Analysis of the effectiveness of control measures against Schistosoma mekongi using an intra- and inter-village model in Champasak Province, Lao PDR

Schistosomiasis mekongi is prevalent in the Khong district of Lao PDR, made up of one big island, Khong, and numerous small islands in the Mekong River. Schistosoma mekongi is spread by Neotricula aperta as the intermediate host along the Mekong River. Therefore, even if an epidemic of S. mekongi were stamped out in a certain village, infection may recur if the source of infection is a village located in the upper reaches of the Mekong River. The purpose of this study was to construct a mathematical model for the transmission of S. mekongi among villages from the upper to lower Mekong River to estimate the effect of control measures against it. The chief characteristic of the present model is competence in dealing with the spread of infection among villages through the Mekong River in consideration of the reduction in longevity of cercariae and miracidia and their diffusion in the river. The model also takes into account seasonal fluctuation in the water level of the Mekong River, which affects human behavior in terms of water contact. The results of simulations indicated that the prevalence of schistosomiasis mekongi would be suppressed to a low level for a long time in a village further downstream when universal mass treatment is performed in villages further upstream simultaneously.     

Long distance migration and marine habitation in the tropical Asian catfish, Pangasius krempfi

A synthesis of catch data from southern Laos and life-history information indicate that adult Pangasius krempfi , an important Asian catfish, migrates up the Mekong River from the South China Sea in Vietnam past Cambodia, arriving in southern Laos each year in May. Strontium concentrations in the otoliths of river-caught P. krempfi are, on average, three to four times higher than the levels of strontium in the otoliths of related freshwater species, indicating marine and estuary habitation for fish caught in southern Laos. Pangasius krempfi muscle tissue samples from the same fish also exhibit stable isotope (δ¹⁵N and δ¹³C) values characteristic of marine environments. The results of this investigation support the conclusion that P. krempfi is anadromous, spending a part of its life at sea and in the brackish water of the Mekong Delta before returning to spawn in fresh water. The fish travels at least 720 km to the Khone Falls in southern Laos, and possibly further. Spawning probably occurs in fresh water from June to August at which time young fish move down the Mekong River to the Mekong Delta. The data answer a previously unresolved question (the long-distance migratory behaviour of P. krempfi ) and have important implications for the management and conservation of Mekong River fishes.     

Population subdivision in Siamese mud carp Henicorhynchus siamensis in the Mekong River basin: implications for management

A molecular approach was employed to investigate stock structure in Siamese mud carp Henicorhynchus siamensis populations collected from 14 sites across mainland south-east Asia, with the major focus being the lower Mekong River basin. Spatial analysis of a mitochondrial DNA fragment (ATP ase 6 and 8) identified four stocks in the Mekong River basin that were all significantly differentiated from a population in the nearby Khlong River, Thailand. In the Mekong River basin, populations in northern Lao People's Democratic Republic and northern Thailand represent two independent stocks, and samples from Thai tributaries group with those from adjacent Mekong sites above the Khone Falls to form a third stock. All sites below the Khone Falls constituted a single vast stock that includes Cambodia and the Mekong Delta in Vietnam. While H. siamensis is considered currently to undertake extensive annual migrations across the Mekong River basin, the data presented here suggest that natural gene flow may occur over much more restricted geographical scales within the basin, and hence populations may need to be managed at finer spatial scales than at the whole-of-drainage-basin level.     

Strong population genetic structure and its management implications in the mud carp Cirrhinus molitorella, an indigenous freshwater species subject to an aquaculture and culture-based fishery

This study investigated population genetic structure and diversity of mud carp Cirrhinus molitorella, a species widely used in aquaculture and culture-based fisheries in China and Mekong River riparian countries. Seven newly developed and one published microsatellite DNA markers were used to analyse samples from six wild locations, four hatchery broodstocks and one farmed site from the Mekong, Red and Pearl Rivers. Significant genetic structure was detected in C. molitorella, with isolation-by-distance being a strong force in the Mekong. Pair-wise F(ST) , Fisher's exact tests for population differentiation, permutation tests and individual-based structure analysis all support the recognition of a sample originating from Toul Krasaing Lake (Cambodia) and one between Kratie and Stung Treng (Cambodia) as distinct from the remainder of the sampled range. Samples from the main upper Mekong and the Nam Khan River were significantly differentiated, but on a time scale inferred to be short (i.e. by genetic drift, not sufficient for evolution of new microsatellite alleles). The Mekong stock of C. molitorella was strongly differentiated from those from the Red and Pearl Rivers, inferred to be on an evolutionary time scale. Finer-scale sampling is warranted to further improve the understanding of genetic interactions among fish from the Mekong and its tributaries. Detailed studies on the ecology of C. molitorella (e.g. migration pathways and preferred spawning habitats) would provide useful information to explain the patterns of genetic structure detected here, and deepen insights about evolutionary distinctiveness of the population units.     

Fish and fisheries in the Upper Mekong: current assessment of the fish community, threats and conservation

The Mekong flows north to south, through six countries in south–east Asia. Many studies have concentrated on fish and fisheries in the Lower Mekong, which has been identified as one of the largest inland fisheries in the world with an incredibly rich diversity of species. In contrast, fish and fisheries in the Upper Mekong (Lancang River) have remained relatively undocumented. In this paper, we synthesized information on freshwater fish biodiversity and fisheries in the Upper Mekong and documented 173 species and subspecies (including 87 endemic species) among 7 orders, 23 families and 100 genera. We divided the Upper Mekong into 17 sub-basins based on Digital Elevation Model (DEM) and then used fish species data to cluster the sub-basins. Four parts (the headwater, the upper reach, the middle reach and the lower reach) and one lake have distinct fish species communities associated with them. There was a linear relationship between fish species (x) and endemic species (y) as y = 0.5464x − 3.2926. Relationship between species number or endemic species number (y) and mean altitude (x) can be described as y = −54.352 ln(x) + 460.79 or y = −30.381 ln(x) + 253.85, respectively. Fisheries kept as about 6,000 t from 1989 to 1998, and then steadily increased to 10,000 t in 2004. We reviewed the overall threats to the Upper Mekong fish and fisheries, and found that hydrological alteration is the largest threat in the basin, followed by over fishing and the introduction of exotic species. In terms of specific river sections, water pollution was the most serious threat to fishes in the upper reach of the Upper Mekong, whilst migratory fishes in the lower reach of the Upper Mekong are seriously threatened by the construction of cascade dams. The Buyuan River and the Nanla River were identified as important feeding and spawning habitats for upstream migrant species and should be considered as a priority for conservation.     

中国条鳅新纪录种——Schistura porthos Kottelat,2000(英文)

在对澜沧江的亚流域罗梭江支流南星河的考察中,采集到一个中国条鳅新记录种。该物种经鉴定为Schistura porthos Kottelat,2000。该物种在罗梭江亚流域的发现延伸了其分布范围。     

Genetic differentiation and distribution routes of the bronze featherback Notopterus notopterus (Osteoglossiformes: Notopteridae) in Indochina

Mitochondrial DNA analysis was used to investigate genetic variation in the bronze featherback fish Notopterus notopterus in Indochina. Five hundred and five fish samples collected from 11 localities were separated into three genetically differentiated intraspecific groups. Chao Phraya River samples formed a distinct group. Mekong River samples were clearly separated into two different groups, namely, middle and lower Mekong groups. The lower Mekong group was closely related to Malay Peninsula group, even though the two groups are separated by a tract of ocean. F‐values (0.82–0.95) also confirmed genetic differentiation of the middle and lower Mekong groups. Although the two Mekong groups inhabit the same river basin, molecular clock calculations indicate they separated approximately 1.2 Mya, suggesting (1) evolutionary divergence before invasion of the Mekong River; (2) differences in migration routes to the river; and/or (3) differences in the timings of invasion. The complexities of historical events cannot be ignored in determinations of factors responsible for the exceptional biodiversity in the Mekong basin. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 575–582.     

Genetic variation,demographic history and phylogeography of tire track eel,Mastacembelus favus (Synbranchiformes: Mastacembelidae) in Southeast Asia

The complex climatic and geological history of Southeast Asia has been hypothesised to determine the most important aspects of the current phylogeographical structure and distribution of living organisms throughout the region. To test existing hypotheses, the genetic structure of the tire track eel, Mastacembelus favus, was investigated using 823 bp of mitochondrial DNA cytochrome b from 469 individuals from 51 localities encompassing its native range. The results classified all haplotypes into two major lineages, Lineage 1, which was further divided into Lineages 1a (lower Mekong, eastern Gulf of Thailand and Malay—Thai Peninsula), 1b (Banpakong River), 1c (Chao Phraya, Gulf of Thailand and Malay—Thai Peninsula) and 1d (Khlang Yai River), and Lineage 2, the upper reaches of the lower Mekong and the middle Mekong. Strong genetic discontinuities dated approximately 5 MYA were discovered in the Mekong with limited geographical overlap, suggesting a historically dissected drainage between two sections and species colonisation via different routes. The widespread Lineage 1 showed a strong signature of population expansion during the Pleistocene climate oscillation. Haplotype characteristics in the Malay—Thai Peninsula are hypothesised to result from postglacial dispersal from the Mekong and Chao Phraya through an extended Pleistocene drainage network.

     

Length–weight relationships of six fish species from the Lancang River,China

Length–weight relationships of six fish species are presented. Fish samples were collected from the Lancang River, in the Chinese section of the Upper Mekong River, in southwestern China. This study reports the first length–weight relationship for one of these species.     

Revision ofAcanthopsoides Fowler, 1934 (Cypriniformes: Cobitidae), with the description of new species

The genusAcanthopsoides Fowler, 1934 is revised;Neacanthopsis Smith, 1945 is placed in the synonymy ofAcanthopsoides. In addition toAcanthopsoides gracilis Fowler, 1934 andAcanthopsoides gracilentus (Smith, 1945), four new species are described in the genus. These areA. delphax of the Salween, Chao Phraya and Mekong river basins,A. hapalias of the Mekong River basin,A. molobrion from peninsular Thailand, Malaysia and Borneo, andA. robertsi from the Kapuas River basin and adjacent areas, Borneo. The known distribution of the genus includes most of Southeast Asia.Acanthopsoides gracilis, A. gracilentus, and Adelphax are sympatric: Amolobrion and A. robertsi in the Kapuas River basin andA. gracilentus, A. delphax andA. hapalias in the Mekong River basin may be also. The increase in the diversityof Acanthopsoides recognized herein may be indicative of the level of the unknown diversity of the Southeast Asian freshwater fish fauna in general.     

Maesaipsyche mekongensis sp. n. – the Third Species of the Genus from South-East Asia (Trichoptera,Arctopsychidae)

Maesaipsyche mekongensis sp. n. is described from Laos. The type series was collected near the Mekong River, which is suggestive of a potamobiontic habitat of the larvae. The male genitalic apparatus is illustrated.     

湄公河流域土壤侵蚀空间特征及其优先治理区确定

湄公河流域拥有丰富的自然生态系统,为沿岸居民提供了食物、交通等众多方面支持,在东南亚地区具有极其重要的地位。土壤侵蚀是该流域主要环境问题,易引发土地退化和河流泥沙淤积。基于气候、土壤、遥感等区域数据产品,使用通用土壤流失方程(USLE,Universal Soil Loss Equation),对湄公河流域土壤侵蚀状况及空间分布特征进行探究,并通过联合信息熵方法,确定该流域土壤侵蚀的主导因素。结果表明,湄公河流域平均土壤侵蚀模数为1.98×10~3 t km~(-2) a~(-1),属轻度侵蚀;流域内近40%区域存在不同强度的土壤侵蚀,侵蚀较严重的地区主要包括11个子流域(M4—M7、M9、T4—T6、T8、T10、T20),是未来土壤侵蚀重点治理区域。土地利用类型、坡度和海拔是该流域土壤侵蚀的主导因素,其中灌丛和裸地/稀疏植被分别为强烈和极强烈侵蚀,土壤侵蚀模数与坡度的关系为随坡度的增加呈先增加后减小的趋势,和土壤侵蚀模数与海拔的关系相同。流域内剧烈程度侵蚀发生区主要特点为:土地利用类型为裸地/稀疏植被和灌木,海拔在500—2000 m,坡度在8—25°。基于优先级理论,对湄公河子流域的优先治理次序进行排序和划分等级,共分为4个等级,达到第一级的共3个子流域。通过以上研究分析以期能为湄公河流域今后的水土保持规划和管理工作提供一定的科学参考依据。     

A new species of the genus Mekongina Fowler, 1937 (Cypriniformes: Cyprinidae) from South China

A new species of cyprinid fish, Mekongina lancangensis, is described from the upper Mekong River drainage in Southern Yunnan, China. The new species is distinguished from the other species of Mekongina occurring in the lower Mekong River drainage by possessing the following combination of characters: one pair of rostral barbels; two rows of tubercles irregularly scattered on the snout and cheeks, with two enlarged tubercles present at each side of anterior of the snout; 19–27 rostral marginal lappets; lateral line with 38–41 scales; 5·5 or 6·5 scales in transverse series from dorsal‐fin origin to lateral line; 18–20 circumpeduncular scales; snout length 31·9–36·9% head length; tip of depressed anal‐fin rays extending to the caudal‐fin base.     

MtDNA diversity of the critically endangered Mekong giant catfish (Pangasianodon gigas Chevey, 1913) and closely related species: implications for conservation

Catfishes of the family Pangasiidae are an important group that contributes significantly to the fisheries of the Mekong River basin. In recent times the populations of several catfish species have declined, thought to be due to overfishing and habitat changes brought about by anthropogenic influences. The Mekong giant catfish Pangasianodon gigas Chevey, 1913 is listed as Critically Endangered on the IUCN Red List. In the present study, we assessed the level of genetic diversity of nine catfish species using sequences of the large subunit of mitochondrial DNA (16S rRNA). Approximately 570 base pairs (bp) were sequenced from 672 individuals of nine species. In all species studied, haplotype diversity and nucleotide diversity ranged from 0.118±0.101 to 0.667±0.141 and from 0.0002±0.0003 to 0.0016±0.0013, respectively. Four haplotypes were detected among 16 samples from natural populations of the critically endangered Mekong giant catfish. The results, in spite of the limited sample size for some species investigated, indicated that the level of genetic variation observed in wild populations of the Mekong giant catfish (haplotype diversity=0.350±0.148, nucleotide diversity=0.0009±0.0008) is commensurate with that of some other related species. This finding indicates that (1) wild populations of the Mekong giant catfish might be more robust than currently thought or (2) present wild populations of this species carry a genetic signature of the historically larger population(s). Findings from this study also have important implications for conservation of the Mekong giant catfish, especially in designing and implementing artificial breeding programme for restocking purposes.     

Dasyatis laosensis,a new whiptailed stingray (family Dasyatidae), from the Mekong River of Laos and Thailand

Synopsis Dasyatis laosensis, a new species, is described from the Mekong River where it forms the border between Laos and Thailand. It is the first member of the genus Dasyatis to be described as an endemic freshwater species from Southeast Asia. Bright orange color on the ventral surface of the disc and similar meristic characters indicate that it may be closely related to Dasyatis akajei, a marine species from southern Japan and China, and to Dasyatis sp. undetermined, from the West River in Guangxi, southern China.     

Aaptosyax grypus,a new genus and species of large piscivorous cyprinids from the middle Mekong River

A new genus and species of cyprinid fishes,Aaptosyax grypus, is described from the middle Mekong River of Laos and Thailand, This large and rarely seen species reaches a full meter in length and lives in the main stem of the river. The species is a piscivore and the southernmost representative of the aspiin lineage. Among the aspiins it is unique in having a well-developed adipose eyelid and large symphyseal knob on the mandible which fits into a deep notch in the upper jaw.     

Potential Effects of Hydroelectric Dam Development in the Mekong River Basin on the Migration of Siamese Mud Carp (Henicorhynchus siamensis and H. lobatus) Elucidated by Otolith Microchemistry

The migration of Siamese mud carp (Henicorhynchus siamensis and H. lobatus), two of the most economically important fish species in the Mekong River, was studied using an otolith microchemistry technique. Fish and river water samples were collected in seven regions throughout the whole basin in Thailand, Laos and Cambodia over a 4 year study period. There was coherence between the elements in the ambient water and on the surface of the otoliths, with strontium (Sr) and barium (Ba) showing the strongest correlation. The partition coefficients were 0.409–0.496 for Sr and 0.055 for Ba. Otolith Sr-Ba profiles indicated extensive synchronized migrations with similar natal origins among individuals within the same region. H. siamensis movement has been severely suppressed in a tributary system where a series of irrigation dams has blocked their migration. H. lobatus collected both below and above the Khone Falls in the mainstream Mekong exhibited statistically different otolith surface elemental signatures but similar core elemental signatures. This result suggests a population originating from a single natal origin but bypassing the waterfalls through a passable side channel where a major hydroelectric dam is planned. The potential effects of damming in the Mekong River are discussed.     

Modelling Hydrologic Processes in the Mekong River Basin Using a Distributed Model Driven by Satellite Precipitation and Rain Gauge Observations

The Mekong River is the most important river in Southeast Asia. It has increasingly suffered from water-related problems due to economic development, population growth and climate change in the surrounding areas. In this study, we built a distributed Geomorphology-Based Hydrological Model (GBHM) of the Mekong River using remote sensing data and other publicly available data. Two numerical experiments were conducted using different rainfall data sets as model inputs. The data sets included rain gauge data from the Mekong River Commission (MRC) and remote sensing rainfall data from the Tropic Rainfall Measurement Mission (TRMM 3B42V7). Model calibration and validation were conducted for the two rainfall data sets. Compared to the observed discharge, both the gauge simulation and TRMM simulation performed well during the calibration period (1998–2001). However, the performance of the gauge simulation was worse than that of the TRMM simulation during the validation period (2002–2012). The TRMM simulation is more stable and reliable at different scales. Moreover, the calibration period was changed to 2, 4, and 8 years to test the impact of the calibration period length on the two simulations. The results suggest that longer calibration periods improved the GBHM performance during validation periods. In addition, the TRMM simulation is more stable and less sensitive to the calibration period length than is the gauge simulation. Further analysis reveals that the uneven distribution of rain gauges makes the input rainfall data less representative and more heterogeneous, worsening the simulation performance. Our results indicate that remotely sensed rainfall data may be more suitable for driving distributed hydrologic models, especially in basins with poor data quality or limited gauge availability.     

Genetic diversity of cultured populations of giant freshwater prawn (Macrobrachium rosenbergii) in China using mtDNA COI and 16S rDNA markers

Partial sequences of mitochondrial DNA 16S rDNA and COI genes (395 bp and 498 bp respectively) were sequenced from samples of ten cultured populations of Macrobrachium rosenbergii (Giant Freshwater Prawn – GFP) in Zhejiang, Guangdong and Guangxi Provinces in China and two wild populations of GFP from Mekong River and Dongnai River in Viet Nam. Five haplotypes of 16S rDNA were identified in the 360 samples. The wild populations displayed nucleotide diversity (π) of 0.0008 and 0.0003, and genetic diversity (h) of 0.3030 and 0.1310 in the Mekong River and Dongnai River respectively. The cultured populations displayed no significant genetic diversity. COI sequences identified 17 haplotypes based on 21 polymorphic sites. At this marker, the 12 populations showed a range of h from 0.1290 to 0.6940 and π from 0.0003 to 0.0073. The largest genetic distance (Da) among the 12 populations was 0.0065 (between ZJB and BT/DN populations) and the lowest Da was 0.0003 (between GDD and GDA populations). The wild populations had higher genetic diversity than the cultured populations, but three of cultured populations from Zhejiang (ZJA, ZJB and ZJC) had π higher than wild populations, because they originated from Thailand, Bangladesh and the Mekong River in Viet Nam.     

Randomized soil survey of the distribution of Burkholderia pseudomallei in rice fields in Laos

Melioidosis is a major cause of morbidity and mortality in Southeast Asia, where the causative organism (Burkholderia pseudomallei) is present in the soil. In the Lao People's Democratic Republic (Laos), B. pseudomallei is a significant cause of sepsis around the capital, Vientiane, and has been isolated in soil near the city, adjacent to the Mekong River. We explored whether B. pseudomallei occurs in Lao soil distant from the Mekong River, drawing three axes across northwest, northeast, and southern Laos to create nine sampling areas in six provinces. Within each sampling area, a random rice field site containing a grid of 100 sampling points each 5 m apart was selected. Soil was obtained from a depth of 30 cm and cultured for B. pseudomallei. Four of nine sites (44%) were positive for B. pseudomallei, including all three sites in Saravane Province, southern Laos. The highest isolation frequency was in east Saravane, where 94% of soil samples were B. pseudomallei positive with a geometric mean concentration of 464 CFU/g soil (95% confidence interval, 372 to 579 CFU/g soil; range, 25 to 10,850 CFU/g soil). At one site in northwest Laos (Luangnamtha), only one sample (1%) was positive for B. pseudomallei, at a concentration of 80 CFU/g soil. Therefore, B. pseudomallei occurs in Lao soils beyond the immediate vicinity of the Mekong River, alerting physicians to the likelihood of melioidosis in these areas. Further studies are needed to investigate potential climatic, soil, and biological determinants of this heterogeneity.