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Monopterus albus is one of the popular aquatic fish in Asia. Manual processing of eel cannot fully meet the large- scale production at present, due to the time-consuming, laborious, and low safety. In view of its slender and slimy body, an eel- cutting machine is required for the consumption of Monopterus albus. In this study, a miniature machine of automatic cutting was designed for the living Monopterus albus with a sticky surface. The machine consisted of conveying, clamping, and cutting parts. The double-clamped wheel to roller was used to capture the eel for transportation during cutting. The switch between laparotomy and back dissection was realized to change the feeding channel. The adaptive mechanism was equipped to meet the requirements of different sizes of eel cutting. Firstly, the geometry and weight parameters of Monopterus albus were measured using a straight ruler and precision electronic balance. The tribological parameters on the surface of Monopterus albus were measured by the inclined plane. The mechanical parameters of Monopterus albus meat were verified by compression test. Secondly, according to the rigid-flexible coupling principle, the rigid-damping model was equivalent to the contact between the Monopterus albus body and the clamping wheel and slide. The rigid-flexible coupling model was established by Abaqus and Adams simulation software. The analysis model was optimized to take the conveying time of the fish body, output speed, clamping force, and whole machine vibration as the test indexes in single-factor tests, such as the spring stiffness, slope Angle of the slide, and the speed of the clamping wheel. The results show that the clamping force first increased and then decreased with the increase of spring stiffness and the vibration amplitude of the whole machine decreased. But there was little influence on conveying time and output speed. The output time of the fish body decreased with the increase of slope angle, while the output speed, clamping force, and vibration of the whole machine increased. There was an increase in the conveying time of the fish body, the output speed, the clamping force, and the vibration of the whole machine, with the increase of the speed of the clamping wheel. The single- and multi-factor analyses were carried out to obtain the optimal working conditions. Specifically, the clamping wheel speed was 600 r/min, the spring stiffness was 1 200 N/m, and the slope angle was 16°. Finally, the processing experiment was performed on the automatic cutting machine for eel. There was consistency in the vibration amplitude range and the relationship between the three directions of the machine measuring points with the theoretical analysis. At the same time, the output speed of the fish body output machine was also measured to better agree with the theoretical analysis. The cutting of the machine under optimal working conditions has fully met the requirements. The correctness of the theoretical analysis was also verified by the test. The rigid-flexible coupling model can provide a strong reference to research and develop the subsequent equipment. [ABSTRACT FROM AUTHOR]

The scale of Monopterus albus farming in Hubei Province is large, but there are few pre-treatment processing devices. The current Monopterus albus pretreatment device is mainly dissected and killed. Aiming at the problems of poor stability, low efficiency, and low meat yield of existing Monopterus albus deboning devices, an adaptive Monopterus albus deboning device was designed, which was mainly composed of laparotomy components, transitional components, and deboning components. The theoretical analysis of the process of fish laparotomy, transition transportation, and deboning was carried out, and the key factors affecting the performance of the deboning device were obtained. Taking the meat yield rate and sensory quality scores as evaluation indexes, the single-factor test of the distance between the pressure wheel and the V-block, the initial clearance of the transition wheel, the rotational speed of the transition wheel, the shape of the deboning blade disc and the rotational speed of deboning blade disc were carried out to determine the reasonable range of each parameter. The test results showed that when the distance between the pressure wheel and the V-block was 15.50-16.75 mm, the meat yield rate was higher; when the initial clearance of the transition wheel was 9 mm, the sensory quality scores of the fish body was the highest; the increase of the rotational speed of the transition wheel and the rotational speed of the deboning blade disc is beneficial to improve the meat yield rate and sensory quality scores; and the shape of the boning blade disc had little influence on the meat yield rate and the sensory quality scores. The orthogonal test of four factors and three levels was carried out with the distance between the pressure wheel and the V-block, the initial clearance of the transition wheel, the rotational speed of the transition wheel, and the rotational speed of the deboning blade disc as the test factors. The results showed that the order of significance of each test factor on the meat yield rate was the distance between the pressure wheel and the V-block, the initial clearance of the transition wheel, the rotational speed of the transition wheel, and the rotational speed of the deboning blade disc; and the order of significance on the sensory quality scores was the initial clearance of the transition wheel, the distance between the pressure wheel and the V-block, the rotational speed of the transition wheel and the rotational speed of the deboning blade disc. When the distance between the pressure wheel and the V-block was 16.75 mm, the initial clearance of the transition wheel was 9 mm, the rotational speed of the transition wheel was 648 r/min, and the rotational speed of the deboning blade disc was3200 r/min, the deboning effect was the best. The meat yield rate of the deboning device was 84%, and the total sensory quality scores of the fish after processing reached 17.3. The device can process Monopterus albus with a body mass of 75-150 g, and the production efficiency reaches 16.8 strips/min. Compared with the current commercially available deboning device, the feeding is more convenient and the production efficiency is higher. It can provide a reference for the research of Monopterus albus pretreatment device. [ABSTRACT FROM AUTHOR]

• LNF exhibited a high freezing rate and contributed to small ice crystal forming. • LNF maintained WHC and shear force of Monopterus albus. • LNF alleviated myofibrillar protein denaturation of Monopterus albus. • LNF at −110 °C is more suitable for Monopterus albus than LNF at −50 °C and −80 °C. Monopterus albus is highly susceptible to spoilage due to high protein and moisture contents while frozen storage can effectively prolong the shelf-life. To study the effect of liquid nitrogen freezing (LNF) on quality, microstructure of ice crystal and muscle fiber, and physicochemical properties of proteins, Monopterus albus was frozen at -20 °C by refrigerator (RF, control), -50 °C, -80 °C, and -110 °C by LNF, respectively. The -110 °C LNF exhibited the highest freezing rate among four groups, contributing to the formation of small ice crystals with more uniform distribution and alleviating the damage to muscle fiber. In -110 °C LNF group, protein secondary structure changed relatively subtle, resulting in high protein solubility, Ca2+-ATPase activity, and total sulfhydryl content, as well as low surface hydrophobicity and disulfide bond content. LNF retarded the rise of TVB-N value, prevented the loss of immobilized and free water, and maintained water holding capacity and shear force. In conclusion, -110 °C LNF was recommended a promising freezing process for frozen Monopterus albus due to less alteration of quality and alleviation of protein denaturation. [Display omitted] [ABSTRACT FROM AUTHOR]

The aim of this experiment was to study the effects of stickwater hydrolysate meal on growth, intestinal digestive enzymes, serum biochemistry and immune indexes of rice field eel (Monopterus albus). Healthy rice field eel with an initial weight of (25.00±0.20) g were used as the study subjects, and three treatment groups were set up with three replicates in each group and 50 rice field eel per box. Stickwater hydrolysate meal was used to replace 0, 2.5% and 5% fishmeal in the basal diet (fishmeal content of 40%), recorded as FM, SHM2.5 and SHM5.0, respectively, and the breeding experiment lasted 56 days. The results showed that the replacement of some fish meal (SHM2.5 and SHM5.0) by stickwater hydrolysate meal did not have any significant difference on the weight gain rate (WGR) of rice field eel (P>0.05); but significantly increased the intestinal trypsin (TPS) activity (P<0.05); the replacement of some fish meal by stickwater hydrolysate meal had no significant effect on the serum total cholesterol (TC), urea nitrogen (BUN), total bile acids (TBA), glutamic-pyruvic transaminase (GPT), glutamic oxaloacetic transaminase (GOT), complement 3 (C3), malondialdehyde (MDA), alkaline phosphatase (AKP) and superoxide dismutase (SOD) of rice field eel. There were no significant differences in the levels of alkaline phosphatase, malondialdehyde and superoxide dismutase (P>0.05); the replacement of some fish meal by stickwater hydrolysate meal significantly increased the levels of serum immunoglobulin M (IGM), complement 4 (C4) and lysozyme (LZM) (P<0.05), and the levels of serum glucose (GLU), triglyceride (TG) and alkaline phosphatase in the SHM5.0 group were significantly elevated (P<0.05). The results indicated that proper replacement of fish meal by stickwater hydrolysate meal has no adverse effect on growth, feed utilization and intestinal digestive enzymes of rice field eel and will enhance the immune function of rice field eel. [ABSTRACT FROM AUTHOR]

Abstract Background Cyp19a1a is a key enzyme in the pathway that converts androgens into estrogen and is regulated by TGF-β signaling. Smad4 and FoxH1 are downstream effectors of TGF-β signaling and may play important roles in ovarian development in M. albus. Methods We investigated the expression pattern of the Smad4 and FoxH1 using qRT‒PCR and immunofluorescence, then tested the changes of smad4 and foxh1 by qRT‒PCR after ovary incubation with FSH in vitro, and analysed the regulation of cyp19a1a transcription by Smad4 and FoxH1 by dual-luciferase reporter assays. Results We found that Smad4 encoded a putative protein of 449 amino acids and harbored the three conserved domains typical of this protein family. Smad4 and foxh1 exhibited similar expression patterns during ovarian development and after FSH incubation, with Pearson’s coefficients of 0.873 and 0.63–0.81, respectively. Furthermore, Smad4, FoxH1 and Cyp19a1a colocalized in the granulosa cells and theca cells of ovaries during the mid-to-late vitellogenic stage. Smad4 repressed cyp19a1a activity via SBE1 (− 1372/−1364) and SBE2 (− 415/−407) in the cyp19a1a promoter, whereas mutating SBE1 or SBE2 restored cyp19a1a promoter activity. Co-overexpression of Smad4 and FoxH1 significantly reduced cyp19a1a promoter activity. Conclusions This study provides new insights into the potential functions of transcription factors Smad4 and FoxH1 in ovarian development and the transcriptional regulation mechanism of cyp19a1a in M. albus, which will reveal Smad4/FoxH1-mediated TGF-β signaling in reproduction and the regulation of the cyp19a1a. Plain English summary Aromatase, encoded by cyp19a1a, is involved in ovarian development and plays an important role in the quality of eggs, as well the sex ratio, of the teleost fish, M. albus. The research on the transcriptional regulation of cyp19a1a has contributed to the understanding of its role in ovarian development. In previous study, it was shown that FoxH1 inhibits cyp19a1a transcription. In the present study, Smad4 was confirmed as a cyp19a1a transcriptional repressor and Smad4 may also coordinate with FoxH1 to repress cyp19a1a transcription. At present, we provide a new perspective for the transcriptional regulation of cyp19a1a by transcription factors Smad4 and FoxH1 in teleost fish ovary. In the future, the regulatory networks of Smad4 and FoxH1 will be further studied and the gene editing technology will be applied to screen specific regulatory factors of cyp191a1a gene, so as to alter the female cycle and modulate the sex ratio of the eggs production.

Abstract Background The ricefield eel Monopterus albus undergoes a natural sex change from female to male during its life cycle, and previous studies have shown the potential mechanisms of this transition at the transcriptional and protein levels. However, the changes in protein levels have not been fully explored, especially in the intersexual stage. Results In the present study, the protein expression patterns in the gonadal tissues from five different periods, the ovary (OV), early intersexual stage gonad (IE), middle intersexual stage gonad (IM), late intersexual stage gonad (IL), and testis (TE), were determined by untargeted proteomics sequencing. A total of 5125 proteins and 394 differentially expressed proteins (DEPs) were detected in the gonadal tissues. Of the 394 DEPs, there were 136 between the OV and IE groups, 20 between the IM and IE groups, 179 between the IL and IM groups, and 59 between the TE and IL groups. Three candidate proteins, insulin-like growth factor 2 mRNA-binding protein 3 isoform X1 (Igf2bp3), triosephosphate isomerase (Tpi), and Cu-Zn superoxide dismutase isoform X1 [(Cu-Zn) Sod1], were validated by western blotting to verify the reliability of the data. Furthermore, metal metabolite-related proteins were enriched in the IL vs. IM groups and TE vs. IL groups, which had close relationships with sex change, including Cu2+-, Ca2+-, Zn2+- and Fe2+/Fe3+-related proteins. Analysis of the combined transcriptome data revealed consistent protein/mRNA expression trends for two metal metabolite-related proteins/genes [LOC109953912 and calcium Binding Protein 39 Like (cab39l)]. Notably, we detected significantly higher levels of Cu2+ during the sex change process, suggesting that Cu2+ is a male-related metal metabolite that may have an important function in male reproductive development. Conclusions In summary, we analyzed the protein profiles of ricefield eel gonadal tissues in five sexual stages (OV, IE, IM, IL, and TE) and verified the plausibility of the data. After preforming the functional enrichment of metal metabolite-related DEPs, we detected the contents of the metal metabolites Zn2+, Cu2+, Ca2+, and Fe2+/Fe3+ at these five stages and screened for (Cu-Zn) Sod1 and Mmp-9 as possible key proteins in the sex reversal process.

Background: Cyp19a1a is a key enzyme in the pathway that converts androgens into estrogen and is regulated by TGF-β signaling. Smad4 and FoxH1 are downstream effectors of TGF-β signaling and may play important roles in ovarian development in M. albus. Methods: We investigated the expression pattern of the Smad4 and FoxH1 using qRT‒PCR and immunofluorescence, then tested the changes of smad4 and foxh1 by qRT‒PCR after ovary incubation with FSH in vitro, and analysed the regulation of cyp19a1a transcription by Smad4 and FoxH1 by dual-luciferase reporter assays. Results: We found that Smad4 encoded a putative protein of 449 amino acids and harbored the three conserved domains typical of this protein family. Smad4 and foxh1 exhibited similar expression patterns during ovarian development and after FSH incubation, with Pearson's coefficients of 0.873 and 0.63–0.81, respectively. Furthermore, Smad4, FoxH1 and Cyp19a1a colocalized in the granulosa cells and theca cells of ovaries during the mid-to-late vitellogenic stage. Smad4 repressed cyp19a1a activity via SBE1 (− 1372/−1364) and SBE2 (− 415/−407) in the cyp19a1a promoter, whereas mutating SBE1 or SBE2 restored cyp19a1a promoter activity. Co-overexpression of Smad4 and FoxH1 significantly reduced cyp19a1a promoter activity. Conclusions: This study provides new insights into the potential functions of transcription factors Smad4 and FoxH1 in ovarian development and the transcriptional regulation mechanism of cyp19a1a in M. albus, which will reveal Smad4/FoxH1-mediated TGF-β signaling in reproduction and the regulation of the cyp19a1a. Plain English summary: Aromatase, encoded by cyp19a1a, is involved in ovarian development and plays an important role in the quality of eggs, as well the sex ratio, of the teleost fish, M. albus. The research on the transcriptional regulation of cyp19a1a has contributed to the understanding of its role in ovarian development. In previous study, it was shown that FoxH1 inhibits cyp19a1a transcription. In the present study, Smad4 was confirmed as a cyp19a1a transcriptional repressor and Smad4 may also coordinate with FoxH1 to repress cyp19a1a transcription. At present, we provide a new perspective for the transcriptional regulation of cyp19a1a by transcription factors Smad4 and FoxH1 in teleost fish ovary. In the future, the regulatory networks of Smad4 and FoxH1 will be further studied and the gene editing technology will be applied to screen specific regulatory factors of cyp191a1a gene, so as to alter the female cycle and modulate the sex ratio of the eggs production. Highlights: Smad4 and foxh1 were closely correlated with ovarian development, and Pearson's coefficient was 0.873. FSH incubation stimulated the expression of smad4 and foxh1 in the ovaries. Smad4, FoxH1 and Cyp19a1a colocalized in the granulosa cells and theca cells of ovaries. Smad4 and FoxH1 potentially synergistically suppress the activity of cyp19a1a promoter. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the impacts of wild and breeding juvenile rice field eel under conditions of ammonia and heat stress. The growth performance (FBW, WGR, SGR, and FCR) of 360 wild (24.22 ± 0.30 g) and 360 breeding (24.16 ± 0.27 g) strains was significantly hindered by ammonia and heat stress. The inhibitory effects were more obvious when the two stresses were combined. The growth performance and survival rates of the breeding strains outperformed that of the wild strains under identical stress conditions, this was explained by the expression of the growth-related gene (gh). They have increased the enzyme activity (CAT and GSH-Px) and expression of immune-related genes (cat, gpx3, and hsp90a) in response to oxidative stress. However, the results of certain indicator enzymes indicate the presence of oxidative damage in their tissues. The presence of an inflammatory response in the tissues was suggested by the up-regulation of genes associated with pro-inflammatory cytokines (il-1b and il-8) and the downregulation of genes related to anti-inflammatory cytokines (il-10). Additionally, the presence of tissue damage was shown by the up-regulation of genes connected to apoptosis (cas2, cas8, and cas9) and the down-regulation of genes connected to tight junctions (zo-1). Nevertheless, it is noteworthy that breeding strains exhibited superior adaptability to ammonia and heat stress in comparison to wild strains. [ABSTRACT FROM AUTHOR]

This document is a compilation of research articles that focus on the gut microbiota of fish. The articles cover a range of topics, including the impact of sampling season and catching site on gut microbiota composition, the effects of diet on the microbiota and health of fish, the role of gut microbiota in fish disease and immunity, and the interactions between the gut microbiome and the aquatic environment in fisheries and aquaculture. These articles provide valuable insights into the diversity and functions of fish gut microbiota and its implications for fish health and aquaculture practices. [Extracted from the 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. [ABSTRACT FROM AUTHOR]

Background: The ricefield eel Monopterus albus undergoes a natural sex change from female to male during its life cycle, and previous studies have shown the potential mechanisms of this transition at the transcriptional and protein levels. However, the changes in protein levels have not been fully explored, especially in the intersexual stage. Results: In the present study, the protein expression patterns in the gonadal tissues from five different periods, the ovary (OV), early intersexual stage gonad (IE), middle intersexual stage gonad (IM), late intersexual stage gonad (IL), and testis (TE), were determined by untargeted proteomics sequencing. A total of 5125 proteins and 394 differentially expressed proteins (DEPs) were detected in the gonadal tissues. Of the 394 DEPs, there were 136 between the OV and IE groups, 20 between the IM and IE groups, 179 between the IL and IM groups, and 59 between the TE and IL groups. Three candidate proteins, insulin-like growth factor 2 mRNA-binding protein 3 isoform X1 (Igf2bp3), triosephosphate isomerase (Tpi), and Cu-Zn superoxide dismutase isoform X1 [(Cu-Zn) Sod1], were validated by western blotting to verify the reliability of the data. Furthermore, metal metabolite-related proteins were enriched in the IL vs. IM groups and TE vs. IL groups, which had close relationships with sex change, including Cu2+-, Ca2+-, Zn2+- and Fe2+/Fe3+-related proteins. Analysis of the combined transcriptome data revealed consistent protein/mRNA expression trends for two metal metabolite-related proteins/genes [LOC109953912 and calcium Binding Protein 39 Like (cab39l)]. Notably, we detected significantly higher levels of Cu2+ during the sex change process, suggesting that Cu2+ is a male-related metal metabolite that may have an important function in male reproductive development. Conclusions: In summary, we analyzed the protein profiles of ricefield eel gonadal tissues in five sexual stages (OV, IE, IM, IL, and TE) and verified the plausibility of the data. After preforming the functional enrichment of metal metabolite-related DEPs, we detected the contents of the metal metabolites Zn2+, Cu2+, Ca2+, and Fe2+/Fe3+ at these five stages and screened for (Cu-Zn) Sod1 and Mmp-9 as possible key proteins in the sex reversal process. [ABSTRACT FROM AUTHOR]

To investigate the impact of the effect of high temperature stimulation on Monopterus albus larvae after a certain period of time, five experimental groups were established at different temperatures. Then, the M. albus under high temperature stress was fed at 30°C for 70 days. After that, the growth index of the M. albus was counted and analyzed. In terms of growth index, high temperature stress had significant effects on FCR, FBW, WGR, and SGR of M. albus (p < 0.05). The SR increased after being stimulated by temperature (p < 0.1). The study revealed that liver cells of M. albus were harmed by elevated temperatures of 36°C and 38°C. In the experimental group, the activities of digestive enzymes changed in the same trend, reaching the highest point in the 32°C group and then decreasing, and the AMS activity in the 38°C group was significantly different from that in the 30°C group (p < 0.05). The activities of antioxidase in liver reached the highest at 34°C, which was significantly different from those at 30°C (p < 0.05). In addition, the expression levels of TLR1, C3, TNF-α, and other genes increased in the experimental group, reaching the highest point at 34°C, and the expression level of the IL-1β gene reached the highest point at 32°C, which was significantly different from that at 30°C (p < 0.05). However, the expression level of the IRAK3 gene decreased in the experimental group and reached its lowest point at 34°C (p < 0.05). The expression level of the HSP90α gene increased with the highest temperature stimulus and reached its highest point at 38°C (p < 0.05). In the α diversity index of intestinal microorganisms in the experimental group, the observed species, Shannon, and Chao1 indexes in the 34°C group were the highest (p < 0.05), and β diversity analysis revealed that the intestinal microbial community in the experimental group was separated after high temperature stimulation. At the phylum level, the three dominant flora are Proteus, Firmicutes, and Bacteroides. Bacteroides and Macrococcus abundance increased at the genus level, but Vibrio and Aeromonas abundance decreased. To sum up, appropriate high-temperature stress can enhance the immunity and adaptability of M. albus. These results show that the high temperature stimulation of 32°C–34°C is beneficial to the industrial culture of M. albus. [ABSTRACT FROM AUTHOR]

Swamp eel (Monopterus albus) is an important freshwater culture fish in China and has the characteristic of hermaphroditism and natural sexual reversal. Currently, there is a lack of artificial varieties within swamp eel cultivation, and the fry of mainly rely on the wild catching. Gynogenesis, a method for rapidly obtaining fish population with stable heredity and excellent character, was explored in this study. Meiogynogenesis induction was established in swamp eel, resulting in the creation of three gynogenic populations characterized by deep-yellow coloration. Flow cytometry analysis showed that the cellular DNA contents of gynogenic eels were consistent with those of wild type fish, and chromosome counting confirmed the diploid nature with 48 chromosomes. Histological analysis demonstrated the development of ovaries in the gonads of gynogenic eels, indicating normal diploid functionality. Microsatellite diversity analysis showed that the effective number of alleles (Ne), Shannon's information index (I), polymorphism information content (PIC), observed heterozygosity (Ho) and expected heterozygosity (He) in gynogenic eels were significantly lower than those in the wild population. The genetic homozygosity in gynogenetic eels exhibited a significant improvement. The genetic distance increased and the genetic similarity decreased between gynogenetic groups. In summary, the gynogenetic population of the deep-yellow swamp eels provides new materials for breeding excellent varieties. [ABSTRACT FROM AUTHOR]

Asian swamp eels (Monopterus albus/javanensis) were first reported as introduced to Florida waterbodies in 1997 near Tampa and Miami; a third population was recorded by 1999 in Homestead. Initial assessments, published soon after swamp eels in southern Florida were first recorded in wetlands beyond canals and ponds (in 2007), concluded there was little threat to Florida’s aquatic ecosystems. Long-term data now suggest they precipitated population crashes of crayfishes and small fishes in the eastern Everglades. We used records from continuous long-term monitoring programs, sporadic monitoring studies, and online databases to reconstruct swamp eel presence across Florida. Monitoring studies provided wetland hydrologic variables to assess limits for swamp eels. From 1997–2007, populations in southern Florida remained restricted to canals; initial spread from 2007–2017 across southern Everglades National Park proceeded slowly and the two populations covered ~1500 km² of southern Florida. From 2017–2022, the rate of spread increased as they spread west and north (~5800 km² range). Through 2014, the Tampa population occurred only along southern/eastern Tampa Bay (~60 km²) but has since spread south along the Gulf Coast, east into central Florida, and south along the Lake Wales Ridge (~11,000 km²). We found evidence of two potentially new introductions, in Palm Beach County and Orlando. There was no clear evidence of limitation of wetland drying on swamp eel occurrence in the Everglades; they were captured in marshes that dried for 1–5 months during the previous dry season, but short-hydroperiod wetlands may have slowed spread. In the Everglades, evidence suggests swamp eels may have been inadvertently spread into marshes from canals used to deliver water for flood control and hydrologic restoration. Swamp eels are currently spreading unchecked across Florida, and there should be great concern about continued spread in this region and their establishment and spread elsewhere. [ABSTRACT FROM AUTHOR]

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In order to solve the problems of the low feeding rate, incomplete digestion of Monopterus albus, and nitrogen pollution of water, the study aimed to isolate high-yield protease producing strains from artificially cultivated Monopterus albus, which will provide strain resources for the production of microbial proteases and the development of probiotics in the future. High-yield protease producing strains were preliminarily isolated from the artificially cultivated Monopterus albus by the combination of the transparent circle method of skimmed milk powder culture medium for primary screening and the Folin-phenol method for secondary screening to measure protease activity. The safety of the strains was tested through a hemolysis test and a drug sensitivity test, and the strains were identified by adopting a combination method of the physiological and biochemical characteristics of the strain. The fermentation conditions for protease production were optimized through single factor and orthogonal experiments. A high-yield protease producing strain named Ma-4 was screened, and it was identified as Bacillus aryabhattai, which can also produce the hydrogen peroxide enzyme. Its optimal enzyme production conditions were the fermentation time of 48 h, the fermentation temperature of 36, the optimal amount of soluble starch of 15 g/L, the optimal amount of beef powder of 15 g/L, and the pH value of 6.0. After optimization, the enzyme activity increased to 288.14 U/mL, representing a 3.34-fold improvement. The study indicates that the strain Ma-4 is a high protease-producing, catalase-producing, non-hemolytic and drug-resistant Bacillus aryabhattai, which can provide strain resources for the development of micro-ecological preparations of Monopterus albus. [ABSTRACT FROM AUTHOR]

This study investigates the effects of soybean lecithin (SL) on the growth, fatty acid composition, lipid metabolism, and gonadal development of rice field eels. Fourteen-month-old eels were fed either fish oil diets or varying levels of dietary soybean lecithin (0 %, 1.4 %, and 2.8 %) for 10 weeks. Dietary SL had no significant impact on growth, whereas 1.4 % SL led to a significant decrease in moisture content and an increase in crude protein content in eels. The content of both saturated and polyunsaturated fatty acids increased in muscles fed the higher SL diet, with a concurrent decline in saturated fatty acids and an increase in polyunsaturated fatty acids detected in the liver. The expression levels of genes related to lipid synthesis, including accα and PPARγ, and genes related to polyunsaturated fatty acid synthesis, such as pla2g4a, fad2 and scd, were significantly increased in the liver of eels fed with 1.4 % SL diet. SL supplementation enhances lipid transport and antioxidant capacity in the liver, reduces fat deposition, and protects the liver from damage. Hepatosomatic index of fish in the SL1.4 % and SL2.8 % groups decreased. Supplementation of the diet with 1.4 % SL led to a significant decrease in the content of saturated fatty acids and an increase in the content of polyunsaturated fatty acids in the gonads, with a significant increase in arachidonic acid levels. The gonadosomatic index also increased with increasing dietary SL content. Rice field eels fed diets containing SL exhibited elevated serum levels of E2, delayed ovary-to-testis transition, and a preference for retaining the female state. In conclusion, dietary supplementation with SL increased the proportion of highly unsaturated fatty acids in the tissues, enhanced lipid metabolism in the liver, and improved antioxidant capacity. Furthermore, SL supplementation has been demonstrated to promote ovarian development and delay sex reversal in rice field eels.

Introduction and Objectives: To date, there are no known supplement products made from a combination of eel and tempe. The development of concentrate from eels in combination with tempe (ETF) aims to create supplements containing the essential amino acid L-arginine, which has many proven health benefits. Methods: The community empowerment was held from June to July 2023 at Cangkringan, Sleman, Yogyakarta. The main agendas consisted of ETF training production and the cooking creation of ETF-based food. Aside from that, there were several secondary agendas such as food halal socialization, accessories design training, patchwork utilization training, computer and Microsoft Office training, English language education, public speaking class, Al-Qur’an and miscellaneous education for children, community service, mutual cinema, and competitions for the community. Results: The community development program in the production of high-amino acid concentrated ETF flour has succeeded in achieving the three main objectives of the program, namely functional product innovation, empowerment of micro, small, and medium enterprises and local communities, as well as increasing demand for local commodities, showing the importance of collaboration between the government, community, and private sector in supporting the development of local products that are economically and health-beneficial and can be used as examples to share similar initiatives in other areas. [ABSTRACT FROM AUTHOR]

Copyright of South China Fisheries Science is the property of South China Fisheries Science Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Gonadotropin-inhibitory hormone (GnIH) is a hypothalamic neuropeptide known for inhibiting gonadotropin release. In teleosts, it is also referred to as LPXRFa. While the effects of LPXRFa on gonadotropin synthesis and release, and its impact on pituitary function in teleosts have been widely studied, its specific mechanism in fish reproduction remains relatively unexplored. In this paper, LPXRFa and LPXRFa-R genes were isolated from the swamp eel brain to assess the roles of LPXRFa in the swamp eel. Their ORFs were 612 bp and 1284 bp, encoding proteins of 203 and 427 amino acids, respectively. The LPXRFa gene encodes a polypeptide possibly cleaved into three mature peptides (LPXRFa-1, −2, and −3). The LPXRFa-R receptor protein comprises seven conserved transmembrane domains. Tissue distribution analysis revealed that LPXRFa-R expression was the highest in the hypothalamus, while LPXRFa showed the highest expression in the rest of brain, with little to no expression in other tissues. The role of LPXRFa in the reproduction of the swamp eel was investigated by studying the effect of intraperitoneal injection with each of the three peptides. The intraperitoneal injection of LPXRFa-2 down-regulated serum FSH and LH levels, while that of LPXRFa-3 down-regulated serum FSH but up-regulated LH levels. Additionally, both LPXRFa-2 and LPXRFa-3 increased the expression levels of fshr, cbx3, dmrt1, gsdf, sox9al, amh, foxl2, and rab37 in the ovaries. Moreover, LPXRFa-2 also increased the ovarian expression of lhr, while LPXRFa-3 had no effect on it. Except upregulating cbx3 and foxl2 expression, LPXRFa-1 neither impacted the serum FSH and LH levels, nor did it alter the expression of other gonadal and reproductive-related genes. In summary, our findings provide the first evidence of a LPXRFa/LPXRFa-R system in the order Synbranchiformes and suggest its involvement in sex differentiation, gonadal development, and sexual reversal in the swamp eel.

Abstract Background Monopterus albus is a hermaphroditic fish with sex reversal from ovaries to testes via the ovotestes in the process of gonadal development, but the molecular mechanism of the sex reversal was unknown. Methods We produced transcriptomes containing mRNAs and lncRNAs in the crucial stages of the gonad, including the ovary, ovotestis and testis. The expression of the crucial lncRNAs and their target genes was detected using qRT‒PCR and in situ hybridization. The methylation level and activity of the lncRNA promoter were analysed by applying bisulfite sequencing PCR and dual-luciferase reporter assays, respectively. Results This effort revealed that gonadal development was a dynamic expression change. Regulatory networks of lncRNAs and their target genes were constructed through integrated analysis of lncRNA and mRNA data. The expression and DNA methylation of the lncRNAs MSTRG.38036 and MSTRG.12998 and their target genes Psmβ8 and Ptk2β were detected in developing gonads and sex reversal gonads. The results showed that lncRNAs and their target genes exhibited consistent expression profiles and that the DNA methylation levels were negatively regulated lncRNA expression. Furthermore, we found that Ptk2β probably regulates cyp19a1 expression via the Ptk2β/EGFR/STAT3 pathway to reprogram sex differentiation. Conclusions This study provides novel insight from lncRNA to explore the potential molecular mechanism by which DNA methylation regulates lncRNA expression to facilitate target gene transcription to reprogram sex differentiation in M. albus, which will also enrich the sex differentiation mechanism of teleosts.

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.

10-week dietary arachidonic acid (ARA) feeding trials were conducted in 14-month-old swamp eel (Monopterus albus) to evaluate the effects on growth performance, gonadal development, tissue fatty acid profile, and gene expression related to lipid metabolism. The results showed that swamp eels fed diets supplemented with 1.4% or 2.8% ARA had a significantly higher weight gain rate (WGR) and specific growth rate (SGR) than those fed the control diet. Dietary supplementation with ARA improved oocyte development and maturation. Higher gonadosomatic index (GSI) was detected in 1.4% and 2.8% ARA groups. ARA supplementation delayed sexual reversal in females. The ARA content in the muscle, liver and gonads increased with increasing dietary ARA concentration; however, ARA supplementation significantly reduced the transcriptional expression of lipid metabolism-related genes in the gonads, such as fad2, pla2g4a, and elovl5. Serum alanine aminotransferase (ALT) levels in the ARA 1.4% group were significantly lower than those in the control and ARA 2.8% groups. Total cholesterol (T-CHO) and triglyceride (TG) levels were significantly lower in the 1.4% and 2.8% ARA groups than in the control group. Catalase (CAT) and high-density lipoprotein cholesterol (HDL-C) increased with dietary ARA concentrations. This study found that dietary ARA is important for improving growth, Ovarian development, and antioxidant capacity in swamp eels.

This work investigated the effect of spray drying parameters on the physicochemical properties and oxidative stability of oil from menhaden (Brevoortia spp.) and Asian swamp eel (Monopterus albus) oil microcapsules. Different emulsion formulations (Maltodextrin - MD, Maltodextrin+Gum Arabic - MD+GA, and Maltodextrin+Starch - M+S), inlet air temperatures (180, 190, and 200 °C), and feed flow rates (280, 382, and 485 mL/h) were applied to microencapsulate Brevoortia spp. oil. The best operating parameters were then used to microencapsulate the Monopterus albus oil. The moisture content, MC (%), peroxide value, PV (mEq/kg), free fatty acid, FFA (%), acid value, AV (mg KOH/g) and the morphology of the microcapsules were then evaluated. The Brevoortia spp. oil microcapsules produced with the Maltodextrin+Gum Arabic emulsion formulation, inlet air temperature of 200 °C, and feed flow rate of 280 mL/h showed the lowest moisture content, peroxide value, free fatty acid, and acid value of 9.145%, 3.293 mEq/kg, 4.891%, and 2.981 mg KOH/g, respectively. Using similar parameters, the microencapsulation of the Monopterus albus oil extract recorded a moisture content, peroxide value, free fatty acid, and acid value of 8.432%, 2.713 mEq/kg, 4.911%, and 2.871 mg KOH/g, respectively. In conclusion, improved physicochemical properties and oxidative stability of Monopterus albus oil extract microcapsules were achieved using the Maltodextrin+Gum Arabic emulsion formulation and spray drying at a high air inlet temperature of 200 °C and a low feed flow rate of 280 mL/h.

The swamp eel (Monopterus albus) is a commonly cultured freshwater fish. Selection and cultivation of fecund broodstock is crucial for efficient artificial reproduction in this species. However, there are currently no guidelines for selecting high-quality males in M. albus. This study quantitatively investigated the sperm motility of male swamp eels during the breeding season by using computer-assisted sperm analysis system. Variability in the proportion and number of motile sperm was observed between individual males. The testes were grouped into high-quality and low-quality according to sperm quality. Morphometric parameters of the two groups were analyzed. We found that high-quality testes were longer (150 ± 27 mm verses 127 ± 19 mm) than low-quality testes. Besides, the proportion of testes with a dark appearance was slightly higher (58.3% verses 48.1%) in the high-quality group than in the low-quality group. Metabolomic analysis was conducted to compare the metabolite profiles of high-quality and low-quality testes. Glycerophospholipids, organic acids, glycerolipids, amino acids, sphingolipids, and nucleotides were the most abundant metabolites in the testes of swamp eels. Moreover, 135 differential metabolites were identified. Several nucleotide derivatives, including 50-deoxyadenosine, 20-deoxyadenosine, and ribosyl adenosine, were the most significantly enriched metabolites in highquality testes. These metabolites are potential indicators for the testis quality in M. albus. Altogether, our work provides systematic and quantitative data about the physiological and biochemical characteristics of M. albus testis, which provides an evidential basis for the selection of high-fecundity parents to improve artificial reproduction efficiency of M. albus. [ABSTRACT FROM AUTHOR]

The neuropeptide B/W signaling system is composed of neuropeptide B (NPB), neuropeptide W (NPW), and two cognate receptors, NPBWR1 and NPBWR2, which are involved in diverse physiological processes, including the central regulation of neuroendocrine axes in vertebrates. The components of this signaling system are not well conserved during vertebrate evolution, implicating its functional diversity. The present study characterized the ricefield eel neuropeptide B/W system, generated a specific antiserum against the neuropeptide B/W receptor, and examined the potential roles of the system in the regulation of adenohypophysial functions. The ricefield eel genome contains npba, npbb, and npbwr2b but lacks the npw, npbwr1, and npbwr2a genes. The loss of npw and npbwr1 probably occurred at the base of ray-finned fish radiation and that of npbwr2a species specifically in ray-finned fish. Npba and npbb genes are produced through whole-genome duplication (WGD) in ray-finned fish. The ricefield eel npba was expressed in the brain and some peripheral tissues, while npbb was predominantly expressed in the brain. The ricefield eel npbwr2b was also expressed in the brain and in some peripheral tissues, such as the pituitary, gonad, heart, and eye. Immunoreactive Npbwr2b was shown to be localized to Lh and Fsh cells but not to Gh or Prl cells in the pituitary of ricefield eels. Npba upregulated the expression of fshb and cga but not lhb mRNA in pituitary fragments of ricefield eels cultured in vitro. The results of the present study suggest that the NPB system of ricefield eels may be involved in the neuroendocrine regulation of reproduction. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

To understand the effects of vitamin A on lipid deposition in rice field eels, integrated liver transcriptome and metabolome were conducted and the changes in the genes andmetabolites were assessed. Three groups of rice field eel were fedwith 0, 200, and 16,000 IU/kg vitamin A supplementations in their diets for 70 days. The total lipid content in the whole body of the rice field eels was significantly increased with the vitamin A supplementations (p < 0.05). Comparative transcriptome analysis revealed 14 pathways and 46 differentially expressed genes involved in lipid metabolism. Sphingolipid metabolism, glycerolipid metabolism, primary bile acid biosynthesis and steroid hormone biosynthesis were significantly enriched pathways. In these pathways, three differential genes phospholipid phosphatase 1a (PLPP1a), phospholipid phosphatase 2b (PLPP2b), cytochrome P450 21a2 (CYP21a2) were consistent with the change trend of lipid content, and the other three differential genes aldo-keto reductase family 1 member D1 (AKR1D1), uridine diphosphate glucuronic acid transferase 1a1 (UGT1a1), cytochrome P450 1a (CYP1a) were opposite. Metabolomic analysis revealed that primary bile acid biosynthesis, sphingolipid metabolism, steroid hormone biosynthesis and biosynthesis of unsaturated fatty acids were all critical for rice field eel metabolic changes in response to vitamin A. Six important differential metabolites (eicosapentaenoic acid, sphinganine, 11-beta-hydroxyprogesterone, hydroxyeicosatetraenoic acid, cholic acid, and glycochenodeoxycholate) were identified and have provided new insights into how vitamin A regulates lipid deposition. Integrated transcriptome and metabolome analyses revealed that primary bile acid biosynthesis was the only remarkably enriched pathway in both the transcriptome and metabolome while that sphingosine was the main metabolite. Based on the above results, we have concluded that vitamin A promotes lipid deposition in the rice field eel through the primary bile acid synthesis pathway, and lipid deposits are widely stored in cell membranes, mainly in the form of sphingosine. These results will provide reference data to help improve our understanding of how vitamin A regulates lipid metabolism. [ABSTRACT FROM AUTHOR]

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An eight-week feeding trial explored the mechanism of methionine supplementation (0 g/kg, 4 g/kg, 8 g/kg, 12 g/kg) in a high-fat diet (120 g/kg fat, HFD) on the growth performance and hepatic lipid metabolism of M. albus (initial weight 25.03 ± 0.13 g) based on a basic diet (60 g/kg fat), named as Con, HFD+M0, HFD+M4, HFD+M8, HFD+M12, respectively. 1) Compared with Con, high-fat diet decreased the survival rate and weight gain rate of M. albus, and significantly enhanced the feed conversion rate, hepatopancreas index and crude lipid content of M. albus (P

Lipid is an important source of energy in fish feeds, and the appropriate fat content can improve the efficiency of protein utilization. However, excessive lipid content in the feed can lead to abnormal fat deposition in fish, which has a negative effect on the growth of fish. Therefore, the effects of feed lipid levels on swamp eel were studied. Essential functional genes were screened using transcriptomics. We divided 840 fish into seven groups (four replicates). A mixture of fish and soybean oils (1:4), 0%, 2%, 4%, 6%, 8%, 10%, and 12% was added to the basic feed were named groups one to seven (L1-L7), respectively. Isonitrogenous diets were fed swamp eel for 10 weeks. Growth performance, visceral index, nutritional components, and biochemical indexes were measured and analyzed. Livers of the 0%, 6%, and 12% groups were subjected to transcriptome sequencing analysis. The results of our study showed that: the suitable lipid level for the growth of swamp eel was 7.03%; the crude fat content of whole fish, liver, intestine, muscle, and skin increased with the increase of lipid level, with some significant difference, and excess fat was deposited in skin tissue; triglyceride, total cholesterol, and free fatty acid contents increased with the increase of feed lipid level. High-density lipoprotein levels in the L3 and L4 groups were higher than in the other groups. Blood glucose concentrations in the L5, L6, and L7 groups increased; the liver tissue structure was damaged when the lipid level was too high. two-hundred-and-twenty-eight differentially expressed genes were found. Several critical pathways regulating glucose metabolism and energy balance (e.g., glycerolipid metabolism, glycolysis synthesis, degradation of ketone bodies, and Janus Kinase/Signal Transducer and Activator of Transcription signaling pathway) were enriched in swamp eel compared with the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. Suitable lipid levels (7.03%) can promote the growth of swamp eel, and excessive lipid levels can cause elevated blood lipids and lead to liver cell damage. Regulatory mechanisms may involve multiple metabolic pathways for glucose and lipid metabolism in eels. This study provides new insights to explain the mechanism of fat deposition due to high levels of lipid and provides a basis for the production of efficient and environmentally friendly feed for swamp eel. [ABSTRACT FROM AUTHOR]

The experiment was conducted to investigate the effect of Se-Met supplementation on growth performance, selenium content in muscle tissue and serum biochemical indexes of Monopterus albus. Three hundred Monopterus albus with body weight of (27.55±0.85) g were randomly divided into five groups, with three replicates in each group and 20 Monopterus albus in each replicate. The Monopterus albus in control group were fed with basal diet, and Monopterus albus in SM1 group, SM2 group, SM3 group and SM4 group were fed with basal diet supplemented with 0.3, 0.6, 0.9 and 1.5 mg/kg Se-Met, respectively. The experiment lasted for 21 d. The results showed that compared with control group, the weight gain rate of Monopterus albus in SM2 group was significantly increased (P<0.05), and the feed coefficient was decreased (P<0.05). The content of selenium in muscle tissue of Monopterus albus in SM2 group, SM3 group and SM4 group was significantly higher than that in control group (P<0.05). The serum total cholesterol content of Monopterus albus in Se-Met groups was significantly higher than that in control group (P<0.05), the content of total cholesterol and high density lipoprotein cholesterol in SM2 group were the highest, and the content of low density lipoprotein cholesterol in SM4 group was significantly higher than that in other groups (P<0.05). The activity of serum alkaline phosphatase, glutamyltransferase, aspartate aminotransferase and alanine aminotransferase in Se-Met groups were higher than those in control group, and the activity of SM4 group was the highest. Serum IgM content of Monopterus albus in Se-Met supplemental groups was higher than that in control group. The experiment indicates that adding proper amount of Se-Met in diet can improve the growth performance, immune function and selenium content in muscle tissue of Monopterus albus, and the optimal supplemental level is 0.6 mg/kg. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Hydrobiology is the property of Editorial Department of Journal of Hydrobiology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The swamp eel, Monopterus albus, is an important aquaculture species in Asia (mainly China) whose production has seriously suffered from infectious diseases. In spite of the critical requirement for aquaculture practices, to date there is scant information on its immune defence. Here, the genetic characteristics of Toll‐like receptor 9 (TLR9), which plays crucial roles in the initiation of host defence against microbial invasion, were analysed. It exhibits a striking lack of genetic variation resulting from a recent demographic bottleneck. A comparison with the homologue of M. javanensis revealed that replacement but not silent differences have nonrandomly accumulated in the coding sequences at the early stage following their split from a common ancestor. Furthermore, the replacements relevant to the type II functional divergence have mainly occurred in structural motifs mediating ligand recognition and receptor homodimerization. These results provide hints to understand the diversity‐based strategy of TLR9 in the arms race against pathogens. Furthermore, the findings reported here give credence to the importance of basic immunology knowledge, especially for the key elements, in genetic engineering and breeding for disease resistance in the eel and other fishes. [ABSTRACT FROM AUTHOR]

Highlights DNA methylation modification plays a more crucial role than chromatin accessibility in gonad development. DNA methylation in the transcription start site plays a key role in gonad development. DNA methylation of the plastin-2 promoter inhibited gene expression. Plastin-2 is positively regulated by dmrt1 while negatively regulated by foxl2.

Abstract Background The expression and biological functions of circular RNAs (circRNAs) in reproductive organs have been extensively reported. However, it is still unclear whether circRNAs are involved in sex change. To this end, RNA sequencing (RNA-seq) was performed in gonads at 5 sexual stages (ovary, early intersexual stage gonad, middle intersexual stage gonad, late intersexual stage gonad, and testis) of ricefield eel, and the expression profiles and potential functions of circRNAs were studied. Results Seven hundred twenty-one circRNAs were identified, and the expression levels of 10 circRNAs 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. Then, the sequence length, category, sequence composition and the relationship between the parent genes of the circRNAs were explored. A total of 147 circRNAs were differentially expressed in the sex change process, and GO and KEGG analyses revealed that some differentially expressed (such as novel_circ_0000659, novel_circ_0004005 and novel_circ_0005865) circRNAs were closely involved in sex change. Furthermore, expression pattern analysis demonstrated that both circSnd1 and foxl2 were downregulated in the process of sex change, which was contrary to mal-miR-135b. Finally, dual-luciferase reporter assay and RNA immunoprecipitation showed that circSnd1 and foxl2 can combine with mal-miR-135b and mal-miR-135c. These data revealed that circSnd1 regulates foxl2 expression in the sex change of ricefield eel by acting as a sponge of mal-miR-135b/c. Conclusion Our results are the first to demonstrate that circRNAs have potential effects on sex change in ricefield eel; and circSnd1 could regulate foxl2 expression in the sex change of ricefield eel by acting as a sponge of mal-miR-135b/c. These data will be useful for enhancing our understanding of sequential hermaphroditism and sex change in ricefield eel or other teleosts.

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Abstract Background An increasing number of long noncoding RNAs (lncRNAs) have been found to play important roles in sex differentiation and gonad development by regulating gene expression at the epigenetic, transcriptional and posttranscriptional levels. The ricefield eel, Monopterus albus, is a protogynous hermaphroditic fish that undergoes a sequential sex change from female to male. However, the roles of lncRNA in the sex change is unclear. Results Herein, we performed RNA sequencing to analyse lncRNA expression patterns in five different stages of M. albus development to investigate the roles of lncRNAs in the sex change process. A total of 12,746 lncRNAs (1503 known lncRNAs and 11,243 new lncRNAs) and 2901 differentially expressed lncRNAs (DE-lncRNAs) were identified in the gonads. The target genes of the DE-lncRNAs included foxo1, foxm1, smad3, foxr1, camk4, ar and tgfb3, which were mainly enriched in signalling pathways related to gonadal development, such as the insulin signalling pathway, MAPK signalling pathway, and calcium signalling pathway. We selected 5 highly expressed DE-lncRNAs (LOC109952131, LOC109953466, LOC109954337, LOC109954360 and LOC109958454) for full length amplification and expression pattern verification. They were all expressed at higher levels in ovaries and intersex gonads than in testes, and exhibited specific time-dependent expression in ovarian tissue incubated with follicle-stimulating hormone (FSH) and human chorionic gonadotropin (hCG). The results of quantitative real-time PCR (qRT-PCR) analysis and a dual-luciferase assay showed that znf207, as the gene targeted by LOC109958454, was expressed in multiple tissues and gonadal developmental stages of M. albus, and its expression was also inhibited by the hormones FSH and hCG. Conclusions These results provide new insights into the role of lncRNAs in gonad development, especially regarding natural sex changes in fish, which will be useful for enhancing our understanding of sequential hermaphroditism and sex changes in the ricefield eel (M. albus) and other teleosts.

Metamifop (MET) is a widely used herbicide. It is likely for it to enter water environment when utilized, thus potential impacts may be produced on aquatic animals. Little information is available about its effects on the endocrine system of fish to date. In the current study, female rice field eels (Monopterus albus) were exposed to different MET concentrations (0, 0.2, 0.4, 0.6, 0.8 mg L −1) for 96 h to examine the effect of MET on the hypothalamic-pituitary-gonadal (HPG) axis and sexual reversal. The results showed that high concentrations of MET exposure increased vitellogenin (VTG) levels in liver and plasma, but plasma sex hormone levels were not affected by MET exposure. MET exposure increased the expression of CYP19A1b and CYP17 that regulate sex hormone production in the brain, but the expression of genes (CYP19A1a, CYP17, FSHR, LHCGR, hsd11b2, 3β-HSD) associated with sex hormone secretion in the ovary and the estrogen receptor genes (esr1, esr2a, esr2b) in the liver were all suppressed. In addition, the expression of sexrelated gene (Dmrt1) was suppressed. This study revealed for the first time that MET has estrogen-like effects and has a strong interference with the expression of HPG axis genes. MET did not show the ability to promote the sexual reversal in M. albus, on the contrary, the genes expression showed that the occurrence of male pathway was inhibited. [ABSTRACT FROM AUTHOR]

Swamp eel (Monopterus albus) is one of the most important cultured fresh water species with high economic value in China, however, the present compound diets could not meet the growth and gonad development of swamp eel broodstocks, which hampered the large-scaled aquaculture of this species, therefore, the reproduction improvement of swamp eels by optimization of the compound diet formulation is on the urgent need. Antarctic krill meal is rich in sustainable resources and has the same nutritional level as fish meal, which meets the requirements of a new type of animal protein source for feed. Reports showed that Antarctic krill meal inclusion improved the growth and reproduction of several aquatic animals. In this study, two-winter-age female Monopterus albus with an initial body weight of (36.41±3.62) g was adopted. Antarctic krill meal was included to replace 0, 20%, 40%, 60%, 80%, and 100% fish meal to make 6 groups of iso-nitrogenous and iso-energetic diets. After 12 weeks of culture, the growth performance, body composition, hepatic anti-oxidant capacity and non-specific immunity, and fecundity of six groups of experimental eels were determined. The results showed that the weight gain rate (WGR) and specific growth rate (SGR) of eels had no significant differences in 20% replacement group and the control group (P>0.05). However, the further increase of Antarctic krill meal substitution (>40%) led to the growth performance reduction. In muscle, crude protein concentration was higher in 20% substitution group than the other experimental groups; no significant differences were observed in the crude lipid and ash concentrations among different groups in muscle of swamp eels (P>0.05). In ovary, the nutrient composition had no significant difference between groups of 20% substitution group and the control group (P>0.05). Concentrations of crude protein and crude lipid decreased significantly while the moisture concentration increased gradually by Antarctic krill meal substitution from 60% to 100%. The further detection of the anti-oxidant capacity of liver revealed that superoxide dismutase (SOD) activity decreased gradually albeit with the increase of malondialde-hyde (MDA) concentration in groups of Antarctic krill meal substitution higher than 40%. The catalase (CAT) activity in 100% substitution group was lower than the other five groups. The following non-specific immunity evaluation of liver suggested that no significant differences were observed between 20% substitution group and the control group in parameters of alkaline phosphatase (AKP), complement 4 (C4), and immunoglobulin M (IgM) (P>0.05). When the Antarctic krill meal substitution level were 60% or higher, the AKP activity showed the increased trend, while concentrations of C4 and IgM decreased instead. Lastly, fecundity of swamp eels in all groups were examined. The 20% Antarctic krill meal substitution did not influence fecundity parameters including gonadosomatic index (GSI), absolute fecundity, relative fecundity and serum estradiol concentration (P>0.05) in swamp eels. GSI in 80% and 100% groups were lower than that of 40% and 60% groups. From 60% to 100% substitution groups, the absolute fecundity, relative fecundity and estradiol concentrations decreased gradually with the increase of Antarctic krill meal inclusion. Egg diameters increased gradually with the increase of krill meal inclusions, but significant differences were only found from 100% group to groups of 0 and 20% (P<0.05). From the above results, it showed that the growth performance, ovarian nutrient composition, hepatic anti-oxidant capacity and non-specific immunity, and fecundity will not be influenced when 20% fish meal were replaced by Antarctic krill meal in diets of female swamp eels. Higher substitutions of Antarctic krill meal will intensify the adverse effect on this fish species. Therefore, the substitution of Antarctic krill meal of fish meal should not exceed 20% in formulated diets of female Monopterus albus. [ABSTRACT FROM AUTHOR]

Background: Monopterus albus is a hermaphroditic and economically farmed fish that undergoes sex reversal from ovary to testis via ovotestis during gonadal development. The epigenetic changes that are associated with gonadal development in this species remain unclear. Methods: We produced DNA methylome, transcriptome, and chromatin accessibility maps of the key stages of gonad development: ovary, ovotestis, and testis. The expression of the key candidate genes was detected using qRT-PCR and in situ hybridization and the methylation levels were analysed using bisulphite sequencing PCR. Promoter activity and regulation were assessed using dual-luciferase reporter assays. Results: Gonadal development exhibits highly dynamic transcriptomic, DNA methylation, and chromatin accessibility changes. We found that DNA methylation status, especially of the transcription start site, was significantly negatively correlated with gene expression while chromatin accessibility exhibited no correlation with gene expression during gonadal development. The epigenetic signatures revealed many novel regulatory elements and genes involved in sex reversal, which were validated. DNA methylation detection and site mutation of plastin-2 promoter, as a candidate gene, revealed that DNA methylation could impact the binding of transcription factor dmrt1 and foxl2 through methylation and demethylation to regulate plastin-2 expression during gonadal development. Conclusions: These data provide novel insights into epigenetic modification and help elucidate the potential molecular mechanism by which dynamic modification of DNA methylation plays a crucial role in gonadal development. Highlights: DNA methylation modification plays a more crucial role than chromatin accessibility in gonad development. DNA methylation in the transcription start site plays a key role in gonad development. DNA methylation of the plastin-2 promoter inhibited gene expression. Plastin-2 is positively regulated by dmrt1 while negatively regulated by foxl2. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Corbicula fluminea meal was added to a high-fat diet for eight weeks to determine its effects on growth, lipid metabolism, and intestinal microbiota in juvenile rice field eel (Monopterus albus). C. fluminea meal was made of dried and crushed soft parts of freshwater clam. The study included four diets: a normal fat diet (6.63% lipid, CON), a high fat diet (12.61% lipid, HFD), and a high fat diet supplemented with 1% or 2% C. fluminea meal (CFM1 and CFM2, respectively). The results showed that: (1) the growth performance was higher in the HFD, CFM1 and CFM2 group compared with the CON group, the hepatosomatic index (HSI) was significantly higher in fish fed the high-fat diet than in those fed other diets. (2) Compared with the CON group, The levels of serum triacylglycerol (TG), low-density lipoprotein cholesterol (LDL-C) contents, glutamate pyruvic transaminase (GPT), glutamic oxaloacetic transaminase (GOT) activities and the number of hepatic lipid droplets were significantly increased in the HFD group. The addition of C. fluminea meal both reduced liver damage and fat deposition. (3) The mRNA expressions of pparγ , fas , acc , me1 , srebp1 , g6pdh , hsl , lpl , cpt1, and cpt2 in the HFD group were significantly upregulated, while HFD supplemented with C. fluminea meal significantly downregulated the mRNA expressions of pparγ , fas , acc , me1 , srebp1 and g6pdh and significantly upregulated the mRNA expressions of hsl and lpl. (4) The alpha diversity of intestinal microbial community in the HFD group was higher than those in the CON and CFM1 groups. The beta diversity revealed the microbial composition differed in the HFD group from the CON and CFM1 groups. The abundance of Firmicutes in the HFD group increased significantly compared with the CON and CFM1 groups, while the abundances of Cetobacterium decreased. In conclusion, the high-fat diet resulted in abnormal liver fat deposits and intestinal microbiota dysfunction in M. albus , but HFD supplemented with 1% or 2% C. fluminea meal reduced these negative effects. • The effects of high-fat feed on lipid metabolism and intestinal flora of eels were revealed. • 1% or 2% C. fluminea meal can mitigated the negative effects of high-fat feeds on the liver. • 1% C. fluminea meal improving the intestinal flora structure of eel. • C. fluminea meal may play a vital role in liver protection and energy metabolism of eels. [ABSTRACT FROM AUTHOR]

Toll-like receptor 1 (TLR1) is a pattern recognition receptor that plays critical roles in triggering immune activation via detecting bacterial lipoproteins and lipopeptides. In this study, the genetic characteristic of TLR1 was studied for an important aquaculture fish, swamp eel Monopterus albus. The eel has been seriously threatened by infectious diseases. However, a low level of genetic heterogeneity in the fish that has resulted from a demographic bottleneck presents further challenges in breeding for disease resistance. A comparison with the homologue of closely related species M. javanensis revealed that amino acid replacement (nonsynonymous) but not silent (synonymous) differences have accumulated nonrandomly over the coding sequences of the receptors at the early stage of their phylogenetic split. The combined results from comparative analyses of nonsynonymous-to-synonymous polymorphisms showed that the receptor has undergone significant diversification in M. albus driven by adaptive selection likely after the genetic bottleneck. Some of the changes reported here have taken place in the structures mediating heterodimerization with co-receptor TLR2, ligand recognition, and/or formation of active signaling complex with adaptor, which highlighted key structural elements and strategies of TLR1 in arms race against exogenous challenges. The findings of this study will add to the knowledge base of genetic engineering and breeding for disease resistance in the eel. • Genetic characteristic of immune receptor TLR1 was studied for Monopterus albus. • M. albus TLR1 gained conspicuous genetic diversity at different evolutionary stages. • Diversity occurred nonrandomly over TLR1 in early M. albus - M. javanensis split. • M. albus TLR1 underwent significant diversification after recent genetic bottleneck. • Some diverse changes lie in or adjacent to structures mediating essential functions. [ABSTRACT FROM AUTHOR]

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.

An 8-weeks feeding experiment was performed to evaluate the potential effect of dietary taurine on the growth, liver oxidative stress and lipid metabolism, intestinal integrity and inflammatory response as well as the skin pigments of Monopterus albus fed with the oxidized fish oil diet. With that purpose, four iso-nitrogenous and iso-lipid experimental diets were formulated, including FO (2% fresh fish oil), OO (2% oxidized fish oil completely replacing the fresh fish oil in FO group) supplemented with 0%, 0.2% (OOT0.2) and 0.5% (OOT0.5) taurine. Each diet was randomly fed to triplicate groups of 50 fish (average initial weight 30.09 ± 0.06 g). The results showed that long-term feeding of OO diet did not affect the growth performance, while decreased the contents of serum immune parameters, lowered the liver antioxidative enzymes activities and induced oxidative stress, caused abnormal fat deposition in liver by interfering lipid metabolism-related genes mRNA express profile, simultaneously accompanied by hepatocyte atrophy, destroyed the intestinal mucosal barrier through dysregulation of the mRNA expression of tight junction proteins and raised the inflammatory response by elevating the pro-inflammatory cytokines mRNA abundance, and generated undesirable skin hyperpigmentation via boosting tyrosinase activity. Notably, taurine administration improved the growth performance and partially mitigated the negative impacts in M. albus subjected to the oxidized fish oil. Taken together, it was supposed that taurine exerted its anti-oxidative and anti-inflammatory properties to confer protection against oxidized fish oil. These findings would provide a theoretical basis for the application of taurine in aquatic feed.

Apoptosis plays a key role in the effective removal of excessive and defective germ cells, which is essential for sequential hermaphroditism and sex change in vertebrates. The ricefield eel, Monopterus albus is a protogynous hermaphroditic fish that undergoes a sequential sex change from female to male. Previous studies have demonstrated that apoptosis is involved in sex change in M. albus. However, the apoptotic signaling pathway is unclear. In the current study, we explored the underlying mechanism of apoptosis during gonadal development and focused on the role of the mitochondrial apoptosis signaling pathway in sex change in M. albus. Flow cytometry was performed to detect apoptosis in gonads at five sexual stages and ovary tissues exposed to hydrogen peroxide (H2O2) in vitro. Then the expression patterns of key genes and proteins in the mitochondrial pathway, death receptor pathway and endoplasmic reticulum (ER) pathway were examined. The results showed that the apoptosis rate was significantly increased in the early intersexual stage and then decreased with the natural sex change from female to male. Quantitative real-time PCR revealed that bax, tnfr1, and calpain were mainly expressed in the five stages. ELISA demonstrated that the relative content of cytochrome-c (cyt-c) in the mitochondrial pathway was significantly higher than that of caspase8 and caspase12, with a peak in the early intersexual stage, while the levels of caspase8 and caspase12 peaked in the late intersexual stage. Interestingly, the Pearson's coefficient between cyt-c and the apoptosis rate was 0.705, which suggests that these factors are closely related during the gonadal development of M. albus. Furthermore, the cyt-c signal was found to be increased in the intersexual stage by immunohistochemistry. After incubation with H2O2, the mRNA expression of mitochondrial pathway molecules such as bax, apaf-1, and caspase3 increased in ovary tissues. In conclusion, the present results suggest that the mitochondrial apoptotic pathway may play a more important role than the other apoptotic pathways in sex change in M. albus. [ABSTRACT FROM AUTHOR]

Background: The expression and biological functions of circular RNAs (circRNAs) in reproductive organs have been extensively reported. However, it is still unclear whether circRNAs are involved in sex change. To this end, RNA sequencing (RNA-seq) was performed in gonads at 5 sexual stages (ovary, early intersexual stage gonad, middle intersexual stage gonad, late intersexual stage gonad, and testis) of ricefield eel, and the expression profiles and potential functions of circRNAs were studied. Results: Seven hundred twenty-one circRNAs were identified, and the expression levels of 10 circRNAs 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. Then, the sequence length, category, sequence composition and the relationship between the parent genes of the circRNAs were explored. A total of 147 circRNAs were differentially expressed in the sex change process, and GO and KEGG analyses revealed that some differentially expressed (such as novel_circ_0000659, novel_circ_0004005 and novel_circ_0005865) circRNAs were closely involved in sex change. Furthermore, expression pattern analysis demonstrated that both circSnd1 and foxl2 were downregulated in the process of sex change, which was contrary to mal-miR-135b. Finally, dual-luciferase reporter assay and RNA immunoprecipitation showed that circSnd1 and foxl2 can combine with mal-miR-135b and mal-miR-135c. These data revealed that circSnd1 regulates foxl2 expression in the sex change of ricefield eel by acting as a sponge of mal-miR-135b/c. Conclusion: Our results are the first to demonstrate that circRNAs have potential effects on sex change in ricefield eel; and circSnd1 could regulate foxl2 expression in the sex change of ricefield eel by acting as a sponge of mal-miR-135b/c. These data will be useful for enhancing our understanding of sequential hermaphroditism and sex change in ricefield eel or other teleosts. [ABSTRACT FROM AUTHOR]

Mannose receptor (MR), as a member of the C-type lectin (CLEC) family, plays an important role in the internalize pathogen-associated ligands and activate immune response. In the present study, MR was identified and characterized from Asian swamp eel (Monopterus albus) (namely Ma MR). The open reading frame of Ma MR was 4311 bp in length encoding 1437 amino acids of a ∼162.308 kDa protein, including a cysteine-rich (CR) domain, a fibronectin type II (FNII) domain, eight C-type lectin-like domains (CTLDs), a transmembrane domain and a short cytoplasmic domain. Phylogenetic analysis indicated that Ma MR shared the highest similarity with that of Paralichthys olivaceus. The expression of Ma MR was found in all the examined tissues, with the highest expression in the spleen and kidney. After injection with Edwardsiella tarda , the transcript level of Ma MR was initially reduced and then significantly elevated in the liver, spleen, foregut and hindgut. In the isolated peripheral blood leukocytes, the expression of Ma MR was significantly induced post stimulated with LPS and LTA. Then the Ma MR-CTLD4-8 recombinant protein was purified. Bacterial agglutination and binding assay showed that r Ma MR-CTLD4-8 could bind with both Gram-positive and Gram-negative bacteria and agglutinate bacteria in the presence of calcium in vitro. Further analysis revealed that Ma MR and TLR2 coordinately induced the expression of TRAF6 and promoted the phosphorylation level of p65, leading to the expression of proinflammatory cytokines il-1β and tnf-α in EPC cells. Taken together, these results reveal that Ma MR plays an important role in the immune response of fish to pathogen infections. • Mannose receptor (MR) was identified and characterized from Monopterus albus (namely Ma MR). • Ma MR was expressed in all examined tissues and could be induced by bacteria and PAMPs. • Ma MR can agglutinate and bind Gram-positive and -negative bacteria. • Ma MR induced the expression of proinflammatory cytokine with the assistance of TLR2. [ABSTRACT FROM AUTHOR]

In immature lymphocytes, recombination activating genes 1 and 2 are necessary for antigen receptor V (D) J recombination, representing immature lymphocyte biomarkers. Herein, we cloned and sequenced rice-field eel rag1 and rag2 genes. Their expressions in the thymus, liver, and kidney were significant from 0 days post hatching (dph) to 45 dph, peaking at 45 dph in these three tissues. In situ hybridization detected high rag1 and rag2 expressions in the liver, kidney, and thymus of rice-field eel from 2 to 45 dph, suggesting that multiple tissues of rice-field eel contain lymphocyte lineage cells and undergo lymphopoiesis. Tissue morphology was used to observe lymphopoiesis development in these three tissues. The thymus primordium began to develop at 2 dph, while the kidney and liver have generated. Our findings verified that the thymus is the primary lymphopoietic tissue and suggested that, in rice-field eel, lymphocyte differentiation also occurs in the liver and kidney. [ABSTRACT FROM AUTHOR]