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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]

Polyploid fish have valuable applications in aquaculture, and artificial breeding of polyploids is an important field of aquatic research. In this study, fertilized eggs (65–100 min post-fertilization (mpf)) were treated with 650–750 kg/cm2 hydrostatic pressure for 3–6 min to induce tetraploidy. The optimal rates for hatching and tetraploidization of embryos were achieved at 4.70% and 23.33%, correspondingly. Flow cytometry analysis revealed that the DNA content of tetraploidized embryo cells was approximately twice that of the wild-type. The chromosome number of the tetraploidized rice field eels was 48. In this study, artificially induced tetraploid rice field eels were able to survive, with four of them reaching 20 months of age. Measurement of erythrocyte nuclei revealed that the nuclear area of erythrocytes from tetraploids increased and was approximately twice that of the diploids. Histological analysis showed that the gonads of tetraploids developed into testes, and spermatogenetic germ cells were observed. In conclusion, a technique to induce tetraploidization has been developed for rice field eels by applying 700 or 750 kg/cm2 hydrostatic pressure on 85 mpf embryos for 5 min. The viable tetraploidized rice field eels were produced using this approach. • A method for hydrostatic pressure shock-induced tetraploid rice field eel was established. • Artificially induced tetraploid rice field eels survived and grow up to adult. • The gonad of tetraploid rice field eel developed into testis and may be fertile. [ABSTRACT FROM AUTHOR]

Abstract This study was conducted to determine the effect of different stocking densities on growth rate of Asian swamp eel (Monopterus albus), growth of watercress (Nasturtium officinale) in a floating-draft aquaponic recirculating system. Two factorial experiment designs consist of three different swamp eel (16.67 ± 3.48 g/individual) densities of 100, 180 and 260 individuals/m2 (8.4, 15.0 and 21.7 kg/m3, respectively) integrated with hydroponic trough of watercress (SEW) or without watercress (swamp eel only, SE). Watercress seeds were put into styrofoam, floating rack (80 heads/m2). Swamp eels were fed 2 times per day with commercial pellet (42% protein). The experiment was run for 65 days with two cycles of watercress. Statistical analysis by Two-way ANOVA showed that there is no significant difference (P >.05) in growth performance of swamp eel at different stocking densities between the SEW and SE systems. However, statistical analysis by One way ANOVA showed that there is a significant difference (P <.05) on weight gain (WG) and daily weight gain of animals among the SEW treatments. The highest WG was 32.78 ± 2.09 g/ind. and 41.71 ± 9.05 g/ind. for treatment of 180 inds./m2 at the SEW and SE, respectively. The average survival rate of animal in all treatments was above 80% and was not significant difference among the treatments. The lowest FCR (2.15 ± 0.94) were found in treatment 180 inds./m2 of the SEW. Production of watercress was low in all treatments, the highest biomass (507.81 ± 91.01 g/m2) was recorded for treatment 180 inds./m2 of the SEW. Nutrient accumulation was relatively high at higher stocking densities of swamp eel and was higher in the SE system compared to the SEW system. Total ammonia nitrogen (TAN) concentrations in the SE treatments were ranging from 2.61 ± 1.81 mg/L (120 ind./m2) to 5.77 ± 3.19 mg/L (260 ind./m2). Whereas, the TAN levels in the SEW treatments were only ranging from 1.94 ± 1.44 to 5.35 ± 0.36 mg/L and even lower in hydroponic trough (1.3–3.15 mg/L). Similarly, nitrate‑nitrogen level was high in the SE treatments (1.43 ± 1.36–2.36 ± 1.43 mg/L) and lower in the SEW treatments (0.89 ± 1.36–1.42 ± 1.34 mg/L). Generally, swamp eel farming combined with hydroponic trough was feasible in handling water quality and required little water change in contrast to SE treatments which required as much as 1 water change a day. This study found that the stocking density of 180 inds./m2 seems to be the most effective density for growth, survival of swamp eel as well as nutrient accumulation in the SEW. The results of this study provide an important information as to how aquaculture of swamp eel may be expanded in the Mekong Delta without destroying the environment by releasing nutrient rich effluent from growing chambers. Highlights • Higher stocking density of Asian swamp eel yielded relatively high production of Asian swamp eel. • Zero water discharged occurred in the aquaponic recirculating system of Asian swamp eel and watercress. • Nutrients accumulation rate varied depending on stocking densities of Asian swamp eel and biomass of watercress in the aquaponic recirculating system. • Initial stocking of 15.0 kg/m3 (180 ind./m2) swamp eel in the aquaponic recirculating system is recommended for production of swamp eel, watercress growth and nutrient reduction. • Aquaponic is a good perspective aquaculture system of Asian swamp eel regarding the environment issue. [ABSTRACT FROM AUTHOR]

Homozygous mutant populations are typically obtained when studying gene function using gene editing. However, because of asynchronous testicular and ovarian development, it is difficult to obtain homozygous mutant offspring of hermaphrodite fish by mating males and females. The rice field eel (Monopterus albus) was the first hermaphrodite teleost to be identified. Natural sex change characteristics render M. albus a good model for studying vertebrate sex differentiation. Rice field eels are also an economically important aquaculture species in East and Southeast Asia. In this study, we established a highly efficient multi-locus gene editing method for rice field eels. We selected cyp19a1a and foxl2 for editing and targeted seven and 11 sites in the coding regions of these genes, respectively. Fertilized eggs were co-injected with the Cas9 protein and the guide RNAs of each gene. The efficiency of gene editing–induced mutations in cyp19a1a and foxl2 was approximately 100% in the microinjected embryos and adult fish tissues. In cyp19a1a mutants, serum E 2 levels were decreased, and ovarian development was blocked. Only germ stem cells or oogonia were present in the gonads of the 12-month-old cyp19a1a mutant fish. These results suggest that cyp19a1a plays a key role in regulating primary gonadal development in the ovaries of rice field eels. In foxl2 mutants, cyp19a1a transcription and serum E 2 levels were minimally decreased, whereas the transcription of foxl2-l , foxl3 , and dmrt1 was increased. Nevertheless, the gonads of foxl2 mutant fish differentiated into ovaries, thereby indicating that foxl2 does not directly affect ovarian development in rice field eels. The multi-locus gene editing method established in this study provides an effective approach for studying gene function study and improving the genetic traits in rice field eels. • Multi-locus gene editing was performed in a hermaphroditic fish. • cyp19a1a and foxl2 was effectively knock out in Monopterus albus. • cyp19a1a plays a key role in regulating ovarian development in Monopterus albus. [ABSTRACT FROM AUTHOR]

This report described the cloning and gene expression pattern of cxcr4 paralogues, cxcr4a and cxcr4b, in Asian swamp eel Monopterus albus . The swamp eel cxcr4a cDNA contained a 1047 bp open reading frame encoding a deduced cxcr4a protein of 348 amino acids (aa) while cxcr4b had a 984 bp ORF coding for a 327 aa protein. Swamp eel cxcr4a and cxcr4b are members of G protein-coupled receptors with seven transmembrane domains. Cxcr4b from teleost is closer to tetrapod CXCR4 than to teleost cxcr4a. Like tetrapod CXCR4, all teleost cxcr4b genes have 2 exons and 1 intron. However, teleostean cxcr4a had 4–5 exons in the genomic DNA. Both cxcr4 genes had highest expression levels in the intestine and causal kidney. Stimulation with the Gram negative bacterium Aeromonas hydrophila in vivo and in vitro was able to modulate expression of cxcr4 paralogues. Poly I:C down-regulated cxcr4b expression of while it up-regulated cxcr4a expression. Acanthocephalan Pallisentis ( Neosentis ) celatus also increased the expression of swamp eel cxcr4 paralogues. Our data suggested that cxcr4 paralogues might play a significant role in the immune response of Asian swamp eel. Statement of relevance This report described cxcr4 paralogues and their modulation by pathogen infection, which is of significance in swamp eel aquaculture. [ABSTRACT FROM AUTHOR]

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. • The oocyte maturation stage was subdivided into GV1, GV2, GV3, and GVBD. • Transcriptomes of ovarian follicles were obtained to clarify molecular mechanisms. • Multiple cathepsins may be involved in vitellogenin hydrolysis in oocytes. • PDEs including Pde4b-like and Pde10 are possibly involved in meiotic resumption. [ABSTRACT FROM AUTHOR]

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. • Estradiol plays a key role in sex change of protogynous rice field eel. • Aromatase inhibitor treatment induces female to male sex reversal in juvenile rice field eel. • The aromatase inhibitor induced males had the equivalent fecundity with the wild males. [ABSTRACT FROM AUTHOR]

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. • Features of myofiber development in eels fed oxidized fish oil got explored. • Taurine reversed the negative effects of oxidized fish oil on muscle development. • Oxidized fish oil significantly affected muscle fatty acid composition. • Excessive autophagy induced by muscle oxidative stress led to myofiber loss. [ABSTRACT FROM AUTHOR]

A 8-week feeding trial was conducted to investigate the effects of the addition of taurine to a high-fat diet on growth performance, lipid deposition, antioxidant ability, and intestinal health in juvenile rice field eel (Monopterus albus). Four diets were designed: a normal fat diet (6.51% lipid, Control), high-fat diet (12.67% lipid, HFD), and high-fat diets supplemented with 0.2 and 0.5% taurine (HFD + T 0.2 and HFD + T 0.5 , respectively). The results showed that (1) the survival rate was significantly lower in fish fed a high-fat diet than in those fed other diets. The feed conversion rate in the HFD + T 0.5 group was markedly lower than that in the HFD group. (2) HFD-feeding significantly increased lipid deposition compared to that in the Control group. The addition of 0.2 or 0.5% taurine both ameliorated the HFD-induced increase in lipid droplets in the liver, significantly increased the hepatic lipase and lipoprotein lipase activities in serum, and decreased total cholesterol and triacylglycerol contents. (3) HFD-feeding significantly reduced serum immunity and antioxidant capacity. The HFD + T 0.2 and HFD + T 0.5 groups remarkably increased the levels of serum complement, lysozyme, alkaline phosphatase, glutathione, catalase, and superoxide dismutase. (4) The expression of pro-inflammatory cytokine (il-1β , il-12β , il-15 , tlr-3 , tlr-7 , tlr-8 , and nf-κb) in the HFD + T 0.2 and HFD + T 0.5 groups were significantly downregulated, while the expression of anti-inflammatory cytokines (il-10) and intestinal tight junction proteins (occludin and zo-2) were significantly upregulated. Beside, taurine supplementation at 0.2 or 0.5% both significantly decreased the nuclear NF-κB p65 protein level. In conclusion, high-fat diets induced negative effects in rice field eels, and dietary supplementation with 0.2 or 0.5% taurine can improve growth performance, decrease lipid deposition, enhance antioxidant ability, and maintain intestinal health. The best growth performance was seen in fish supplemented with 0.5% taurine. • High-fat diet decreased the survival rate and increased the lipid deposition of rice field eel. • High-fat diet had negative effects on the antioxidant capacity and intestinal health of rice field eel. • Taurine reduced the mortality and lipid deposition in the high-fat diet fed rice field eel. • Taurine enhanced the antioxidant capacity and intestinal health in the high-fat diet fed rice field eel. [ABSTRACT FROM AUTHOR]

An eight-week feeding trial was performed to determine how methionine regulates muscle growth in the rice field eel Monopterus albus (initial weight 25.08 ± 0.31 g). Six isonitrogenous and isoenergetic experimental feeds were formulated, and different levels of methionine (0, 2 g/kg, 4 g/kg, 6 g/kg, 8 g/kg, or 10 g/kg) were added to the basic diet (110 g/kg fish meal, 400 g/kg soy concentrate meal). The weight gain rate (WGR) of M. albus markedly increased as methionine concentrations increased to 6 g/kg (P < 0.05) and gradually decreased as methionine concentrations increased to 10 g/kg. The feed conversion rate of M. albus showed a trend opposite to the WGR. Muscle glycogen markedly increased as methionine concentrations increased to 2 g/kg (P < 0.05), while the creatine kinase, lactic acid and lactate dehydrogenase contents of muscle markedly decreased as dietary methionine concentrations increased to 2 g/kg (P < 0.05). The content of amino acids, total essential amino acids, total nonessential amino acids and total amino acids in muscle was increased by supplementation with 8 g/kg and 10 g/kg methionine. The springiness of muscle markedly increased as methionine supplementation increased to concentrations of 6 g/kg (P < 0.05). The hardness, gumminess and chewiness of muscle markedly increased as methionine concentrations increased to 8 g/kg (P < 0.05). When supplemented with 8 g/kg and 10 g/kg methionine, the density of muscle fibers and the percentage of muscle fibers under 60 μm were remarkably decreased, while the percentage of muscle fibers greater than or equal to 100 μm was remarkably increased (P < 0.05). When 8 g/kg and 10 g/kg methionine were added, gcn2 and mstn mRNA expression was significantly downregulated (P < 0.05), while gh , ghr , TnT , mhc , mlc , myf5 , myod2 , myog , pax7 and mef2a mRNA expression was remarkably upregulated (P < 0.05). Correlative analysis of muscle-related gene expression showed that myf5 , mlc , and myog expression was negatively correlated with gcn2 expression (P < 0.05), and ghr , mef2b , gh , and mhc expression was negatively correlated with gcn2 expression (P < 0.01), while mstn expression was positively correlated with gcn2 expression (P < 0.01). In conclusion, dietary methionine increased the growth performance of M. albus , especially for muscle growth and development, improved muscle texture and main nutritional factors (amino acids, glycogen), and reduced the content of lactic acid in muscle. • Dietary methionine enhanced muscle growth by increasing diameters of muscle fibers. • Dietary methionine improved muscle texture, amino acids and glycogen of muscle. • gcn2 gene could be activated when M. albus feed intake methionine deficiency diet. [ABSTRACT FROM AUTHOR]

Asian swamp eel (Monopterus albus), an economically important fish species in China and other Asian countries, is susceptible to Aeromonas hydrophila infection. A deeper understanding of the Asian swamp eel immune system and its genes related to the response to bacterial infection is necessary for disease control in this species. Herein, we analysed the transcriptomic profile of spleen from Asian swamp eel challenged with A. hydrophila by using the Illumina-based paired-end sequencing method. More than 99.39% clean reads were successfully mapped to the reference genome of M. albus , including 1501 differentially expressed genes (DEGs), of which 928 were upregulated and 573 were downregulated. Additionally, 5911 terms were enriched in Gene Ontology (GO) analysis, and 284 pathways were identified in Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis. The reliability of the transcriptome data was validated by quantitative PCR (qPCR). Enrichment analysis of DEGs identified major immune-related pathways, including Toll-like receptor, complement and coagulation cascades, and T- and B-cell receptor signalling pathways. Our results provide valuable information for further analysis of the mechanisms underpinning M. albus defences against A. hydrophila. • This report described the change on inflammation-related genes of Asian swamp eel following infection with Aeromonas hydrophila. • Immune genes, such as complement, interleukin, tumor necrosis factor receptor and so on, was modulated after Asian swamp eel infection with Aeromonas hydrophila. • Our data suggested that many immune genes might play a significant role in the immune response of Asian swamp eel after infection with Aeromonas hydrophila. [ABSTRACT FROM AUTHOR]

Hematology can provide valuable information for the evaluation of fish health. Rice field eel (Monopterus albus), a typical protogynous hermaphrodite fish, is famous for a fairly high nutritive value as a popular farmed fish in some Asian country, especially in China. Basic characteristics and reference values of hematology is poorly understood in M. albus , which hinder disease prevention and breeding in aquaculture. In this study, cell types, changes and typical parameters of peripheral blood were identified and systematically analyzed in M. albus during natural sex reversal. Erythrocytes, leukocytes and thrombocytes were distinguished, meanwhile, their cellular and ultrastructural features were analyzed among female, intersex and male individuals. The number and area of erythrocyte in males was significantly higher than that in both females and intersex. After detecting the serum estradiol and 11-keto testosterone level, changes of erythrocyte are the same as the trends among female, intersex and male in 11-keto testosterone level. Interestingly, dividing erythrocyte was found in the peripheral blood among the three types individuals, more dividing erythrocytes were found in intersex. The differential leukocyte count (DLC) revealed predominance of lymphocytes, followed by neutrophils and monocytes, and showed significant differences among female, intersex and male. Our findings revealed the types, cellular and ultrastructural features, and dynamic changes of blood cell during sex reversal in M. albus. It provides hematological reference for breeding, disease prevention and control in protogynous hermaphrodite fish, especially M. albus. • Reference values of growth performance, sex hormones level and hematological parameters were established in M. albus. • Dynamic changes of erythrocytes, leukocytes and thrombocytes were described during nature sex reversal. • Dividing erythrocyte was found in M. albus , it was frequently observed in intersex individuals. [ABSTRACT FROM AUTHOR]

An eight-week feeding trial was conducted to evaluate the effects of soy isoflavone and soy saponin on growth performance, intestinal structure, intestinal immunity and gut microbiota community of rice field eel Monopterus albus (initial weight 20.12 ± 0.15 g). Six isonitrogenous and isolipidic experimental feeds were formulated, including a positive control (55% fish meal, FM), a negative control (28.6% fish meal, 37.2% soybean meal, SBM) and basic diet group (28.6% fish meal, 22.6% soy protein concentrate, SPC), the rest was supplemented with soy isoflavone (40%, 2.5 g / kg, SI), soy saponin (≥98%, 2 g / kg, SS) and their mixed in basic diet (SI + SS). Compared with FM, growth performance, intestinal immune indices (acid phosphatase, alkaline phosphatase, complement 3, complement 4 and immunoglobulin M), intestinal villus height and intestinal muscular thickness and mRNA (occludin-like, claudin 12, tight junction protein ZO-1-like, tight junction protein ZO-2-like, interleukin-10, transforming growth factor beta 1, transforming growth factor beta 2) expression intestine of M. albus fed SBM diet were significantly decreased (P < 0.05). Growth performance of M. albus in SPC group was better than that in SBM. Compared with SPC, dietary soy isoflavone and soy saponin and their mixed (SI, SS, SI + SS) decreased growth of M. albus , serum alkaline phosphatase in SI significantly increased (P < 0.05), and intestinal immunoglobulin M in SS remarkably declined (P < 0.05), intestinal complement 3, complement 4 and immunoglobulin M, amounts of intestinal goblet cells per root, gut shannon were significantly decreased in SI + SS (P < 0.05). Based on the current results, there has the trend that dietary soy isoflavone and soy saponin damaged the intestinal structure and changed gut bacteria community of M. albus , and destroyed the intestinal barrier, eventually induced intestinal inflammatory, soy isoflavone and soy saponin mixed feed has more serious effects than they single supplemented. • Dietary soy isoflavone, soy saponin and their mixed feed decreased the growth performance of M. albus. • Soy isoflavone and soy saponin damaged intestinal structure and intestinal barrier, induced intestinal inflammatory. • Dietary soy isoflavone and soy saponin mixed feed has more serious effect than they single supplemented. [ABSTRACT FROM AUTHOR]

An eight-week feeding trial was conducted using sulfur amino acids to overcome methionine deficient diets on rice field eel Monopterus albus (initial weight 25.12 ± 0.51 g). Six isonitrogenous and isoenergetic experimental formulations included 55% fish meal group (FM, a reference), 22% fish meal group (D 0), and the rest four diets (22% fish meal) supplemented with 2 g/kg of taurine (D Tau), methionine (D Met), cysteamine hydrochloride (D Csh) and cystine (D Cys), respectively. Compared with FM, the growth performance of M. albus was markedly declined in D 0 (P < 0.05); while the growth performance of M. albus in D Met , D Csh and D Cys were remarkably higher than D 0 (P < 0.05), and these groups were indifference with FM (P > 0.05). Compared with FM, the highest amount of hepatic vacuoles was observed in D 0 , while the proportions of vacuoles were lower in D Met , D Csh and D Cys groups than that in D 0 , dietary sulfur amino acids also have improved hepatic transaminase and the ability of amino acid metabolism. Compared with FM, muscular texture, density and diameters of muscle fibres were significantly decreased in D 0 (P < 0.05); while muscular texture were significantly increased in D Csh and D Cys (P < 0.05). Compared with D 0 , dietary sulfur amino acids improved diameters of the muscle fibres. Myocyte myogenic regulatory (Mrf4, MyoD2, Myog and Mrf4) and myocyte enhancer factors (MEF2b and MEF2c) mRNA expression in D 0 were markedly lower than that in FM (P < 0.05), compared with D 0 , the expression of Mrf4 and MEF2b in D Met were significantly up regulated (P < 0.05); the expressions of Mrf4, MyoD2 and MEF2b in D Csh were markedly higher than that in D 0 (P < 0.05), MyoD2, Myog, MEF2b and MEF2c in D Cys also were remarkably higher than that in D 0 (P < 0.05). Overall, our study indicated that dietary methionine, taurine, cysteamine hydrochloride and cystine in low fish meal diet could improve amino acids metabolism and muscle growth for M. albus , moreover, cysteamine hydrochloride and cystine overcame methionine deprivation partly. • Methionine deficiency decreased growth of M. albus , affected hepatic amino acids metabolism, decreased muscle growth. • Dietary taurine, cysteamine hydrochloride and cystine in methionine deficiency diet improved muscle growth of M. albus. • Cysteine and cysteamine overcame negative impact by a certain level of methionine deficiency successfully. [ABSTRACT FROM AUTHOR]

The rice field eel, Monopterus albus , is an important freshwater fish cultured in China. In this study, mitotic gynogenesis was induced in the rice field eel using heat shock (40.5 ± 0.5 °C for 3.5 min) on eggs activated by ultraviolet (UV) - irradiated sperm of common carp (Cyprinus carpio). Initially, the first embryonic cell cycle was identified using histological analysis. The optimal initiation time for heat shock treatment was then determined by analyzing both the diploid and normal hatching rates. Ploidy was confirmed using flow cytometry and karyotype analyses. Embryos began to enter prophase at 70 mpf (min post-fertilization) and the first cleavage was completed at 125 mpf. Both haploid and hybrid embryos died before hatching. Heat shock treatment before metaphase (75 mpf) and at telophase (100 mpf) can induce chromosome doubling and produce viable individuals. For eggs treated before metaphase, heat shock treatment at 60 mpf, corresponding to the stage of pronuclear fusion, had the highest diploid rate (33.26 ± 4.4%) and normal hatching rate (3.94 ± 0.12%). For eggs treated at telophase (100 mpf), the diploid rate was 100% and the highest normal hatching rate was 26.77%. Therefore, the optimal time to apply heat shock treatment to induce mitotic gynogenesis in the rice field eel was at telophase during the first mitosis process. This technology could potentially accelerate the development of a new breed of rice field eel. • Mitotic gynogenesis in M. albus was induced by heat shocking eggs activated by common carp sperm. • The first cell cycle in early embryogenesis stage of M. albus was identified. • Whole genome doubling by heat shock is optimum at telophase of the first cleavage. • This mitotic gynogenesis induction method is useful in the breeding of M. albus. [ABSTRACT FROM AUTHOR]