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Context. The Indo-Pacific eel (Anguilla marmorata) is a widely distributed and commercially valuable species across ecological regions worldwide. Overfishing and habitat loss are leaving the Indo-Pacific eel in a risky situation and raising a high demand for conservation. Previous research has found relationships between the Indo-Pacific eel's migration patterns and environmental factors. However, there is still a need to advance the discovery of its spatial distribution by using diverse environmental and ecological datasets and modelling its growth in terms of different environmental characterizations. Aims & Methods. Here, we compared machine learning (ML) CatBoost (CB) and the multivariate linear model to investigate the relationship between spatial distribution, Indo-Pacific eel development stages, and environmental factors in central Vietnam. Key results. Our results show that CB detected the Indo-Pacific eel at high accuracy (Overall Accuracy (OA) = 0.9, F1 = 0.88, AUC = 0.97) and estimated the total length at different confidence levels (R2 ranging from 0.51 to 0.70), demonstrating superior performance to the multivariate linear model. Conclusions & implications. This study highlights the potential use of ML models in species distribution mapping and modelling growth patterns to support conservation efforts of Indo-Pacific eels in their natural habitats. [ABSTRACT FROM AUTHOR]

Two new cutthroat eel species are described from Vietnam. Dysomma intermediumsp. nov. has a relatively long trunk, being about half of head length and anal‐fin origin more than twice pectoral‐fin length behind the pectoral‐fin tip; pectoral fin well developed; dorsal‐fin origin over or slightly in front of base of pectoral fin; two intermaxillary teeth; four or five compound teeth on ethmovomer; single row of seven or eight teeth on lower jaw; total lateral‐line pores 70–76; and 21 pre‐anal and 118–124 total vertebrae. Dysommina brevissp. nov. differs from congeners by having a trunk shorter than head length, its length 11.1%–11.8% TL; a short pre‐anal length 24.6%–25.6% TL, eye diameter 11.8%–12.3% head length; three large and one or two small teeth on ethmovomer; and fewer teeth on the upper and lower jaws. In addition, a specimen representing the first record of Dysommina orientalis in Vietnamese water is documented. [ABSTRACT FROM AUTHOR]

A species of catfish belonging to the Anguilla genus called Anguilla marmorata has long been exploited and grown in Vietnam. Marbled eels are regarded as a specialty seafood species with several therapeutic and nutritive benefits. This study used High-Performance Liquid Chromatography (HPLC) to identify various biochemical and nutritional ingredients in A. marmorata collected in its natural habitat. There was 16 different amino acids analysed in the muscle, skin, and mucus of marbled eels at the rates of 14.01%, 5.48%, and 9.96%, respectively. Twenty-four fatty acids were found in muscle and skin, while only nine fatty acids were detected in the mucus with proportions of 11.93, 25.91, and 0.37 g/100 g, respectively. Six different vitamins (A, B3, B5, D3, C, E) are found in the muscle of the eel; five types of vitamins (A, B3, B5, D3, E) were detected in the skin; and three vitamins (B3, B5, C) are found in mucus. Using HPLC analysis has shown remarkable effectiveness in micronutrient analysis in nutritional research. The results will increase our knowledge of the nutritive benefits of the A. marmorata and point the way toward the creation of functional foods and cosmetics with natural ingredients that may be used on people. [ABSTRACT FROM AUTHOR]

The Marbled Eel (Anguilla marmorata) has a widespread distribution with a complex migration life cycle There were 350 individuals of sizes from 120 to 1137 mm were analysed on characteristic morphology at 4 developing stages: juvenile, fingerling, pre-adulthood and adulthood. Morphological indicators: total length (TL), head length (HL), dorsal fin origin (PD), anal fin origin (PA), distance from dorsal to anal fin (AD), distance from pectoral fins to dorsal fin (PDH), body length (TR), eye diameter (E), tail length (T) and eye distance (IO), colour characteristics and 10 characters were standardized against the LT or LH ratios determine 95.664% of morphological differences between individuals in the study population based on principal component analysis and hierarchical cluster analysis tools. Phylogenetic tree with five morphological clusters with distance > 2.0 built a high genetic diversity. The difference of clusters is related to the morphology at different stages. Cluster 1 corresponds to the morphological characteristics at the fingerling stage (TL = 260–552.0 mm); cluster 3 is the pre-adult stage (TL = 324.6–533.9); cluster 4 is the juvenile stage (TL = 120.0–255.0); and clusters 2 and 5 for pre-adult and adult at reproductive migration (TL > 400). [ABSTRACT FROM AUTHOR]

The Mekong Delta region of Vietnam has great potential for agricultural development thanks to natural incentives. Many livestock industries have developed for a long time and play an important role in the country with many agricultural export products. In the era of breakthrough technologies and advances in information technology, many techniques are used to support the development of smart agriculture. In particular, computer vision techniques are widely applied to help farmers save a lot of labour and cost. This study presents an approach for counting eels based on Mathematical Morphology Operations and Boundary Detection from images of breeding eels captured with the proposed photo box. The proposed method is evaluated using data collected directly from a breeding eel farm in Vietnam. The authors of the research evaluate and investigate the length distribution of eels to select the appropriate size for counting tasks. The experiments show positive results with an average Mean Absolute Error of 2.2 over a tray of more than 17 eels. The contribution of the research is to provide tools to support farmers in eel farms to save time and effort and improve efficiency. [ABSTRACT FROM AUTHOR]

Recently, suspected ciguatera fish poisoning (CFP) cases caused by the consumption of moray eels, popular seafood for locals and tourists, have been reported in Viet Nam. However, little is known about ciguatoxins (CTXs) in these marine fish. In May 2020, 119 specimens of six moray eel species were collected for CTX detection from Ly Son Island (site 1), Ninh Hai Coast (site 2), Phu Quy Island (site 3), and Spratly Islands (site 4), where suspected CFP from moray eel consumption have occurred. CTX-1B was detected by liquid chromatography–mass spectrometry (LC/MS) analysis in 12 specimens belonging to four Gymnothorax species: (G. fimbriatus, G. flavimarginatus, G. javanicus, and G. undulatus), accounting for about 10% of the total specimens. Remarkably, CTX-1B levels detected in all toxic specimens were beyond the safety threshold of 10 pg/g CTX-1B equivalent. The highest occurrence was observed at site 4 (15.6%) (n = 45), followed by site 1 (10.0%) (n = 40) and site 2 (6.3%) (n = 16); whereas no CTX-1B was detected in any specimens (n = 18) from site 3. These results, for the first time, report the presence of CTX-1B, indicating a CFP risk in Viet Nam from consumption of moray eels. [ABSTRACT FROM AUTHOR]

The giant mottled eel, Anguilla marmorata, is at high risk of extinction due to overfishing of glass eels and elvers to provide stock for eel farming. In Vietnam, information on the genetic diversity and population structure of this species, which is necessary for resource management, is limited. In order to address this paucity of information, sequencing of the entire mitochondrial control region (mtDNA) was carried out for 176 individuals collected from central Vietnam. The sequences were investigated using various genetic, phylogenetic and population analyses. A total of 165 distinct haplotypes were identified. The percentage of variation within and among populations was 99.26% and 0.74%, respectively. The fixation index was low (0.007) and not significant (p = 0.096). Therefore, panmixia and a lack of significant population genetic structuring seem likely for A. marmorata in central Vietnam. Most sampled eels were genetically similar to eels found in North Pacific populations (Japan, Taiwan and the Philippines), except for one sample from Quang Tri and two samples from Binh Dinh, which had high values of genetic identity (97% to 99%) with South Pacific populations (Tahiti, Fiji, New Caledonia and Papua New Guinea). Taken together, we suggest that A. marmorata from the North and South Pacific populations co-exist in central Vietnam. [ABSTRACT FROM AUTHOR]

Giant mottled eel (Anguilla marmorata) farming in Vietnam is a multistage process starting from wild harvest of glass eels through the so‐called "hatcheries" and distribution centres from which individuals are transferred to rearing farms and subsequently sold by one eel farm to another every 3–5 months. The information on viral agents spread and persistence in the Vietnamese eel aquaculture is scarce. Therefore, the mortality of A. marmorata at the Van Xuan Farm was the prerequisite to identify the possible aetiologic agent and additionally to formulate first recommendations for viral disease screening in the Vietnamese eel aquaculture. Juvenile giant mottled eels with haemorrhagic lesions in the skin and liver, and hyperaemia of the gut were tested with qPCR and end‐point PCR for AngHV‐1 presence. Here, we report the first detection of AngHV‐1 associated with mortality in giant mottled eel in winter and spring seasons. On the basis of the obtained results, we recommend to test eel seeds in "hatcheries," since tropical eel farms operate in interconnected scheme and monitoring of AngHV‐1 prevalence requires well‐implemented measures. Disease screening in the rearing centres and on‐growing facilities should be based on everyday health checks, including by‐catch fish used as a base of the feeding programmes at eel farms in Vietnam. [ABSTRACT FROM AUTHOR]

A new snake eel, Ophichthus longicorpus, is described from 13 specimens from Lương Sơn, Nha Trang, Vietnam. It is distinguished by having dorsal-fin origin situated at 4.4‒6.7 pectoral-fin length behind head; anus situated at about middle of total length; trunk very long, 4.1‒4.9 head length; head length 10.5‒12.2 in TL; posterior nostril above upper lip, covered by a large flap extending well below the edge of mouth gape; pectoral fin small, pointed posteriorly; no barbel on upper lip; cephalic sensory pores: SO 1 + 4, POM 6 + 2; teeth moderately large and conical, biserial anteriorly and uniserial posteriorly on both jaws and vomer; body colour yellowishbrown dorsally and grayish-brown ventrally; dorsal fin light grayish with indistinct white margin; anal fin white with slightly grayish base; and total vertebrae 156–164, mean vertebral formula 27-68-159. Specimens of Echelus polyspondylus McCosker & Ho are newly reported from Vietnam. [ABSTRACT FROM AUTHOR]

Strophidon McClelland is a muraenid genus with characteristic appearance of a very elongated body, a large mouth cleft and anteriorly placed eyes. The nomenclature and taxonomic history of species within Strophidon are contentious and its members are easily misidentified. In the present study, species of the genus Strophidon are revised based on morphological and molecular data, and five species are considered valid, including S. dawydoffi Prokofiev, S. dorsalis (Seale), S. sathete (Hamilton), S. ui Tanaka and a new species, S. tetraporus. Strophidon tetraporussp. nov. is described based on 15 specimens from Indonesia, the Philippines, Taiwan and Vietnam with the unique characteristic of the constant presence of the fourth infraorbital pore among species of Strophidon. The intraspecific variation of vertebral formula within S. dorsalis is discussed based on molecular data. Muraena macrurus Bleeker and Thyrsoidea longissima Kaup are synonyms of S. sathete that can be distinguished from the most similar congener S. ui by a longer tail, smaller eyes and more inner maxillary and inner dentary teeth. A key to identify species of Strophidon is provided. The distribution and maximum size of each species are also re‐evaluated. [ABSTRACT FROM AUTHOR]

Tropical anguillid eels account for two-thirds of all species in the genus Anguilla, however information on the species diversity, biogeography, and life histories is very limited. The anguillid eels found in Southeast Asian waters, i.e. Malaysia, Thailand and Vietnam were identified using molecular genetic analysis after morphological observation. This is the first record of the occurrence of A. marmorata in Thailand and Vietnam that was confirmed by both morphological and molecular genetic analyses. The molecular phylogenetic tree and the haplotype network of A. marmorata in Malaysia, Thailand and Vietnam suggested that the eel might be transported from the western North Pacific spawning area. We also propose possible dispersion and migration of A. marmorata into Southeast Asian waters. [ABSTRACT FROM AUTHOR]

Five specimens of Gymnothorax longinquus (Whitley, 1948) were collected from a fish market and a fish landing site in Tac Cau and Ha Tien, southern Vietnam. These specimens represent the first record of G. longinquus in Vietnam, and further support a previously uncertain record in Thailand. The specimens collected are described and illustrated. Gymnothorax longinquus may prefer muddy shallow water from northern Australia to the Gulf of Thailand. [ABSTRACT FROM AUTHOR]

Fish movements between aquatic habitats of different salinity ranges (fresh, estuarine, marine) by the tropical catadromous eels Anguilla bicolor bicolor and A. bicolor pacifica were examined by analysing the otolith strontium and calcium concentrations of yellow (immature) and silver (mature) stage eels collected in south‐east Asian (Indonesia, Malaysia and Vietnam) waters. The ratios suggest that all migratory‐type eels, including freshwater, brackish water and marine residents, pass the river mouth. However, the habitat preference was different among the sites (countries). In Indonesia and Vietnam, most A. bicolor bicolor and A. bicolor pacifica were either marine or brackish water residents in this study. Alternatively, most A. bicolor bicolor were freshwater residents in Malaysia; such a typical catadromous migration pattern in these eels has not been found in previous studies. The wide range of otolith Sr:Ca in both subspecies indicates that the habitat use of these tropical eels was opportunistic among fresh, brackish and marine waters during their growth phases following recruitment to coastal areas. The geographical variability of migratory histories suggests that habitat use might be determined by the inter and intraspecific competition and environmental conditions at each site. [ABSTRACT FROM AUTHOR]

This study investigated trace metals in water, sediment, and various organs of the mature eel Anguilla marmorata in the Ba River, Vietnam. The metal concentrations in water and sediment did not exceed the Vietnam water criteria and sediment background concentration, except for Mn and Pb in sediment. The results of metal analysis in eel specimens indicated that the liver and kidney were the dominant organs for almost all trace metals, whereas muscle tended to accumulate high levels of Hg and approximately 87.4–100% of Hg was methylmercury. A strong positive correlation between mercury levels in muscle and age were found, but there was no correlation between mercury and body size. Interestingly, a high concentration of Zn was found in the gonad and liver; this indicated that high levels of Zn in the liver might play a physiologically important role in the eel’s biological mechanisms during gonadal maturation. Though almost none of the metal concentrations in the muscle exceeded the reference doses of the U.S. EPA, approximately 80% of eels from the river contained mercury exceeding the recommended levels (0.30 μg/g) of the U.S. EPA and might present a risk for human consumption. [ABSTRACT FROM AUTHOR]

In order to understand the present status of heavy metal contamination and the risk associated with human consumption, commercial freshwater eels in Vietnam were examined. The concentration of eight elements (Cr, Mn, Co, Cu, Zn, Sr, Cd, and Pb) was determined in muscle tissue of tropical eel Anguilla marmorata collected in four provinces, Quang Tri, Quang Ngai, Binh Dinh, and Phu Yen, from the central part of Vietnam. Concentrations of Cu, Zn, Cd, and Sr were found to be highest, whereas Co concentration showed the lowest at Quang Tri. Cr was recorded to be lowest in Quang Ngai, while the amounts of Mn and Pb did not vary among locations. Although the metal concentrations in the muscle of A. marmorata did not represent a risk for human consumption, elevated Cd concentrations in Quang Tri related to agriculture activities suggest that further investigations should be undertaken to clarify the potential risk to the eel population. [ABSTRACT FROM AUTHOR]

Human infections with Gnathostoma spinigerum frequently occur in southern Vietnam. Previous investigations have implicated infected swamp eels (Monopterus albus) as an important source of infection to humans. Because aquaculture of M. alba is an important farming activity in Vietnam, a 2-yr study was carried out to assess the relative importance of farmed and wild eels as potential sources of gnathostome infections in humans. Eels sold for public consumption in markets in southern provinces were examined between November 2005 and August 2007. Although no infections were detected in 1,020 cultured eels and 1,021 wild-caught eels collected from November 2005 to September 2006, larval G. spinigerum (AL3) infections were first detected in September 2006 in 28 of 230 wild-caught eels (12.2%) obtained from markets in Long An province and the Hoc Mon district of Ho Chi Minh City. Subsequently, monthly surveillance of wild-caught eels from these markets was carried out through August 2007. Prevalence of AL3 varied monthly, ranging from 0.8 to 19.6%. Both prevalence and infection intensity were higher during the latter part of the rainy season (August-October). These results demonstrate that potentially zoonotic G. spinigerum larvae are common in wild eels in southern Vietnam and present a risk to consumers of raw fish dishes, especially during the annual rainy season. This information could help target public health education efforts in the region. The basis for the seasonal variation on eel infections is not known, but may be related to climate effects (flooding, higher temperatures) on intermediate host species ecology. [ABSTRACT FROM AUTHOR]

A new species of the synaphobranchid genus Atractodenchelys is described based on 31 specimens collected off Quy Nhon and Nha Trang, southern Vietnam. The new species can be distinguished from the only two congeners in the genus by having much fewer total vertebrae (155‒158, vs. 168‒172 in A. phrix and 186‒199 in A. robinsorum), a relatively long head (head length 10.1‒12.3% TL), a relatively short snout (30.0‒35.8% HL), head longer than trunk length (vs. about equal in length in both species); and 5‒6 compound teeth on vomer (vs. 7‒8 in A. robinsorum).

Two new species of elongate unpatterned moray eels related to Gymnothorax prolatus are described. Gymnothorax pseudoprolatus sp. nov. is described from one specimen collected off southwestern Taiwan and Gymnothorax vietnamensis sp. nov. is described from seven specimens collected off central Vietnam. Both differ from other species in the group in the number of vertebrae, position of anus, and dentition. Gymnothorax pseudomelanosomatus Loh et al., 2015 is reported from southern Taiwan for the first time; it was previously known from the type series collected off the northeastern tip of Taiwan. Gymnothorax angusticauda (Weber de Beaufort 1916) is reported for the first time in Taiwan and the Philippines.