Search

The ricefield eel (Monopterus albus), a protogynous hermaphroditic Synbranchiform species, is one of the most economically valuable freshwater fish in China. Studies on the sexual change of the ricefield eel will contribute to artificial culture and understanding the sex determination and differentiation in fish. In this study, the whole‐genome DNA methylation and transcriptomes of ovary and testis were analysed in ricefield eel. An elevated methylation level in the genome was observed in the testis compared with the ovary. A total of 457 genes showed a negative correlation between DNA methylation status and expression level in the testis compared with the ovary. Of these genes, 16 candidates were screened on the basis of their vital roles reported in gonadal development. The methylation statuses and expression levels of dnmt3a, piwil1, tdrd1, sox30, nanos2, socs2, mei4 and zmiz1 were further validated using bisulphite sequencing PCR and quantitative real‐time PCR respectively. These potential vital genes would be useful for future studies on the molecular mechanism of sex reversal in ricefield eel. Besides, the integrated analysis of DNA methylation and expression level of gonads provides basic information for epigenetic regulation in the process of sexual reversal in ricefield eel. [ABSTRACT FROM AUTHOR]

An 8‐week trial investigated how andrographolide effected lipopolysaccharide (LPS)‐induced serum biochemical indices, immune responses and the intestinal inflammatory response of Monopterus albus. The study included control and andrographolide groups (150 mg/kg andrographolide) with three replicates per group. Samples were taken 0, 3, 6, 12, 24 and 48 h after LPS injection. The results showed that the levels of GLU, COR, AST, ALT, IgM, LZM, AKP, C3 and C4 in serum showed an initial increasing that then decreased. Compared with that of the control group, the levels of serum LZM, AKP, IgM, C3 and C4 in the andrographolide group increased quicker after LPS injection, while the levels of GLU, COR, AST and ALT increased more slowly; further, these indices recovered to normal levels quicker. The expression of several genes in the intestine first increased and then decreased after LPS injection. Compared with that of the control group, il‐10, tgf‐β1, tgf‐β2 and tgf‐β3 gene expression in the andrographolide group increased quicker after LPS injection, while that of il‐1β, il‐8, il‐12β, nf‐κb, tlr‐3, tlr‐7 and tlr‐8 increased more slowly; these indices recovered to normal levels more quickly. In conclusion, LPS injection induced immune stress and inflammatory response in M. albus. Dietary supplementation with 150 mg/kg andrographolide effectively alleviated these responses. [ABSTRACT FROM AUTHOR]

Three experimental diets including frozen trash fish (Diet 1), the equal mixture of frozen trash fish and formulated pellets (Diet 2), and formulated pellets (Diet 3) were prepared and fed to the female broodstocks of Monopterus albus for 6 weeks. Swamp eels fed with Diet 3 exhibited lower values of weight gain and specific growth rate (p < 0.05). Plasma concentrations of total protein, total cholesterol and estradiol were higher in fish fed Diet 1. Fish fed with Diet 3 had higher values of crude protein (CP) and ash, together with lower moisture concentration in muscle. Concentrations tendency of CP, ash and moisture in the ovary were completely opposite to that in the muscle. The concentration of total n−3 fatty acids was highest in both the muscle and ovary of fish fed Diet 1. Fertilization of eggs in fish fed Diet 3 was blocked. It suggested that the insufficiency of plasma estradiol, and n−3 fatty acids in the muscle and ovary, together with the impediment of protein mobilization from muscle to ovary, caused the fertilization failure of M. albus fed with formulated feeds. Equal mixture of trash fish and formulated pellets was appropriate for the successful propagation of swamp eels. [ABSTRACT FROM AUTHOR]

Five isonitrogenous and isocaloric diets containing dietary lipid concentrations from 71.90 to 142.70 g/kg were formulated and fed to Chinese rice field eel Monopterus albus fingerlings (5.00 ± 0.50 g). The highest values of weight gain, specific growth rate (SGR), together with the lowest feed conversion ratio (FCR) were found in fish fed with 89.10 g/kg lipid diet. Fish fed with 71.90 g/kg diet (F1) had higher hepatosomatic index, viscerosomatic index and whole‐body crude lipid than fish in the other four treatments (p <.05). Plasma concentration of triacylglycerol and the activity of alanine aminotransferase were also higher in fish fed with F1 diet. Whole‐body fatty acid profile varied exclusively, but with a stable value of n−3/n−6 ratio. Gas chromatography–mass spectrometry‐based metabolomics identified eighteen differential metabolites (including idose, alanine, glutamic acid, serine and hypotaurine) in liver affected by dietary lipid content using PLS‐DA analysis. The subsequent pathway enrichment revealed ten affected pathways, with the top three pathways being glycine, serine and threonine metabolism; starch and sucrose metabolism; and D‐glutamine and D‐glutamate metabolism. The broken‐line model of SGR suggested that a dietary lipid concentration of 83.50 g/kg was appropriate for M. albus fingerlings. [ABSTRACT FROM AUTHOR]

Swamp eel or rice field eel (Monopterus albus) is one of the most economically valuable freshwater fishes in China. Based on the body colour patterns, Chinese rice field eels are commonly classified into three strains, including deep‐yellow strain (DY), pale‐yellow strain (PY) and steel‐grey strain (SG). Reports have shown that DY strain is superior to the other two strains at growth rate and fecundity. In the present study, RNA‐Seq technology was employed to profile liver transcriptomes of these three strains, and differentially expressed genes (DEGs) were identified. The hierarchical clustering analysis showed that expression patterns of liver transcripts among the three strains were different. A total of 3,296 DEGs, 3,043 DEGs and 143 DEGs were identified, respectively, from DY versus SG, DY versus PY and PY versus SG. The three comparison groups shared three DEGs, of which one DEG (batf) played a vital role in immune system. Functional enrichment analyses of DEGs in DY versus PY and DY versus SG revealed that significantly enriched Gene Ontology terms and KEGG pathways were mainly involved in innate immune responses and lipid metabolism. Additionally, most of DEGs related to immunity were mainly up‐regulated in DY compared to PY and SG. The above results indicated that the DY strain might have strong adaptability and resistance to disease, which might support their superiority for better growth and reproduction. [ABSTRACT FROM AUTHOR]

At present, research into the impact of microplastic contamination on environmental and food safety in the eel farming industry is insufficient. Here, we investigated the occurrence of microplastics in eels (Monopterus albus), wastewater and soils from recycled‐water, cement‐pool, net‐cage and rice‐field rearing systems. Results showed that average microplastic abundances were 2.4 ± 0.8 items/individual, 1.0 ± 0.4 items/L, 27.1 ± 7.0 items/kg in eels, water and soils, respectively. A significant increase in microplastic abundances occurred in all diet‐fed eels (recycled‐water, cement‐pool and net‐cage eels) from their pre‐rearing to post‐rearing stages. Moreover, cluster analysis indicated high similarities in composition of microplastics between fish diets and eels. However, no significant differences in microplastic abundances were observed among the four types of reared eels. Most of the microplastics were found in the foreguts of eels. In addition, wastewater microplastic increased significantly in the cement‐pool, net‐cage and rice‐field farming during eel rearing. This study first revealed microplastic contamination and its characteristics in eels‐rearing environments, which suggests the eco‐environmental risk of microplastics in aquaculture. [ABSTRACT FROM AUTHOR]

Housefly larvae are widely used in livestock breeding industry as a functional feed additive with immunostimulant properties, but their effects as dietary additive are poorly understood in aquatic animals. We conducted an eight‐week rearing experiment to determine the effects of housefly larvae (complete) on growth performance, immunity and intestinal microbiota in swamp eel (Monopterus albus). Dietary treatments were as follows: BD (control group, fed a basal diet), FL7 (fly larvae supplemented once weekly, i.e., 6‐day basal diet, 1‐day larvae) and FL3 (larvae supplemented every third day, i.e., 2‐day basal diet, 1‐day larvae). The final body weight (FBW) and weight gain (WG) of the FL3 group significantly (p <.05) increased. Hepatosomatic index (HSI) and malondialdehyde (MDA) concentration significantly decreased in FL3 and FL7 groups. The expression of immune‐related genes was also influenced by the fly larvae. Aeromonas hydrophila challenge experiment produced higher survival rates in the FL3 (75%) and FL7 (37.5%) groups. Fly larvae also affected the composition of gut microbiota: the abundance of Bacteroides increased, and Pseudomonas decreased, in the treatment groups. Dietary supplementation of housefly larvae has positive effects on the growth and immunity of swamp eel, and we suggest supplementing housefly larvae every third day. [ABSTRACT FROM AUTHOR]

A 12‐week feeding trial was conducted to determine the influence of dietary protein levels on growth performance, body composition, haematological parameters and digestive enzyme activity of Chinese rice field eel (Monopterus albus) fingerlings. Six isolipidic experimental diets (27.89%, 32.23%, 35.95%, 40.06%, 43.31% and 46.53%) were formulated to randomly assign to triplicate groups of 50 rice field eel fingerlings (5.0 ± 0.5 g) cultured in plastic cages. Results indicated that the best growth performance of fish with the highest WG (158.68 ± 31.59%) and SGR (2.28 ± 0.21%) was obtained at 40.06% group. Significant alterations were demonstrated on whole‐body crude protein, crude lipid and amino acid profile by different dietary protein levels. Besides, haematological parameters including triacylglycerol, aspartate aminotransferase and alkaline phosphatase decreased with various levels by the increasing of dietary protein levels. The lowest pepsin activity was observed in 27.89% protein group, which suggested lower availability of protein as substrate for protease activity. Meanwhile, the highest amylase activity in fish of 27.89% group indicated higher carbohydrate level in this group. Based on the polynomial regression analysis of WG and SGR, the dietary protein requirement for fingerlings of Monopterus albus was estimated to be 386.4–390.8 g/kg, respectively, with the lipid level of 10.08%. [ABSTRACT FROM AUTHOR]

More and more diseases were occurred in the aquaculture of Asian swamp eel. Bacterial isolates were collected from the pathogenic organs of diseased Asian swamp eels. A dominant strain, Aeromonas veronii JL‐01, was isolated and identified from the liver and intestine tissue of diseased Asian swamp eels. The symptoms of fish infected artificially with A. veronii were the same as those observed under natural infection. The mortality rate was 40%–80% and infected Asian swamp eels died 2–3 days after infection. Drug sensitivity tests showed that the isolated bacterium was highly sensitive to seven kinds of antibiotics, including cephalosporins, aminoglycoside, quinolones, tetracyclines (except Tetracycline), pheniclos, nitrofurans and sulfonamides. The bacterium was resistant to penicillins (except Piperacillin), macrolides, polypeptides and lincomycin. The histological changes in Asian Swamp Eel induced by A. veronii infection mainly occurred in the liver, intestines and kidney. A. veronii showed strong pathogenicity towards the Asian swamp eel, causing tissue damage and death. Gentamycin, doxycycline and sulfamethoxazole could be used for preventing and treat this disease. [ABSTRACT FROM AUTHOR]

Abstract: This study was conducted to evaluate the effect of dietary taurine supplementation on growth, immunity and resistant to dry stress of rice field eel (Monopterus albus) fed low fish meal diets. Six isonitrogenous and isolipid diets (32% fish meal) supplemented with six taurine concentrations (0, 0.3, 0.6, 0.9, 1.2 and 1.5 g/kg; designated as T0, T0.03, T0.06, T0.09, T0.12 and T0.15 groups, respectively) were prepared. A diet including 42% fish meal (FM group) was also included as a reference. The results showed that specific growth rate (SGR) in FM group was significantly higher than that in lower fish meal treatments. SGR significantly increased and slowly decreased with the increase in taurine supplementation level. Lipase activity value in intestine of M. albus fed FM diet was maximum, and with the increase in taurine supplementation level, lipase activity significantly increased and slowly decreased. The FM group had relative higher total antioxidant capacity (T‐AOC) content, catalase (CAT), total superoxide dismutase (T‐SOD), and lyzozyme (LZM) activities in serum than the other groups. With the increase in dietary taurine supplementation level, the CAT, T‐SOD, T‐AOC and LZM activities in serum significantly increased and then decreased. In the dry stress experience, the adrenaline (AD), cortisol (COR), glucose (GLU), total cholesterol (CHOL), and malondialdehyde (MDA) concentrations, T‐AOC content, CAT and T‐SOD activities in serum of M. albus in the four groups first increased and reached the peak at 2 hr, and then decreased under air‐exposure stress. Compared to the FM group, T0.15 group had relative higher T‐AOC content, CAT and T‐SOD activities, and lower AD, COR GLU, TC and MDA concentrations. [ABSTRACT FROM AUTHOR]

The article reports on the isolation and characterization of the Edwardsiella tarda from diseased Asian swamp eel known as Monopterus albus (Zuiew). Edwardsiella tarda is the causative agent of edwardsiellosis and has caused significant losses in many marine fish species throughout the world. The commercial importance of Asian swamp eel is also discussed.

The Asian swamp eel Monopterus albus is normally considered a freshwater species, but can also occasionally be found in brackish water. It is an obligate air-breather with highly reduced gills, making its osmoregulation physiology interesting because the gills normally represent the primary site of osmoregulation in teleosts. Being a popular fish for human consumption, the swamp eel is cultured extensively in freshwater ponds in the Mekong Delta of Vietnam. However, very little is known about its salinity tolerance, which is becoming topical due to the increasing salt-water intrusions into tropical deltas. We therefore studied how increased salinity affects survival, growth, blood pressure, heart rate, blood osmolality and plasma ions. All eels survived prolonged exposure to 5 and 10 g L−1, although plasma osmolality increased significantly at 10 g L−1. Further elevation to 15 and 20 g L−1 was associated with significantly elevated mortality, with a corresponding increase in plasma osmolality and ion con-centrations. Our results show that swamp eels thrive in 0-10 g L−1 with an optimum growth between 0 and 9 g L−1, indicating that utilization of low saline brackish waters for aquaculture is possible. [ABSTRACT FROM AUTHOR]

Phylogenetic inference of mitochondrial control region (501 bp) of 167 individuals from 12 regional populations revealed that Chinese swamp eels fell into five genetic lineages, Lineage A, B, C, D and E. Lineage A was speculated to share the same mitochondrial ancestors with the populations from Taiwan Island. Lineage C harboured most of the haplotypes (39/60) of populations and may have experienced population expansion. The distribution pattern of Lineage C from east to west regions may have resulted from the occurrence of the major glaciation and inter-regional introduction. Lineage A, B and E inhabiting coastline regions were immune from the expansion of Lineage C due to isolation from inland areas blocking gene flow between inland and coastal populations. On the other hand, Chinese swamp eels were revealed to be maintaining substantially differentiated population structures, while three populations from the Sichuan basin ( MY, LC and YA) were genetically closely related. This was attributed to the geographical isolation of Sichuan populations from other populations, facilitating gene flow among the three populations from the Sichuan basin. [ABSTRACT FROM AUTHOR]