Autonomic control of the heart in the Asian swamp eel (Monopterus albus)

The Asian swamp eel (Monopterus albus) is an air-breathing teleost with very reduced gills that uses the buccal cavity for air-breathing. Here we characterise the cardiovascular changes associated with the intermittent breathing pattern in M. albus and we study the autonomic control of the heart during water- and air-breathing. The shift from water- to air-breathing was associated with a rise in heart rate from 27.7 ± 1.6 to 41.4 ± 2.6 min(-1) and an increase in cardiac output from 23.1 ± 3.0 to 58.7 ± 6.5 mLmin(-1)kg(-1), while mean systemic blood pressure did not change (39.0 ± 3.5 and 46.4 ± 1.3 cmH(2)O). The autonomic control of the heart during water- and air-breathing was revealed by infusion of the β-adrenergic antagonist propranolol and muscarinic antagonist atropine (3 mgkg(-1)) in eels instrumented with an arterial catheter. Inhibition of the sympathetic and parasympathetic innervations of the heart revealed a strong vagal tone on the heart of water-breathing eels and that the tachycardia during air-breathing is primarily mediated by withdrawal of cholinergic tone.     

Structure of the air-breathing organs of a swamp mud eel,Monopterus cuchia

The structure of the air-breathing organs ofMonopterus (=Amphipnous)cuchia has been studied by using light, scanning and transmission electron microscopy and the morphological basis for buccopharyngeal respiration, aerial as well as aquatic has been established. Respiratory islets are well distributed over the surface of the buccopharynx, hypopharynx and branchial arches extending deep into the gill clefts but occupy only the anterior two-thirds of the air sacs, the remaining posterior one-third part seems to be non-respiratory in function and may serve as a reservoir for residual air. Arterioles penetrate deep into the epithelial region of air sacs and buccopharynx in spiral-like fashion to form the characteristic vascular papillae of the respiratory islets. In juvenile fish new respiratory islets develop in the non-vascular part of the air sac in between large older islets as sprout-like structures. The respiratory area, capillary loading, thickness of air-blood tissue barrier, and the diffusing capacity of the respiratory membrane of a 200 g fish were found to be 20 cm², 2.72 cm³/m², 0.72 × 10^?4 cm, and 0.00165 ml O₂/min/mmHg/kg, respectively.     

Identification of Dmrt genes and their up-regulation during gonad transformation in the swamp eel (Monopterus albus)

The swamp eel is a teleost fish with a characteristic of natural sex reversal and an ideal model for vertebrate sexual development. However, underlying molecular mechanisms are poorly understood. We report the identification of five DM (doublesex and mab-3) domain genes in the swamp eel that include Dmrt2, Dmrt2b, Dmrt3, Dmrt4 and Dmrt5, which encode putative proteins of 527, 373, 471, 420 and 448 amino acids, respectively. Phylogenetic tree showed that these genes are clustered into corresponding branches of the DM genes in vertebrates. Southern blot analysis indicated that the Dmrt1–Dmrt3–Dmrt2 genes are tightly linked in a conserved gene cluster. Notably, these Dmrt genes are up-regulated during gonad transformation. Furthermore, mRNA in situ hybridisation showed that Dmrt2, Dmrt3, Dmrt4 and Dmrt5 are expressed in developing germ cells. These results are evidence that the DM genes are involved in sexual differentiation in the swamp eel.     

Strategies for surviving high concentrations of environmental ammonia in the swamp eel Monopterus albus

The swamp eel Monopterus albus lives in muddy ponds, swamps, canals, and rice fields in the tropics. It encounters high concentrations of environmental ammonia (HEA) during dry seasons or during agricultural fertilization in rice fields. This study aimed at determining the tolerance of M. albus to environmental ammonia and at elucidating the strategies that it adopts to defend against ammonia toxicity in HEA. In the laboratory, M. albus exhibited very high environmental ammonia tolerance; the 48-, 72-, and 96-h median lethal concentrations of total ammonia at pH 7.0 and 28 degrees C were 209.9, 198.7, and 193.2 mM, respectively. It was apparently incapable of actively excreting ammonia against a concentration gradient. In addition, it did not detoxify ammonia to urea, the excretion of which would lead to a loss of nitrogen and carbon, during ammonia loading. The high tolerance of M. albus to HEA was attributable partially to its exceptionally high tolerance to ammonia at the cellular and subcellular levels. During the 144 h of exposure to 75 mM NH(4)Cl at pH 7.0, the ammonia contents in the muscle, liver, brain, and gut of M. albus reached 11.49, 15.18, 6.48, and 7.51 mu mol g(-1), respectively. Such a capability allowed the accumulation of high concentrations of ammonia in the plasma (3.54 mu mol mL(-1)) of M. albus exposed to HEA, which would reduce the net influx of exogenous ammonia. Subsequent to the buildup of internal ammonia levels, M. albus detoxified ammonia produced endogenously to glutamine. The glutamine contents in the muscle and liver reached 10.84 and 17.06 mu mol g(-1), respectively, after 144 h of exposure to HEA, which happened to be the highest known for fish. Unlike urea, the storage of glutamine in the muscle during ammonia loading allowed its usage for anabolic purposes when the adverse environmental condition subsides. Glutamine synthetase activity increased significantly in the liver and gut (2.8- and 1.5-fold, respectively) of specimens exposed to HEA for 144 h. These results suggest that the liver was the main site of ammonia detoxification and the gut was more than a digestive/absorptive organ in M. albus. Monopterus albus did not undergo a reduction in amino acid catabolism during the first 24 h of ammonia exposure. However, assuming a total inhibition of excretion of endogenous ammonia, there was a deficit of -312 mu mol N between the reduction in nitrogenous excretion (3,360 mu mol N) and the retention of nitrogen (3,048 mu mol N) after 72 h of aerial exposure. The deficit became much greater after 144 h, reaching a value of -3,243 mu mol N. These results suggest that endogenous ammonia production in M. albus was suppressed in order to prevent the newly established internal steady state concentration of ammonia from rising to an intolerable level after an extended period of exposure to HEA.     

Genetic diversity of wild and cultured swamp eel (Monopterus albus) populations from central China revealed by ISSR markers

Asian swamp eel is a highly commercial fish, primarily for China and other Asian countries. The aim of this paper is to evaluate the genetic diversity of wild and cultured samples of Asian swamp eel Monopterus albus using ISSR markers. A total of 129 individuals belonging to three wild samples, Xiantao (XT), Huanggang (HG), Xinyang (XY) and three cultured samples, Wuhan (WH), Jingzhou (JZ) and Nanjing (NJ) were randomly selected for genetic analysis. Twelve ISSR primers were used for screening the six populations and 110 loci were obtained. The polymorphic loci were estimated to be 54%, 56.3%, 58.2%, 60.6%, 69.5% and 71% in NJ,WH, JZ, XT, HG and XY samples, respectively. Average heterozygosity value varied from 0.1956 to 0.2449. The three wild samples showed higher genetic diversity than the cultured samples (P < 0.05), including polymorphic bands (PPB), observed number of alleles per locus (_to), effective number of alleles per locus (Ne), Nei’s gene diversity index (H) and Shannon’s information index (I).     

Mating system and size advantage of male mating in the protogynous swamp eel Monopterus albus with paternal care

In fish with paternal care, protogynous sex change (female to male) is rare and has only been reported from species with haremic polygyny. The swamp eel, Monopterus albus, is a protogynous fish with paternal care, but little is known about its mating system. To understand protogyny in this species, we examined the mating system and male size advantage in mating in M. albus under semi-natural condition. Females swam over wide ranges and visited multiple male nests. Males defended a narrow territory around nests against other males that approached nests; at these nests, males courted and accepted visiting females. After spawning inside nests, caring males continued to perform courtship activities, and multiple breeding was observed. These observations suggest that the M. albus mating system is male-territory-visiting (MTV)-polygamy. Larger males had nests, and mated more frequently compared with small males. Because small initial males of this species are not found in nature, and because M. albus does not engage in sneaking tactics, larger nesting males do not suffer from reproductive parasitism. Thus, protogyny in this fish is likely consistent with the predictions of the size-advantage model. Biting attacks by territorial males of this predatory fish seriously wounded intruding males, occasionally resulting in the death of the intruder. We discuss the possibility that sexual differences in mortality rates in small fish may facilitate the evolution of protogyny in this species. Protogyny of the swamp eel is, to our knowledge, the first example of an MTV-polygamous mating system in a fish with paternal care.     

黄鳝气呼吸代谢的研究

测定了黄鳝气呼吸状态下 ,2 5～ 2 7℃时的能量代谢情况。结果 ,表明平均耗氧率为 6 3 6 4mg/kg·h ,平均耗氧量 2 .81mg/尾·h ,体重与耗氧量之间的直线回归方程为 y =1.32 +0 .0 3x ;个体越大 ,耗氧量越大 ,个体越小 ,耗氧率越高。同时发现 ,黄鳝的耗氧率随环境温度变化及昼夜节律交替而变化。     

Nitrogen metabolism and excretion in the swamp eel, Monopterus albus, during 6 or 40 days of estivation in mud

Monopterus albus inhabits muddy ponds, swamps, canals, and rice fields, where it can burrow into the moist earth, and it survives for long periods during the dry summer season. However, it had been reported previously that mortality increased when M. albus was exposed to air for 8 d or more. Thus, the objective of this study was to elucidate the strategies adopted by M. albus to defend against ammonia toxicity during 6 or 40 d of estivation in mud and to evaluate whether these strategies were different from those adopted by fish to survive 6 d of aerial exposure. Ammonia and glutamine accumulations occurred in the muscle and liver of fish exposed to air (normoxia) for 6 d, indicating that ammonia was detoxified to glutamine under such conditions. In contrast, ammonia accumulation occurred only in the muscle, with no increases in glutamine or glutamate contents in all tissues, of fish estivated in mud for 6 d. Similar results were obtained from fish estivated in mud for 40 d. While estivating in mud prevented excessive water loss through evaporation, M. albus was exposed to hypoxia, as indicated by significant decreases in blood P(O(2)), muscle energy charge, and ATP content in fish estivated in mud for 6 d. Glutamine synthesis is energy intensive, and that could be the reason why M. albus did not depend on glutamine synthesis to defend against ammonia toxicity when a decrease in ATP supply occurred. Instead, suppression of endogenous ammonia production was adopted as the major strategy to ameliorate ammonia toxicity when M. albus estivated in mud. Our results suggest that a decrease in O(2) level in the mud could be a more effective signal than an increase in internal ammonia level during aerial exposure to induce a suppression of ammonia production in M. albus. This might explain why M. albus is able to estivate in mud for long periods (40 d) but can survive in air for only <10 d.     

Cryptic diversification of the swamp eel Monopterus albus in East and Southeast Asia, with special reference to the Ryukyuan populations

The swamp eel Monopterus albus is widely distributed in tropical and subtropical freshwaters ranging from Southeast Asia to East Asia, and is unique in its ability to breathe air through the buccal mucosa. To examine the genetic structure of this widespread species, molecular phylogenetic analyses of mitochondrial 16S rRNA sequence (514 bp) were conducted for 84 specimens from 13 localities in Southeast and East Asia. The analyses showed clearly that this species can be genetically delineated into three clades based on geographical populations [China–Japan (Honshu + Kyushu), Ryukyu Islands, and Southeast Asia clades], with each clade exhibiting its own reproductive behavior. Therefore, “M. albus” is believed to be composed of at least three species. The Southeast Asia clade with the highest genetic diversity may include more species. The Ryukyu clade was estimated to have diverged more than 5.7 million years ago, suggesting that the Ryukyuan “M. albus” is native. In contrast, in the China–Japan clade, all haplotypes from Japan were closely related to those from China, suggesting artificial introduction(s).     

The atretic structures in the gonads of the rice-field eel (Monopterus albus) during natural sex-reversal

The gonad of the protogynous, hermaphroditic teleost, Monopterus albus were examined histologically at monthly intervals throughout one year. In particular, the epithelium of the maturing follicles of the female and the atretic follicles in the female, intersex and male were studied. Atretic follicles were common in the gonads and were classified as corpora atretica types 1 to 5 according to histological criteria. In addition, other regressive structures were observed in the gonads of some males. The histology and the frequency of occurrence of the atretic structures in the three sexual phases is described and discussed.     

Ag-staining pattern, FISH and ISH with rDNA probes in the rice field eel (Monopterus albus Zuiew) chromosomes

The present paper reports the Results of rice field eel (Monopterus albus Zuiew) chromosomal analysis by Ag-staining techniques, FISH and ISH with 18S rDNA. Both the Ag-NORs and the hybridization signals were observed on the pericentromeric region of chromosome pairs 3 and 7. The Ag-NORs and the hybridization signals on homologous chromosomes 3 and 7 were corresponding to each other. And rDNA genes were mapped to bivalents 3q12-q24 and 7q14-q26. No heteromorphic sex chromosome pair was identified. The Results obtained were discussed with respect to the feature of Ag-NORs and the position of rDNA genes on chromosome pairs 3 and 7.     

Seasonal population dynamics of Pallisentis (Neosentis) celatus (Acanthocephala: Quadrigyridae) in the intestine of the rice-field eel Monopterus albus in China

Studies on the seasonal population dynamics of Pallisentis (Neosentis) celatus (Acanthocephala: Quadrigyridae) in the intestine of the rice-field eel Monopterus albus from the paddies and ditches in the Dong-ting Lake basin of China, were carried out with samples taken from June 2002 to May 2003. Prevalences were above 21% in all seasons sampled and with a distinct seasonal trend, which was highest (45.81%) in the spring and decreased by degrees. The mean intensity of infection was above 4.0 worms per fish. The maximum intensity of worms recovered from a single fish was 86 in the autumn of 2002. No significant seasonal differences were found in mean intensities, and differences in the mean abundance between winter and spring, winter and autumn were significant. Over-dispersed distributions of P. (N.) celatus in the host population, due to heterogeneity and feeding habits, were observed in all seasons. The size composition of both sexes of P. (N.) celatus showed males between 2.0 mm and 14.0 mm and females between 2.2 mm and 22.2 mm, with the main recruitment phase in the worm populations occurring in the summer and autumn, especially in the autumn, with the lowest recruitment occurring in the winter. The maturation and copulation of worms were mainly focused in the spring season. The sex ratio of female to male was both high in summer (1.09:1) and autumn (1.08:1). The higher proportion of females and the change in the worm sex ratio in summer can be attributed to the reduced longevity of male worms. As immature male worms exhibit a higher proportion of the worm population than females in all seasons, further studies are needed to determine if such a situation compensates for the shorter life span of males.     

Isolation and characterization of polymorphic microsatellites in a sex‐reversal fish,rice field eel (Monopterus albus)

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.     

黄鳝IRF-4和IRF-10的表达研究

目的:干扰素调节因子是一类能够调控干扰素及其相关免疫基因表达的转录因子,研究黄鳝干扰素调节因子的结构及表达有助于阐明黄鳝抗病毒的机理。方法:利用PCR扩增技术获得了黄鳝干扰素调节因子10(IRF-10)和IRF-4的部分cDNA序列,再利用半定量PCR技术检测了黄鳝不同发育阶段、不同组织IRF-10和IRF-4的表达。结果:IRF-10和IRF-4在黄鳝三个不同的发育阶段表达量基本一致,但两者在黄鳝不同组织表达呈现明显的差异,IRF-10组成型表达于黄鳝各个组织中,而IRF-4仅在肠、中肾和脑中呈现很高的表达,其他组织表达很弱。结论:IRF-10组成型地表达于黄鳝各个组织,且表达量很高;而IRF-4中仅在主要免疫器官表达,且表达量较弱。     

黄鳝血液生理参数的研究

报道了健康黄鳝血液的几项生理参数。结果 ,红细胞 2 .37× 10 12 L ,白细胞 4.16× 10 9L ,血栓球 6 1.6× 10 9L ,血红蛋白 134 .5 gL ,红细胞最大脆性 0 .35 % (NaCL溶液 ) ,血沉 1.0 5mmh ,凝血时间 1.75min。并将黄鳝的血液生理参数与其它几种鱼类作了对比分析     

Age and growth of Monopterus albus Zuiew, 1793 (Synbranchidae)

Age and growth of Monopterus albus (Zuiew, 1787) in Lake Nanhu, Wuhan, Hubei Province, China, were studied from January to December 2007. A total of 418 samples were collected ranging from 18 to 86 cm total length (TL). Among these samples, ages of female were 1 ⁺ –5 ⁺ years while males were 3 ⁺ –9 ⁺ years as estimated by basihyal. The length–weight relationships and the von Bertalanffy growth curve were described for all individuals as: W_T = (2 × 10^?7) TL^3.2366 and L_t = 104.1{1‐e^{?0.108 (t + 1.625)}}. To the best knowledge of the authors, this study presents the first reference on the relationship between age and growth of this species for the management of fishery resources.     

Pituitary extract of the ricefield eel Monopterus albus (Synbranchidae, Teleostei) exhibits gonadotropic activity in the classes Mammalia, Aves, Reptilia and Amphibia

Pituitary extract of the ricefield eel Monopterus albus demonstrated gonadotropic activity in mammals and non-mammalian vertebrates. Using the rat as the recipient, FSH activity was detected in Monopterus pituitaries in the HCG augmentation test and LH activity in the ovarian ascorbic acid depletion test. Cyclic AMP level in superovulated ovaries, ovarian lactate production and glucose uptake in vitro, plasma testosterone level in males, testicular enzymes, ventral prostate weight and other androgen-dependent parameters were stimulated after treatment with Monopterus pituitary extract. Testicular and ovarian 32P5+ uptake in the chick, testicular weight in the grass turtle Chinemys reevesi, and ovulation in the amphibians Xenopus laevis and Rana tigrina were enhanced. Both the FSH-like and LH-like activities in Monopterus pituitaries were sensitive to proteolytic enzymes and chemicals that attack the disulfide linkage, carbohydrate moiety, tyrosine, tryptophan and histidine residues. This constitutes the first report of dual gonadotropic activities elicited by a teleost pituitary extract in the mammal in vivo.     

Construction of a BAC library and identification of Dmrt1 gene of the rice field eel, Monopterus albus

A bacterial artificial chromosome (BAC) library was constructed using nuclear DNA from the rice field eel (Monopterus albus). The BAC library consists of a total of 33,000 clones with an average insert size of 115 kb. Based on the rice field eel haploid genome size of 600 Mb, the BAC library is estimated to contain approximately 6.3 genome equivalents and represents 99.8% of the genome of the rice field eel. This is first BAC library constructed from this species. To estimate the possibility of isolating a specific clone, high-density colony hybridization-based library screening was performed using Dmrt1 cDNA of the rice field eel as a probe. Both library screening and PCR identification results revealed three positive BAC clones which were overlapped, and formed a contig covering the Dmrt1 gene of 195 kb. By sequence comparisons with the Dmrt1 cDNA and sequencing of first four intron-exon junctions, Dmrt1 gene of the rice field eel was predicted to contain four introns and five exons. The sizes of first and second intron are 1.5 and 2.6 kb, respectively, and the sizes of last two introns were predicted to be about 20 kb. The Dmrt1 gene structure was conserved in evolution. These results also indicate that the BAC library is a useful resource for BAC contig construction and molecular isolation of functional genes.     

Development of the neo-morphic air breathing organ in the swamp-eel, Monopterus albus (Zuiew)

The embryonic gill material derived from the 1st gill arch gives rise to the respiratory epithelium of the mouth cavity for aerial respiration in Monopterus albus. A comprehensive gill mass formed by mixing of the embryonic gill materials derived from the dorsal ends of the gill arches (II to V) gives rise to the fused gill filaments on the 1st and IInd gill arches that subserve the purpose of utilizing O2 from air or water.