Monopterus Albus Research Articles

Chromosome-Scale, Haplotype-Resolved Genome Assembly of Non-Sex-Reversal Females of Swamp Eel Using High-Fidelity Long Reads and Hi-C Data.

The Asian swamp eel (Monopterus albus) is an excellent model species for studying sex change and chromosome evolution. M. albus is also widely reared in East Asia and South-East Asia because of its great nutritional value. The low fecundity of this species (about 300 eggs per fish) greatly hinders fries production and breeding programs. Interestingly, about 3–5% of the eels could remain as females for 3 years and lay more than 3,000 eggs per fish, which are referred to as non-sex-reversal (NSR) females. Here, we presented a new chromosome-level genome assembly of such NSR females using Illumina, HiFi, and Hi-C sequencing technologies. The new assembly (Mal.V2_NSR) is 838.39 Mb in length, and the N50 of the contigs is 49.8 Mb. Compared with the previous assembly obtained using the continuous long-read sequencing technology (Mal.V1_CLR), we found a remarkable increase of continuity in the new assembly Mal.V2_NSR with a 20-times longer contig N50. Chromosomes 2 and 12 were assembled into a single contig, respectively. Meanwhile, two highly contiguous haplotype assemblies were also obtained, with contig N50 being 14.54 and 12.13 Mb, respectively. BUSCO and Merqury analyses indicate completeness and high accuracy of these three assemblies. A comparative genomic analysis revealed substantial structural variations (SVs) between Mal.V2_NSR and Mal.V1_CLR and two phased haplotype assemblies, as well as whole chromosome fusion events when compared with the zig-zag eel. Additionally, our newly obtained assembly provides a genomic view of sex-related genes and a complete landscape of the MHC genes. Therefore, these high-quality genome assemblies would provide great help for future breeding works of the swamp eel, and it is a valuable new reference for genetic and genomic studies of this species.

The Protective Effect of Mulberry Leaf Flavonoids on High-Carbohydrate-Induced Liver Oxidative Stress, Inflammatory Response and Intestinal Microbiota Disturbance in Monopterus albus

An 8-week feeding trial with high-carbohydrate- and 100, 200 and 300 mg/kg mulberry leaf flavonoids (MLF)-supplemented diets (HCF1, HCF2 and HCF3, respectively) was conducted to evaluate the protective effect of MLF on oxidized high-carbohydrate-induced glucose metabolism disorder, liver oxidative damage and intestinal microbiota disturbance in Monopterus albus. The results showed that HC diets had significant negative effects on growth, glucose metabolism, liver antioxidant and immunity, as well as intestinal microbiota, in comparison to CON diets. However, WGR and SR in the HCF3 group dramatically increased compared to the HC group. With the increase of MLF in the HC diet, the activities of glycolysis and antioxidant enzymes in the liver tended to increase, while the changes of gluconeogenesis-related enzyme activities showed the opposite trend and significantly changed in the HCF3 group. Additionally, MLF supplementation dramatically increased the mRNA expression involved in glycolysis, antioxidative enzymes and anti-inflammatory cytokines in comparison with the HC group. Furthermore, gluconeogenesis and pro-inflammatory cytokine genes’ expression dramatically decreased. Furthermore, the proportion of Clostridium and Rhodobacter in the HC group dramatically declined, and the proportion of Lactococcus dramatically increased, compared to the HC group. In addition, 300 mg/kg MLF supplementation significantly improved the species composition and homeostasis of intestinal microbiota. These results indicate that MLF can alleviate the negative effects of low growth performance, glucose metabolism disorder, liver oxidative damage and intestinal microbiota disturbance caused by HC diets, and the relief of MLF is dose-related.

Sanguinarine attenuates hydrogen peroxide-induced toxicity in liver of Monopterus albus: Role of oxidative stress, inflammation and apoptosis

In aquatic animals, hydrogen peroxide (H2O2), which is a source of oxidative stress, can cause physiological dysfunction, inflammation, and death. Sanguinarine (SAN) is a plant extract known to improve antioxidant and immune capacity. However, the roles of SAN in H2O2-induced liver tissue toxicity is unclear. The effects on hepatic oxidative damage, inflammatory response, and apoptosis were investigated by feeding rice field eel with 0, 375, and 750 μg/kg of SAN for eight weeks and then intraperitoneally injected with H2O2. The results showed that after 24 h of H2O2 injection, the activities of ALT and AST in serum were significantly increased, oxidative damage and inflammatory response occurred in the liver, and apoptosis was induced, which indicated that H2O2 induced liver damage in rice field eel. However, dietary supplemented with 375 or 750 μg/kg SAN significantly decreased the activities of ALT and AST in serum, and significantly increased the antioxidant function (decreased ROS, MDA, and antioxidant enzymes levels, downregulated antioxidant-related gene expression, and inhibited the transcription level of nrf2). The addition of SAN at 375 or 750 μg/kg ameliorated H2O2-induced inflammatory response of liver (upregulated tgf-β1 mRNA expression, downregulated il-1β, il-6, il-8, and il-12β mRNA expression, and inhibited the transcription levels of tlr-3 tlr-7, and nf-κb). In addition, dietary supplemented with 375 or 750 μg/kg SAN alleviated the apoptosis of liver induced by H2O2 (downregulated bax mRNA expression, upregulated caspase3 mRNA expression, and reduced the number of apoptotic cells by TUNEL staining). Overall, these results suggested that SAN could alleviate the liver injury in rice field eel induced by H2O2, mainly by improving antioxidant capacity, alleviating inflammatory response and inhibiting apoptosis, and the effect of 750 μg/kg SAN addition is better than 375 μg/kg.

Molecular characterization and expression analysis of IL-10 and IL-20L genes in swamp eel (Monopterus albus) against Aeromonas veronii infection

IL-10 cytokine family belongs to type Ⅱhelix cytokine, which has many common characteristics and different biological functions. In this paper, the IL-10 and IL-20L genes in the IL-10 family of swamp eel (Monopterus albus) were characterized for the first time, and their expression patterns after stimulation by Aeromonas veronii were studied. Through phylogenetic tree, amino acid sequence alignment and similarity analysis, eel IL-10 and IL-20 were the closest to their counterparts of tilapia, and fish IL-20L molecules were clustered into a branch alone, and then converged with IL-19/IL-20/IL-24 of higher vertebrates. There are two conserved motifs in eel IL-10 and IL-20L, and the motif in IL-10 is completely consistent with the conserved signature motif of IL-10 family. Eel IL-10 has 6 α helices and 4 conserved cysteines, and IL-20 has 5 α helices and 6 conserved cysteines, in which helix E′ is equivalent to helices E and F of IL-10. These results indicate that fish IL-10 and IL-20L cytokines were evolutionarily conservative. The gene structure of IL-10 and IL-20 of all selected species consists of five coding exons and four 0-phase introns, which are closely linked at the corresponding loci. Our study supports the hypothesis that the IL-20 subfamily cytokines share a common origin with IL-10. Whether it is tissue expression or induced expression, eel IL-10 has a higher expression level than IL-20L, but both of them may be involved in the late stage of the host's response to bacterial infection, and there are differences between them and other fish expression patterns. It is hoped that these research results will help to understand the immune system of fish and formulate disease prevention and control measures.

Transcriptomic analysis provides insights into the growth and maturation of ovarian follicles in the ricefield eel (Monopterus albus)

The ricefield eel is becoming an important aquaculture species in China. However, the regulation of oocyte growth and maturation in ricefield eels is poorly understood. In this study, the development of ricefield eel ovarian follicles was classified into nine stages, namely the primary growth/previtellogenic (PG/PV), early vitellogenic (EV), mid-vitellogenic (MV), late vitellogenic (LV), full-grown (GV0), germinal vesicle migration 1 (GV1), germinal vesicle migration 2 (GV2), germinal vesicle migration 3 (GV3), and germinal vesicle breakdown (GVBD) stages, which are based on follicle morphologies and sizes, vitellogenic states, and the positions of germinal vesicles. Comparative transcriptomic analysis was performed on isolated ovarian follicles from the MV to the GVBD stages. A total of 438,410 high-quality reads were obtained after filtering from six cDNA libraries of ovarian follicles at the MV, LV, GV0, GV1, GV2, and GVBD stages, 92.09% of which were perfectly mapped to the ricefield eel genome. Real-time PCR analysis showed that the expression profiles of 20 representative genes related to oocyte growth and maturation largely paralleled with those inferred from transcriptome data, which indicated the reliability of RNA-Seq data for gene expression analysis in the present study. The estradiol biosynthesis pathway was highly activated in ovarian follicles at the LV stage, which may be related to the stimulation of vitellogenin synthesis and/or meiotic arrest. The high expression of the Vtg receptor gene vldlr in ovarian follicles at MV and LV is consistent with active vitellogenesis at these stages. Thirteen cathepsin-encoding genes were highly expressed in ovarian follicles with different expression profiles during development from MV to GVBD, which implied their differential roles in vitellogenin hydrolysis during oocyte growth and maturation. Many cell cycle-related genes showed the lowest expression at GV0 and then increased expression at GV1 and GV2, which indicated that the resumption of meiosis may be initiated at GV0. The highest expression of the adenyl cyclase genes adcy3a, adcy5, adcy6, adcy6-like, and adcy7 at MV and/or LV, while that of phosphodiesterase genes pde1c, pde4b, pde4b-like, pde4c, pde7a, pde8b, pde10, and of the cyclic AMP-dependent transcription factor atf-3 gene observed at GV0 indicated that cAMP signals may play important roles in oocyte meiotic arrest and resumption in ricefield eels. Parallel expression profiles of urok, mmp2, mmp9, mmp11, mmp14a, mmp14b, mmp17a, mmp19, and mmp25 suggest their potential roles in tissue remodeling during oocyte maturation and ovulation in ricefield eels. Collectively, the data of the present study will aid in further understanding the molecular mechanisms underlying oocyte growth and maturation in ricefield eels as well as in other teleosts.

Fish-specific Toll-like receptor 14 (TLR14) from Asian swamp eel (Monopterus albus) is involved in immune response to bacterial infection

Toll-like receptors (TLRs) are a class of pattern recognition receptors (PRRs) that play a critical role in innate immune responses against pathogens. In the present study, a fish-specific TLR14 was identified and characterized from Monopterus albus (named MaTLR14), which consisted of a 2658 bp open reading frame encoding a protein of 885 amino acids. Phylogenetic analysis revealed that MaTLR14 belong to the TLR1 subfamily and shared the highest similarity to Paralichthys olivaceus TLR14. Immunohistochemistry assay showed that MaTLR14 mainly located in intestinal epithelial cells of hindgut. Immunofluorescence revealed that MaTLR14 largely localized to the intracellular region and partially co-localized with cell membrane of HeLa cells. The expression levels of MaTLR14 were upregulated in the liver, spleen, foregut and hindgut post infection with Aeromonas hydrophila. When stimulated with LPS and Flagellin, the MaTLR14 expression was elevated in isolated peripheral blood leukocytes. Further studies showed that recombinant MaTLR14-LRR could bind to both the gram-negative and gram-positive bacteria and cause agglutination. Subsequently, the signaling pathway of MaTLR14 was investigated. Confocal microscopy and co-immunoprecipitation assay demonstrated that MaTLR14 recruited MyD88 as adaptor. When overexpressed, MaTLR14 augmented the expression of TRAF6 and phosphorylation of ERK and p65, activated NF-κB and AP-1 and elicited the expression of il-6 and tnf-α. Collectively, MaTLR14 plays an important role in the microorganism recognition and signaling transduction.

The therapeutic potential of skin mucus from Asian swamp eel (Monopterus albus): In vivo evaluation and histological evidence

ObjectivesThe Asian swamp eel (Monopterus albus), is commonly distributed in Asian countries. However, its therapeutic potential has not been thoroughly investigated yet. The current study aimed to evaluate the in-vivo therapeutic properties of the skin mucus of this fish. MethodsThe eel mucus was collected fleshly and topical gel with carbopol 934 was formulated to study the antibacterial activity on the infected skin of the rats. Sprague Dawley rats were used in the study and divided into 4 groups negative, positive, normal control, and treated groups. ResultsIntracutaneous injections of pathogenic bacteria (Streptococcus pyogenes, Staphylococcus aureus) and fungi (Microsporum gypseum, Candida albicans) were injected into the rats. The development of tinea capitis, impetigo, and cutaneous candidiasis in the animal model was confirmed based on clinical and histopathological observations. To treat the infected rats, a formulated gel of eel skin mucus was applied on the infected rat’s skins topically. The histological analysis confirms a complete recovery in the skin tissues similar to commercial antifungal and antibacterial agents used in the positive control groups. ConclusionThe present novel eel skin mucus is an efficient therapeutic candidate in treating skin infections associated with pathogenic microbes.

Complete Depletion of Primordial Germ Cells Results in Masculinization of Monopterus albus, a Protogynous Hermaphroditic Fish.

Primordial germ cells (PGCs) play an important role in sexual fate determination and gonadal development in gonochoristic fish, such as zebrafish and medaka. However, little is known about the function of PGCs in hermaphroditic fish. Rice field eel (Monopterus albus), a protogynous hermaphroditic fish, is an economically valuable aquaculture species. We eliminated PGCs in rice field eels during embryogenesis via morpholino-mediated knockdown dead end (dnd). The PGCs-depleted gonads developed into testis-like structures with Sertoli cells and Leydig cells. The gene expression pattern of 15-month-old PGCs-depleted gonads showed that male-biased genes, dmrt1, sox9a, gsdf, and amh, were significantly higher than that of the WT, whereas female-biased genes, foxl2 and cyp19a1a, were significantly decreased. These results indicate that PGCs are essential for ovarian differentiation in rice field eel, and PGCs-depleted gonads develop into sterile males without undergoing the female and intersex stages. Our study is the first to identify the role of PGCs in sex differentiation in rice field eel, a protogynous hermaphrodite teleost. And it is of great significance in rice field eel for discovering the underlying mechanism of sex differentiation and establishing sex control technology.

Taurine supplements in high-carbohydrate diets increase growth performance of Monopterus albus by improving carbohydrate and lipid metabolism, reducing liver damage, and regulating intestinal microbiota

An 8-week feeding trial was performed to investigate the effects of the addition of taurine to high-carbohydrate diets on growth performance, carbohydrate metabolism, lipid deposition, antioxidant ability, inflammation, and intestinal microbiota in juvenile Monopterus albus. Four diets were designed: a control diet (0% corn starch, CON), high-carbohydrate (40% corn starch, HC), and high-carbohydrate diets supplemented with 0.2 and 0.5% taurine (HCT0.2 and HCT0.5, respectively). Each treatment group had 3 replicates. The results showed that the HC feeding significantly decreased growth performance and gluconeogenesis, increased lipid deposition, glycolysis and liver inflammation, and disrupted the intestinal microbiota compared with the CON group. However, compared with the HC group, the addition of taurine to HC diets significantly increased growth performance and the activities of glycolysis and antioxidative enzymes, whereas the opposite occurred in the levels of triglyceride, low-density lipoprotein cholesterol, total cholesterol, and gluconeogenesis enzymes. Additionally, the addition of taurine to HC diets remarkably increased the mRNA expression levels of glycolysis, lipolysis, anti-inflammatory cytokine compared with the HC group, whereas the opposite occurred in the mRNA expression levels of antioxidative enzymes, gluconeogenesis, lipid accumulation, and pro-inflammatory cytokine genes. Besides, the relative abundance of Lactococcus in the HC group remarkably higher than those in the CON group, whereas the opposite occurred in the relative abundance of Clostridium sensu stricto 1. Compared with the CON group, 0.5% taurine supplementation in HC diets showed no significant different on the composition and diversity of intestinal microbiota. Based on the findings, HC diets induced negative effects on rice field eel, and dietary taurine supplementation can improve the growth performance, decrease lipid deposition, enhance antioxidant ability, reduce liver damage, and regulate the homeostasis of intestinal microbiota. And the optimum supplemental level of taurine was 0.5%.

Epidemiological characterization of Clonorchis sinensis infection in humans and freshwater fish in Guangxi, China

BackgroundClonorchiasis is a widespread yet neglected foodborne disease with over 85% of all cases found in China. Guangxi province, located in southeastern China, ranks among the highest endemic provinces. We explore the epidemiological status and determinants of Clonorchis sinensis (C. sinensis) infection in humans and freshwater fish in Guangxi, China.MethodsData on C. sinensis infection in humans from January 2008 to December 2017were extracted from the China Information System for Disease Control and Prevention. An active surveillance of C. sinensis infection in fish was conducted in 2016–2017. County level data including potential environmental, social-economical and behavioral determinants was also collected. Univariate and multivariate logistic regression models were used to explore the determinants of C. sinensis infection in humans and fish. Simple and multiple zero-inflated Poisson regression models were fit to assess the associated factors of clonorchiasis in humans at the county level.ResultsTotally, 4526 C. sinensis cases were reported between 2008 and 2017, with an annual prevalencerate of 0.96/100,000 persons. Of 101 counties in Guangxi, 97 reported at least 1 case. Among 2,098 fish samples, 203 (9.7%) from 70 counties contained C. sinensis. The rate was higher in small fish including Pseudorasbora parva (45.3%), Misgurnus anguillicaudatus (41.2%), Hemicculter leuciclus (34.5%), unclassified small fishes (30.9%), Cyprinidae (20.0%), Cirrhinus molitorella (16.4%), Carassius auratus (13.6%) and Cyprinus carpio (13.3%), while it was lower in fish species that are usually used in preparing raw fish dishes including Ctenopharyngodon idellus (3.6%), Spinibarbus denticulatus (3.7%), Monopterus albus (6.4%), Cyprinus carpio (4.4%), Oreochromis mossambicus (3.3%) and Spualiobarbus Curriculus (6.6%). The C. sinensis infection in fish was only associated with fish species. The estimated human clonorchiasis prevalence at the county level was positively associated with raw fish consumption habits and certain rivers.ConclusionsClonorchiasis is highly prevalent in both humans and freshwater fish in Guangxi. Environmental, social-economic and behavioral determinants contribute to the high prevalence as well as the significant differential distribution by county. Regular surveillance should be implemented for clonorchiasis to demonstrate the change in epidemiology and burden, which will benefit the design of interventions.

An fgf21-like gene from swamp eel (Monopterus albus): Recombinant expression and its potential roles in glucose and lipid homeostasis

Fibroblast growth factor 21 (FGF21) plays important roles in the regulation of glucose and lipid metabolism and energy balance in mammals. In this study, the full-length cDNA of swamp eel fgf21 was cloned. Sequence analysis showed that swamp eel FGF21 displayed high similarity with FGF21 of other vertebrates. Subsequently, a prokaryotic expression vector for swamp eel fgf21 was constructed, and recombinant FGF21 (rFGF21) was successfully induced and purified. To investigate the potential roles of swamp eel FGF21 in glucose and lipid metabolism, we examined the effects of rFGF21 on regulation of glucose and lipid homeostasis in type 1 diabetes mellitus (T1DM) mice as well as swamp eels under glucose stress. In T1DM mice, the levels of blood glucose, serum triglyceride (TG), liver TG, serum total cholesterol (TC), and liver TC were significantly downregulated after repeated daily injection of rFGF21 for 15 days. In addition, liver pathological section analysis indicated that rFGF21 alleviated the degree of damage to liver cells in T1DM mice. Furthermore, rFGF21 significantly upregulated the mRNA expression levels of peroxisome proliferators-activated receptor alpha (Pparα), β-Klotho, fibroblast growth factor receptor 1 (Fgfr1), phosphoenolpyruvate carboxykinase (Pepck), glucose transporter 1 (Glut1), and glucose transporter 4 (Glut4) in T1DM mouse livers. Moreover, in swamp eels, rFGF21 significantly decreased blood glucose and liver TC levels under glucose stress and upregulated the mRNA expression levels of fgf21, pparα, β-klotho, and fgfr1 in liver tissue. These results suggested that FGF21 plays important roles in the regulation of glucose and lipid homeostasis in swamp eel.

Methionine-Mediated Regulation of Intestinal Structure and Lipid Transport in the Rice Field Eel (Monopterus albus)

An eight-week feeding trial discusses how methionine affects intestinal barrier and lipid transport on rice field eel (Monopterus albus). Six isoenergetic and isonitrogenous feeds contained different levels of methionine (0, 2 g/kg, 4 g/kg, 6 g/kg, 8 g/kg, or 10 g/kg). Compared with M0 (0 g/kg), gastric amylase, lipase, and trypsin were remarkably increased as dietary methionine ( P < 0.05 ); intestinal amylase, lipase, and trypsin were remarkably increased in M8 (8 g/kg) ( P < 0.05 ). Compared with M0, gastric fovea was remarkably increased ( P < 0.001 ), gastric epithelium is neater in M8 than that in M0, intestinal villus height and muscular thickness are remarkably increased in M8 ( P < 0.001 ), and amounts of goblet cells per root in M8 were increased ( P > 0.05 ), while intestinal crypt depth was markedly decreased ( P < 0.001 ). Lipid droplets in the intestinal villus and mucosal layer in the M8 (8 g/kg) group were more than that in M0 (0 g/kg). Compared with M0 (0 g/kg), the intestinal gcn2 and eif2α were downregulated in M8 (8 g/kg) ( P < 0.01 and P < 0.05 , respectively), while occ, cl12, cl15, zo-1, zo-2, hdlbp, ldlrap, npc1l1, cd36, fatp1, fatp2, fatp6, apo, apoa, apob, apoc, apoe, mct1, mct2, mct8, lpl, mttp, moat2, and dgat2 were upregulated markedly in M8 (8 g/kg). Intestinal eif2α expression was positively correlated with gcn2, and intestinal zo-1, cl15, fatp6, ldlrap, mct2, mct8, apo, apob, mct1, apoc, fatp1, mttp, cd36, occ, npc1l1, hdlbp, fatp2, apoe, lpl, and moat2 gene expression was negatively correlated with gcn2. In conclusion, methionine deficiency affected the gastric and intestinal structures, damaged the intestinal barrier, and decreased lipid and fatty acid transport. Besides, gcn2 could be activated when M. albus was fed methionine-deficient feed.

Identification and expression analysis of thyroid-stimulating hormone β subunit, and effects of T3 on gonadal differentiation-related gene expression in rice field eel, Monopterus albus.

Thyroid-stimulating hormone (TSH) is an important glycoprotein in hypothalamic-pituitary-thyroid axis, which plays a crucial role in the synthesis and release of thyroid hormones in vertebrates. Rice field eel, Monopterus albus, a protogynous hermaphroditic fish, which undergoes sex reversal from a functional female to a male, is an ideal model to investigate the regulation of sex differentiation. In this study, we obtained the cDNA sequence of thyroid-stimulating hormone β subunit (tshβ) from rice field eel, which contained a complete open reading frame and encoded a putative protein of 151 amino acids. Multiple alignment of protein sequences showed that tshβ was highly conserved in teleost. The tissue distribution indicated that tshβ showed high expression in the pituitary, moderate expression in the brain region, gonad, intestine and liver, and low expression in other peripheral tissues. During natural sex reversal, the expression of tshβ had no significant difference in the pituitary. Compared to that in the ovary, the expression of tshβ increased significantly in the gonad at late intersexual and male stages. After treatment by different doses of triiodothyronine (T3) (1μg/g, 10μg/g and 100μg/g body weight), serum T3 and free triiodothyronine (FT3) increased sharply, while the expression of tshβ were inhibited significantly in the pituitary. Although T3 had no significant effect on the levels of serum E2, it stimulated the release of serum 11-KT at high-dose group. We also detected the effects of T3 on the expression of gonadal differentiation-related genes in rice field eel. T3 treatment inhibited the expression of foxl2, cyp19a1a and dax1, while stimulated the expression of sox9a1. These results indicate that TSH may be involved in sex differentiation, and THs may play roles in the regulation of male development and sex reversal in rice field eel.

Aromatase inhibitor induces sex reversal in the protogynous hermaphroditic rice field eel (Monopterus albus)

The rice field eel (Monopterus albus) is a protogynous hermaphroditic fish reared commercially as an aquaculture species in East Asia. Artificial breeding of rice field eels requires an abundance of adult females and males; however, the eels need to undergo a long period of female and intersexual stages before they develop into males, which results in a shortage of functional males in production practice. This study developed an artificial method for producing functional males through the oral administration of an aromatase inhibitor (AI, letrozole: 300 mg/kg feed) in juvenile fish. Histological analysis of gonadal sections of treated fish revealed the transition of primary ovaries to mature testes. During the initial period of the AI treatment, 2-month-old rice field eels were exclusively female. AI administration resulted in a significant reduction in 17β-estradiol levels and increase in testosterone and 11-ketotestosterone levels in vivo. Cell proliferation occurred in the outer layer of the gonadal epithelium, and oocytes degenerated in the ovaries. After 120 days of AI treatment, the ovaries were completely converted to testes. The sexually reversed fish maintained the male sex and produced functional sperm after cessation of drug treatment. Notably, artificially sex-reversed males' fecundity did not differ significantly from wild-type males. Quantitative PCR analysis revealed that the expression of cyp19a1a decreased, whereas the mRNA levels of estrogen receptors esr1, esr2a, and esr2b increased significantly during AI treatment. Moreover, the expression of foxl2 was downregulated, whereas dmrt1, amh, and sox9 were upregulated in the gonads of fish administered AI. This study revealed that endogenous estrogen synthesis plays a key role in the sex change of rice field eels, with ovaries undergoing a reversal to testes in response to estrogen insufficiency. Such artificially induced sex conversion will be of considerable value in breeding rice field eels.

Physicochemical Properties and Nutrient Content of Tempe Flour Enriched Eel Flour

AIM: This study aims to evaluate the nutritional content and physicochemical aspect of the combination of eel and tempe flour. METHODS: Samples of swamp eel and tempe flour were combined in a ratio of 1:1 (A), 1:2 (B), 1:3.5 (C), and 1 kilogram of Asian swamp eel meat without additional tempe (D), respectively. Homogenization was done using a sinmag planetary mixer. The sample analysis was performed at the SIG Laboratory (PT. Saraswanti Indo Genetech) on November 16, 2021. The samples were analyzed triple (triplicates). Statistical analysis was performed using GraphPad Prism version 9.3.0 for Mac OS. Variables were analyzed using multivariate ANOVA with 95% CI (0.05). RESULTS: There was a significant difference between Samples A, B, C, and D for every proximate analysis parameter (p = 0.000) p < 0.05. The results showed a significant difference in the unsaturated fatty acid parameter between the groups (p < 0.001). Sample C has the highest B9 (folic acid) content compared to other samples (1258.53 ± 1.39 mcg/100 g) and a significant difference was found between samples (p < 0.0001). CONCLUSION: Tempe flour enriched eel flour can act as a source of folate, due to its high folate content. Tempe flour enriched eel flour could be used as a flour mixture in any food products that require flour to increase folate content.

Crosstalk between sex-related genes and apoptosis signaling reveals molecular insights into sex change in a protogynous hermaphroditic teleost fish, ricefield eel Monopterus albus

The ricefield eel Monopterus albus is a protogynous hermaphroditic synbranchiform species that undergoes sequential sex change from female to male, offering an interesting model for study in the mechanisms of sequential hermaphroditism in vertebrates. To explore the expression patterns and molecular mechanisms of key genes underlying sex change in the ricefield eel M. albus, a comprehensive study of the transcriptomes of gonads at five sexual stages (ovary, early intersexual stage gonad, middle intersexual stage gonad, late intersexual stage gonad, and testis) was performed. In total, 107,260,808 raw reads and 101,886,556 clean reads were obtained, and 41,216 genes were detected in the gonad tissues. The expression levels of 21 differentially expressed genes were verified by quantitative real-time PCR (qRT-PCR) and found to be in accordance with the RNA-seq data, suggesting that the RNA-seq data were reliable. Furthermore, the expression of female-related genes decreased as sex change progressed, whereas male-related genes exhibited the opposite expression patterns. Notably, apoptosis-related genes had close relationships with sex change, including genes associated with endocytosis, calcium signaling pathways, and 7 other pathways. In particular, apoptosis signaling was delivered to the p53 network, which may be associated with sex change. Importantly, tgfb3, fshr, camk4 and calmodulin may be the key genes, which helps balance germ cell apoptosis and proliferation during sex change. These results reveal specific molecular signatures in the gonad that are related to sex change and apoptosis signaling, which will be useful for enhancing our understanding of sequential hermaphroditism and sex change in the ricefield eel M. albus and other teleost.

Intervention of taurine on fatty acid profiles, oxidative injury and autophagy status in the muscle of rice field eel (Monopterus albus) fed oxidized fish oil

Fish oil is the primary oil source in the aquatic feed, easily oxidized in feed production and storage. To avoid the potentially negative effects caused by oil oxidation and diversify the study of taurine in aquatic animals, the present study was carried out to investigate the effects of taurine on fatty acid composition, oxidative stress and autophagy status in the muscle of rice field eel (Monopterus albus) subjected to oxidized fish oil (OFO) feed. The feeding experiment was conducted for 8 weeks, and three isonitrogenous and isolipidemic experimental diets were set, namely CON (containing 2% fresh fish oil), OFO (containing 2% OFO), OFOT (containing 2% OFO and 0.2% taurine). A total of 450 eels with an initial weight of 30.06 ± 0.03 g were chosen and randomly distributed to 9 tanks for feeding. It could be found that the muscle moisture and crude protein contents significantly increased in the OFO group (P < 0.05). Dietary taurine significantly increased the muscle n3 PUFA content compared to the OFO group (P < 0.05), and the significantly increased n6 PUFA and total fatty acid contents could be observed in the OFO and OFOT group (P < 0.05). Moreover, dietary taurine significantly decreased myofiber density and muscle hardness by up-regulating the expression of MRF4, Myf5 and MyoD1 compared to the OFO group (P < 0.05), with a larger myofiber diameter due to the decreased connective tissue ratio. Furthermore, dietary taurine alleviated the disturbance of muscle redox endocytosis associated with oxidized fish oil by up-regulating Nrf2 to activate antioxidant enzymes and clear reactive oxygen species (ROS) and malondialdehyde (MDA) in the muscle. Autophagy levels induced by oxidized fish oil improved in the OFOT group, as evidenced by a decrease in protein expression of microtubule-associated protein 1 light chain 3 (LC3). In summary, muscle nutritional composition, redox status and autophagy levels were potentially cross-linked to muscle quality. Dietary taurine reshaped muscle fatty acid composition and effectively improved the extent of muscle oxidative stress and autophagy status induced by oxidized fish oil, leading to greater muscle quality.

IKAN AIR TAWAR DI SUNGAI BATANG MUAR DESA SERAMI KABUPATEN MUKOMUKO

This study aimed to look at the inventory of freshwater fish species in the Batang Muar River, Serami Baru Village, Mukomuko Regency, Bengkulu. This study uses an exploratory descriptive research method by using a survey technique conducted by determining the point of observation. Determination of the location of the research is done by the method of purposive sampling. The samples obtained were grouped based on the same morphological characteristics and the number of each type was counted. Based on the results of the research, the results of the inventory of freshwater fish species in the Batang Muar River found 9 species consist of Oxyeleotris marmota, Angulia marmorata, Monopterus albus, Tor putitora, Labiobarbus leptocheilus, Mystacoleucus padanggensis, Osteochiolus vittatus, Chana striata and Schismatgobius ridawatiae.

Fish Diversity Monitored by Environmental DNA in the Yangtze River Mainstream

Surveys and assessments based on environmental DNA are not only efficient and time-saving, but also cause less harm to monitoring targets. Environmental DNA has become a common tool for the assessment and monitoring of aquatic organisms. In this study, we investigated fish resources in the Yangtze River mainstream using environmental DNA, and the variations in fish during two seasons (spring and autumn) were compared. The results showed that 13 species were identified in spring, and nine species of fish were identified in autumn. The fish with higher eDNA detection were Sinibotia superciliaris, Tachysurus fulvidraco, Cyprinus carpio, Ctenopharyngodon Idella, Monopterus albus, Acanthogobius hasta, Saurogobio dabryi, Oncorhynchus mykiss, Mugil cephalus, Odontamblyopus rubicundus. Seasonal variation between spring and autumn was not significant, and the environmental factors had different effects on fish assemblages during the two seasons. Our study used the eDNA technique to monitor the composition of fish in the spring and autumn in the Yangtze River mainstream, providing a new technology for the long-term management and protection of fishery resources in the region. Of course, problems such as pollution and insufficient databases are the current shortcomings of environmental DNA, which will be the focus of our future research and study.

A Study on How Methionine Restriction Decreases the Body's Hepatic and Lipid Deposition in Rice Field Eel (Monopterus albus).

Methionine restriction reduces animal lipid deposition. However, the molecular mechanism underlying how the body reacts to the condition and regulates lipid metabolism remains unknown. In this study, a feeding trial was performed on rice field eel Monopterus albus with six isonitrogenous and isoenergetic feeds that included different levels of methionine (0, 2, 4, 6, 8, and 10 g/kg). Compared with M0 (0 g/kg), the crude lipid and crude protein of M. albus increased markedly in M8 (8 g/kg) (p < 0.05), serum (total cholesterol, triglyceride, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and non-esterified free fatty acids), and hepatic contents (hepatic lipase, apolipoprotein-A, fatty acid synthetase, total cholesterol, triglyceride, and lipoprteinlipase). However, in the serum, very-low-density lipoprotein and hepatic contents (hormone-sensitive triglyceride lipase, Acetyl CoA carboxylase, carnitine palmitoyltransterase, and mirosomal triglygeride transfer protein) decreased markedly in M8 (p < 0.05). The contents of hepatic C18:2n-6, C22:6n-3, and n-3PUFA in the M8 group were significantly higher than those in M0 (p < 0.05), and the contents of lipid droplets in M8 were higher than those in M0. Compared with M0, the hepatic gcn2, eif2α, hsl, mttp, ldlrap, pparα, cpt1, and cpt2 were remarkably downregulated in M8, while srebf2, lpl, moat2, dgat2, hdlbp, srebf1, fas, fads2, me1, pfae, and icdh were markedly upregulated in M8. Moreover, hepatic SREBP1 and FAS protein expression were upregulated significantly in M8 (p < 0.01). In short, methionine restriction decreased the lipid deposition of M. albus, especially for hepatic lipid deposition, and mainly downregulated hepatic fatty acid metabolism. Besides, gcn2 could be activated under methionine restriction.