasciatus, and Acanthopagrus latus, indicating that it is essential for gonadal development. In the present study, the molecular characteristics and potential function of FoxH1 and the activation of the cyp19a1a promoter in vitro were evaluated in Monopterus albus. The levels of foxh1 in the ovaries were three times higher than those in the testes and were regulated by gonadotropins (Follicle-Stimulating Hormone and Human Chorionic Gonadotropin). FoxH1 colocalized with Cyp19a1a in the oocytes and granulosa cells of middle and late vitellogenic follicles. In addition, three FoxH1 binding sites were identified in the proximal promoter of cyp19a1a, namely, FH1 (−871/−860), FH2 (−535/−524), and FH3 (−218/−207). FoxH1 overexpression significantly attenuated the activity of the cyp19a1a promoter in CHO cells, and FH1/2 mutation increased promoter activity. Taken together, these results suggest that FoxH1 may act as an important regulator in the ovarian development of M. albus by repressing cyp19a1a promoter activity, which provides a foundation for the study of FoxH1 function in bony fish reproductive processes. Full article

Bmpr2 plays a central role in the regulation of reproductive development in mammals, but its role during ovarian development in fish is still unclear. To ascertain the function of bmpr2 in ovarian development in the ricefield eel, we isolated and characterized the bmpr2 cDNA sequence; the localization of Bmpr2 protein was determined by immunohistochemical staining; and the expression patterns of bmpr2 in ovarian tissue incubated with FSH and hCG in vitro were analyzed. The full-length bmpr2 cDNA was 3311 bp, with 1061 amino acids encoded. Compared to other tissues, bmpr2 was abundantly expressed in the ovary and highly expressed in the early yolk accumulation (EV) stages of the ovary. In addition, a positive signal for Bmpr2 was detected in the cytoplasm of oocytes in primary growth (PG) and EV stages. In vitro, the expression level of gdf9, the ligand of bmpr2, in the 10 ng/mL FSH treatment group was significantly higher after incubation for 4 h than after incubation for different durations. However, bmpr2 expression in the 10 ng/mL FSH treatment group at 2 h, 4 h and 10 h was significantly lower. Importantly, the expression level of bmpr2 and gdf9 in the 100 IU/mL hCG group had similar changes that were significantly decreased at 4 h and 10 h. In summary, Bmpr2 might play a pivotal role in ovarian growth in the ricefield eel, and these results provide a better understanding of the function of bmpr2 in ovarian development and the basic data for further exploration of the regulatory mechanism of gdf9 in oocyte development. Full article