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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]

Aeromonas hydrophila causes sepsis and is responsible for significant economic losses in Asian finless eel (Monopterus albus) aquaculture. Previous studies have found that macrophage migration inhibitory factor (MIF) and Cathepsin B (CTSB) may be expressed in many vertebrate tissues and organs. However, there have been no reports discussing the importance of MIF and CTSB in Asian swamp eel. The complete ORF sequences of MAMIF and MACTSB were found to be 348 and 993 bp, respectively. The adaptive analysis showed that the sequences of MAMIF and MACTSB were highly conserved, and only two positive selection sites were identified in MAMIF. Quantitative real time polymerase chain reaction (qRT‐PCR) demonstrated that MAMIF and MACTSB genes were expressed in all tissues evaluated with the highest expression occurring in the head kidney, spleen and liver. Challenge with Aeromonas hydrophila resulted in a significant increase in the expression of MAMIF and MACTSB in skin, liver, head kidney and spleen that peaked at 12‐h post‐infection. The results show that MAMIF and MACTSB play important roles in the immune function of Monopterus albus. [ABSTRACT FROM AUTHOR]

A 10‐week feeding trial aimed to investigate the effects of dietary vitamin C (l‐ascorbic acid) on growth, antioxidant activity, and immunity in ricefield eel, Monopterus albus. Six diets were formulated with different levels of vitamin C supplementation (0.1, 17.5, 34.8, 68.6, 139.7, and 278.5 mg/kg). The results indicated that the weight gain (WG) of the M. albus fed the diets with vitamin C was remarkably higher than that of the M. albus fed the control diet (p <.05), and the quadratic analysis showed an optimal vitamin C level of 80.66 mg/kg. Compared with the control group, serum lysozyme activities, the complement pathway, red blood cell counts, white blood cell counts, immunoglobulin M, and phagocytosis percentage were significantly increased (p <.05) in the treatment groups, and superoxide dismutase activity, serum glucose, and malondialdehyde content were significantly decreased (p <.05) in the treatment groups. The challenge trial with Aeromonas hydrophila showed that the M. albus fed the diets with vitamin C had remarkably reduced cumulative mortality compared with those fed the control diet (p <.05), and mortality in the 68.60 mg/kg diet group was the lowest. Based on WG, the optimal vitamin C supplementation level for M. albus was estimated to be 80.66 mg/kg. [ABSTRACT FROM AUTHOR]

Abstract: The myocyte‐specific enhancer factor 2 (MEF2) gene family members are well‐established regulators in the control of muscle repair, regeneration, and development. In this study, we cloned the CDS sequences of the four MEF2 family members in the ricefield eel, and their coding sequences (CDS) lengths were 1449 bp, 1419 bp, 1431 bp, and 1608 bp, respectively. Sequence analysis demonstrated that three of them shared four conserved protein domains, including a MADS‐Box, inside SRF‐TF domains, adjacent conserved MEF2 domains, the HJURP‐C domains, while MEF2B have no HJURP‐C domains. Phylogenetic tree analyses indicated that the MEF2 family members were clustered together with those of fish species, and MEF2A, MEF2C, and MEF2D were closely clustered together and kept away from MEF2B. Spatial–temporal expression profiles displayed that the messenger RNA (mRNA) levels of MEF2 were upregulated with the developmental stage and were especially highly expressed significantly in skeletal muscles. After subcutaneous injection of bupivacaine hydrochloride, mRNA levels of MEF2 family and rapidly performed injury‐responsive regulation after damage that firstly increased, then decreased until normal levels were recovered, the same as the change in muscle fiber cells. In conclusion, the MEF2 gene family plays a central role in muscle repair, regeneration, and development in fish, at least in the ricefield eel. [ABSTRACT FROM AUTHOR]

This study investigated the hypothesis that in the Asian swamp eel Monopterus albus, an air-breathing fish from south-east Asia that uses the buccopharyngeal cavity for oxygen uptake, the upper critical temperature ( TU) is increased by acclimation to higher temperature, and that the increased TU is associated with improved cardiovascular and respiratory function. Monopterus albus were therefore acclimated to 27° C (current average) and 32° C (current maximum temperature as well as projected average within 100-200 years), and both the effect of acclimation and acute temperature increments on cardiovascular and respiratory functions were investigated. Two weeks of heat acclimation increased upper tolerated temperature ( TU) by 2° C from 36·9 ± 0·1° C to 38·9 ± 0·1° C (mean ± s.e.). Oxygen uptake ( [ABSTRACT FROM AUTHOR]

The ovarian differentiation, morphogenesis and expression of some putative gonadal development-related genes were analysed in the ricefield eel Monopterus albus, a protogynous hermaphroditic teleost with a single elongate ovary. At c. 1 day post-hatching (dph), the gonadal ridge was colonized with primordial germ cells ( PGCs) at the periphery and transformed into the gonadal primordium, which appeared to contain two germinal epithelia. At c. 7 dph, four ovarian cavities appeared in the gonadal tissue with two in each germinal epithelial compartment, and the indifferent gonad might have begun to differentiate into the ovary. The oocytes at the leptotene stage in meiosis I appeared at c. 14 dph, and oocytes at the diplotene stage at c. 30 dph. As development proceeded, the connective tissue separating the two germinal epithelia disappeared, and two of the four ovarian cavities collapsed into one. At 60 dph, the gonad had already taken the shape as observed in the adults. One outer and two inner ovarian cavities could be easily recognized, with slightly basophilic primary growth oocytes usually residing close to the outer ovarian cavity. The expression of cyp19a1a and erb in the early gonad was detected at 6 dph. The abundant expression of foxl2 coincided with the up-regulation of cyp19a1a at 8 dph onwards. The expression of dmrt1 isoforms was not detectable until 8 dph for dmrt1a and dmrt1b and until 33 dph for dmrt1d. The earlier appearance of cyp19a1a compared to dmrt1 transcripts in the indifferent gonad may contribute to the initial differentiation of the gonad towards the ovary in M. albus. [ABSTRACT FROM AUTHOR]

The rice field eel ( Monopterus albus) is a fish of economic importance in China and some Asian countries. From a (GT) n-enriched genomic library, 30 microsatellites were developed by employing the fast isolation by AFLP of sequences containing repeats (FIASCO) protocol. Thirteen loci exhibited polymorphism with two to 13 alleles (mean 7.9 alleles/locus) in a test population and observed heterozygosity ranged from 0.3125 to 0.9688 (mean 0.7140). These loci should provide sufficient level of genetic variation to study the fine-scale population structure and reproductive ecology of the species. [ABSTRACT FROM AUTHOR]

A personal narrative is presented in which the author talks about the time when he first held an Asian swamp eel or Monopterus albus, stating that they live in muddy burrows and are not easy to see even though they are slithering enough.