Swamp Eel Monopterus Albus Research Articles

Diversification of Toll-like receptor 1 in swamp eel (Monopterus albus)

Toll-like receptor 1 (TLR1) is a pattern recognition receptor that plays critical roles in triggering immune activation via detecting bacterial lipoproteins and lipopeptides. In this study, the genetic characteristic of TLR1 was studied for an important aquaculture fish, swamp eel Monopterus albus. The eel has been seriously threatened by infectious diseases. However, a low level of genetic heterogeneity in the fish that has resulted from a demographic bottleneck presents further challenges in breeding for disease resistance. A comparison with the homologue of closely related species M. javanensis revealed that amino acid replacement (nonsynonymous) but not silent (synonymous) differences have accumulated nonrandomly over the coding sequences of the receptors at the early stage of their phylogenetic split. The combined results from comparative analyses of nonsynonymous-to-synonymous polymorphisms showed that the receptor has undergone significant diversification in M. albus driven by adaptive selection likely after the genetic bottleneck. Some of the changes reported here have taken place in the structures mediating heterodimerization with co-receptor TLR2, ligand recognition, and/or formation of active signaling complex with adaptor, which highlighted key structural elements and strategies of TLR1 in arms race against exogenous challenges. The findings of this study will add to the knowledge base of genetic engineering and breeding for disease resistance in the eel.

Sodium acetate alleviates the liver injury induced by high carbohydrate diets in swamp eel Monopterus albus through inhibiting inflammation formation

Optimal carbohydrate level in diets could improve growth and feed efficiency，whereas HC (high carbohydrate) diets usually induce the liver injury in reared fish. While SA (sodium acetate) has demonstrated its potential to alleviate liver injury in mammals, the mechanism underlying its impact on liver health in fish remains elusive. This study aims to elucidate the effect of dietary SA on liver injury in the female Monopterus albus. In our study, groups of M. albus were fed with different diets: NC (normal, 20% carbohydrate), HC (high carbohydrate, 32% carbohydrate) and HC+A (HC supplemented with 0.2% SA) diets, in separate, for a consecutive period of 56 days. Our findings showed that HC+A diets improved growth (weight gain rate, from 263.27 ± 9.87–292.34 ± 6.18%) and FE (feed efficiency, from 67.28 ± 2.18–75.91 ± 1.90%) (P < 0.05). Simultaneously, HC+A diets alleviated the liver injury caused by HC diets, including the decrease of serum AST (aspartate aminotransferase) (P < 0.05). Meanwhile, HC-A diets decreased the relative areas of hepatic glycogen compared with the HC diets by histological analysis (P < 0.05). In addition, the transcriptomic analysis of DEG (differentially expressed genes) in liver showed that all the DEG involved in anti-inflammatory (PPARα, APOA-I) were up-regulated in HC+A group compared with NC and HC group (P < 0.05). In general, sodium acetate could improve the liver injury induced by HC diets of swamp eel through inhibiting the formation of inflammatory. Our results indicated that sodium acetate can be used as a functional additive in the application of aquatic HC diets.

Dietary Macroalgae Saccharina japonica Ameliorates Liver Injury Induced by a High-Carbohydrate Diet in Swamp Eel (Monopterus albus)

A high-carbohydrate diet lowers the rearing cost and decreases the ammonia emission into the environment, whereas it can induce liver injury, which can reduce harvest yields and generate economic losses in reared fish species. Macroalgae Saccharina japonica (SJ) has been reported to improve anti-diabetic, but the protective mechanism of dietary SJ against liver injury in fish fed a high-carbohydrate diet has not been studied. Therefore, a 56-day nutritional trial was designed for swamp eel Monopterus albus, which was fed with the normal diet [20% carbohydrate, normal carbohydrate (NC)], a high carbohydrate diet (32% carbohydrate, HC), and a HC diet supplemented with 2.5% SJ (HC-S). The HC diet promoted growth and lowered feed coefficient (FC), whereas it increased hepatosomatic index (HSI) when compared with the NC diet in this study. However, SJ supplementation increased iodine contents in muscle, reduced HSI, and improved liver injury, such as the decrease of glucose (GLU), total bile acid (TBA), and alanine aminotransferase (ALT) in serum, and glycogen and TBA in the liver. Consistently, histological analysis showed that SJ reduced the area of lipid droplet, glycogen, and collagen fiber in the liver (p < 0.05). Thoroughly, the underlying protective mechanisms of SJ supplementation against HC-induced liver injury were studied by liver transcriptome sequencing coupled with pathway analysis. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of the differentially expressed genes (DEGs), such as the acetyl-coenzyme A synthetase (acss1), alcohol dehydrogenase (adh), interferon-induced protein with tetratricopeptide repeats 1 (ifit1), aldo-keto reductase family 1 member D1 (akr1d1), cholesterol 7-alpha-monooxygenase (cyp7a1), and UDP-glucuronosyltransferase (ugt), indicated that the pathway of glycolysis/gluconeogenesis was the main metabolic pathway altered in the HC group compared with the NC group. Meanwhile, hepatitis C, primary BA biosynthesis, and drug metabolism-cytochrome P450 were the three main metabolic pathways altered by SJ supplementation when compared with the HC group. Moreover, the BA-targeted metabolomic analysis of the serum BA found that SJ supplementation decreased the contents of taurohyocholic acid (THCA), taurochenodeoxycholic acid (TCDCA), taurolithocholic acid (TLCA), nordeoxycholic acid (NorDCA), and increased the contents of ursocholic acid (UCA), allocholic acid (ACA), and chenodeoxycholic acid (CDCA). In particular, the higher contents of UCA, ACA, and CDCA regulated by SJ were associated with lower liver injury. Overall, these results indicate that the 2.5% supplementation of SJ can be recommended as a functional feed additive for the alleviation of liver injury in swamp eel-fed high-carbohydrate diets.

Asian Swamp eel Monopterus albus Population Structure and Genetic Diversity in China.

The Asian swamp eel (Monopterus albus) is one of the most widely distributed freshwater fish in China. In this study, we identified the single nucleotide polymorphisms (SNPs) of M. albus from 19 wild populations in China using restriction-site associated DNA sequencing (RAD-seq), and used SNP markers to investigate the swamp eel the genetic diversity and population genetic structure. A total of 8941794 SNPs were identified. Phylogenetic and principal component analysis suggested that the 19 populations were clustered into four groups: The Jiaoling County (JL) and Poyang Lake (PYH)populations in Group Ⅰ; the Chengdu City (CD), Dali City (YN), Eli Village (EL), Dongting Lake (DTH), Huoqiu County (HQ), and Chaohu Lake (CH) populations in Group Ⅱ; the Puyang City (PY), Chongming Island (CM), Tai Lake (TH), Gaoyou Lake (GYH), Weishan Lake (WSH), Haimen City (HM), Hongze Lake (HZH), Baiyangdian Lake (BYD), Dagushan (DGS), and Pinghu City (PH) populations in group Ⅲ; and the Lingshui County (LS) populations in Group Ⅳ. All 19 populations may have evolved from four ancestors. The genetic diversity was relatively high in CM, GYH, and HM; and low in LS, EL, and JL. The LS, and CM populations had the highest and lowest differentiation from the other populations, respectively. These findings provide new insights for germplasm resources protection and artificial breeding of M. albus.

The Complete Mitochondrial Genome of One Breeding Strain of Asian Swamp Eel (Monopterus albus, Zuiew 1793) Using PacBio and Illumina Sequencing Technologies and Phylogenetic Analysis in Synbranchiformes.

Asian swamp eel (Monopterus albus, Zuiew 1793) is a commercially important fish due to its nutritional value in Eastern and Southeastern Asia. One local strain of M. albus distributed in the Jianghan Plain of China has been subjected to a selection breeding program because of its preferred body color and superiority of growth and fecundity. Some members of the genus Monopterus have been reclassified into other genera recently. These classifications require further phylogenetic analyses. In this study, the complete mitochondrial genomes of the breeds of M. albus were decoded using both PacBio and Illumina sequencing technologies, then phylogenetic analyses were carried out, including sampling of M. albus at five different sites and 14 species of Synbranchiformes with complete mitochondrial genomes. The total length of the mitogenome is 16,621 bp, which is one nucleotide shorter than that of four mitogenomes of M. albus sampled from four provinces in China, as well as one with an unknown sampling site. The gene content, gene order, and overall base compositions are almost identical to the five reported ones. The results of maximum likelihood (ML) and Bayesian inference analyses of the complete mitochondrial genome and 13 protein-coding genes (PCGs) were consistent. The phylogenetic trees indicated that the selecting breed formed the deepest branch in the clade of all Asian swamp eels, confirmed the phylogenetic relationships of four genera of the family Synbranchidae, also providing systematic phylogenetic relationships for the order Synbranchiformes. The divergence time analyses showed that all Asian swamp eels diverged about 0.49 million years ago (MYA) and their common ancestor split from other species about 45.96 MYA in the middle of the Miocene epoch. Altogether, the complete mitogenome of this breed of M. albus would serve as an important dataset for germplasm identification and breeding programs for this species, in addition to providing great help in identifying the phylogenetic relationships of the order Synbranchiformes.

A new freshwater leech species from Asian Swamp Eel stocks in China.

Discoveries of new Hemiclepsis species (Hirudinea: Glossiphoniidae) in East and Southeast Asia were expected. A peculiar freshwater leech was found on the body surface of Asian Swamp Eel Monopterus albus (Synbranchiformes: Synbranchidae) in Jingzhou, Hubei Province, China. Here, we describe this leech species as Hemiclepsis yangtzenensis sp. nov. It could be distinguished from other congeners based on a combination of morphological features such as very small size, translucent body with dense green reticulate markings throughout dorsum, very large posterior sucker with a characteristic reticulate pattern, and two pairs of well-developed drop-like eyespots. It also represents a phylogenetic lineage that is distant from other members of the genus based on the COI and 18S rRNA sequences. This leech species seems to be a specialized fish parasite that could negatively affect farming and wild stocks of Asian Swamp Eel in China.

Morphological and Phylogenetic Analysis of Eustrongylides sp. and Gnathostoma spinigerum Parasitizing the Asian Swamp Eel Monopterusalbus in China.

Nematode infections transmitted to humans by the consumption of wild or cultured eels are increasingly being reported. In the present study, 120 Asian swamp eel, Monopterus albus (Zuiew), individuals collected from China were examined for parasite infections, and 78 larval nematodes were isolated. Morphological and molecular characteristics, including sequence and phylogenetic analysis of the internal transcribed spacer (ITS) and cytochrome c oxidase subunit I (COI) gene regions, were employed to identify these nematodes at the lowest taxonomic level possible. Asian swamp eel was infected with two zoonotic parasite taxa: Gnathostoma spinigerum advanced third-stage larvae, with 6.67% prevalence and mean intensity = 1.25, and Eustrongylides sp. fourth-stage larvae, with 26.67% prevalence and mean intensity = 2.13. These findings evidence the need to enhance public hygiene and food safety awareness toward eel consumption

Growth Patterns and Food Habits of Swamp Eel (Monopterus albus) from the Common Water of the Riau Main Stadium

Swamp eel is one of the freshwater fish that live in the waters around the Riau Main Stadium. This research aims to understand the growth pattern, feeding habit and to determine the type of food present in the fish’s stomach. This research was carried out in September-October 2020. Sampling was conducted five times, once/week, using a fish rod and bamboo fish trap. There were 52 fishes captured (TL 291-613 mm and weight 30-132 gr). The stomach content was analyzed using a volumetric method and the Preponderance Index (PI) of each type of food was calculated. The length-weight relationship shown that the growth of female, intersex and male was negative allometric (b=2.40 in female, b=1,56 in intersex and b= 2,02 in male). Results showed that the food of M. albus in the waters around the Riau Main Stadium consists of insects (PI 49%), fish remains (PI 32%), mollusc (PI 9%), plants (PI 9%) and unidentified materials (1%). Based on data obtained, this fish categorized.

The effect of hydrolysis duration on the antibacterial activity of swamp eel head protein hydrolysate produced by papain against histamine-producing bacteria

Swamp eel (Monopterus albus) processing produced byproducts such as heads that possess a high protein, carbohydrate, lipid, and energies content. Swamp eel heads were hydrolyzed (SEHPH) and tested for their antibacterial activity against histamine-producing bacteria (HPB) to explore the potency. The hydrolysis was conducted by a commercial papain enzyme PAYA (concentration 4%) with various hydrolysis times (0, 60, 120, and 180 minutes) at 60o C with pH 5. The results indicated that increasing hydrolysis time increased solubility and the degree of hydrolysis. The inhibitor concentration 50 test using microdilution of SEHPH inhibited 50% against three HPB named Citrobacter sp. (CK1), Klebsiella sp. (CK13), and Morganella morganii (TK7) at 20 mg/ml. The optimum antibacterial activity test by disk diffusion method was formed by each minute of hydrolysis with the best inhibition zone to Klebsiella sp. (CK13). The macrodillution method showed the highest inhibition was produced by 180 hydrolyses with 45% on CK1, 54% on CK13, and 48% on TK7. These results indicated that SEHPH has potency as an antibacterial agent to reduce histamine-producing bacteria.

IDENTIFIKASI CALON INDUK BELUT SAWAH Monopterus albus (Zuiew, 1793) JANTAN DAN BETINA UNTUK PEMBENIHAN DENGAN MORFOMETRIK TRUSS

Pembenihan belut sawah, Monopterus albus (Zuiew, 1793) belum dapat dilakukan karena terbatasnya teknologi. Pembenihan belut sawah dimulai dengan pemilihan calon induk jantan dan betina dengan mengembangkan metode praktis untuk membedakan jenis kelamin berdasarkan perbedaan morfologi tubuh. Penelitian dilakukan untuk mengidentifikasi perbedaan morfologi belut sawah jantan dan betina dengan metode morfometrik truss. Seratus ekor belut sawah jantan dan betina digunakan dengan mengukur 18 karakter fenotip pada bagian kepala, badan dan ekor. Hasil penelitian menunjukkan terdapat sepuluh karakter fenotip yang dapat digunakan untuk membedakan antara belut sawah jantan dan belut sawah betina. Lima karakter fenotip dapat menunjukkan belut sawah jantan lebih besar ukurannya dibandingkan belut sawah betina terutama pada bagian tubuh anterior nostril, panjang dari ujung depan rahang atas sampai posterior nostril, ukuran lebar mulut, panjang badan dan panjang total. Adapun belut sawah jantan lebih kecil ukurannya dibandingkan belut sawah betina pada panjang dari sudut bukaan mulut sampai belakang pangkal operkulum, panjang rahang atas, panjang kepala, lebar badan bagian vent dan panjang ekor. Secara praktis, bagian ventral-dorsal kepala menjadi penanda belut sawah jantan dengan lebar mulut lebih dalam dan rahang yang lebih kekar. Sedangkan belut sawah betina dapat diketahui dari bagian ekor yang lebih panjang yang diduga berkaitan dengan persiapan rongga untuk perkembangan gonad saat dewasa. Bagian badan tidak dapat dijadikan penanda untuk perbedaan jenis kelamin belut sawah.

Sibship reconstruction with SNPs illuminates the scope of a cryptic invasion of Asian Swamp Eels (Monopterus albus) in Georgia, USA

Cryptic invasive species are particularly problematic to study, manage, and control because of the difficulty detecting these species within their invaded habitats. Such is the case of the Asian Swamp Eel (Monopterus albus; ASE) where it is established in vegetated marshes along the Chattahoochee River, Georgia. Adult eels have been nearly impossible to detect or quantify with traditional sampling, although leaf-litter trapping of juvenile ASEs has been somewhat successful. In this study, we leveraged a collection of juveniles from the 2015 cohort and used single-nucleotide polymorphisms to reconstruct sibship among these juveniles in COLONY. Sibship reconstruction allowed us to learn about adult breeding behaviors and provided the first quantified estimates of breeder abundance. Pedigree reconstruction revealed that adults of both sexes were polygamous and likely traveled up to 0.5 km among marsh habitats during a single breeding season. Estimates of the number of breeding adults contributing to offspring (Ns) and the effective number of breeders (Nb) indicated an approximate minimum bound of 100 breeding adults in the marshes in 2015. Our study updated the invasion status of a cryptic population formerly riddled with uncertainty, highlighting that low captures of adult eels in the study area have been the result of low detectability, not low abundance. Given that low detectability would likely hinder removal efforts, our results suggest that future efforts could focus on suppression of ASE abundance when they are most vulnerable to capture and containing the spatial extent of the invasion.

Ảnh hưởng của hàm lượng protein lên chất lượng nước, tăng trưởng của lươn Monopterus albus (Zwiew, 1793) và cải thìa (Brassica chinensis) trong mô hình aquaponic

The purpose of this study was to examine the effect of different dietary of protein levels on water quality, growth performance of Asian swamp eels Monopterus albus (Zwiew, 1793) and productivity of pak choi (Brassica chinensis) in aquaponic systems. Swamp eels (47.4 g/con) were fed with 4 different dietary protein levels of 25% (NT1), 30% (NT2), 35% (NT3) and 40% (NT 4). The experimental swamp eels were hold in aquaponic recirculting system with pak choi (100 head/m2). The experiment was run for 60 days with two cycles of pak choi. The result showed that higher protein level of feed would induce higher concentration of nitrogen in the form of total ammonia and nitrate. There was a significant difference (P

Growth performance, immunity and intestinal microbiota of swamp eel ( Monopterus albus ) fed a diet supplemented with house fly larvae ( Musca domestica )

Growth performance, immunity and intestinal microbiota of swamp eel ( <i>Monopterus albus</i> ) fed a diet supplemented with house fly larvae ( <i>Musca domestica</i> )

Ontogenetic and Temporal Diet Shifts of the Invasive Asian Swamp Eel in South Florida

AbstractThe Asian Swamp Eel Monopterus albus is an introduced species in South Florida waters and is considered to be a potential threat to the native biota and ecosystems in the region. As a protogynous hermaphrodite that, under the right climatic conditions, can travel short distances over land and tolerate abrupt shifts in salinity, this species has strong invasive potential. In this study, our main goal was to evaluate the potential effects of the Asian Swamp Eel as a predator on native fishes and other biota. Our specific objectives were to (1) analyze the stomach contents of introduced Asian Swamp Eels from canals located near Everglades National Park and (2) assess the ontogenetic and temporal shifts in their consumption of prey. We dissected 752 Asian Swamp Eels (107–833 mm TL), and 46.4% (N = 349) of the samples had stomach contents for the analyses. The analyses indicated that amphipods, fishes, dragonfly nymphs, Hemiptera insects, and grass shrimp Palaemonetes were the most important prey items for Swamp Eels. Swamp Darters Etheostoma fusiforme, juvenile Asian Swamp Eels, and centrarchids were the most common fishes eaten by Swamp Eels. Ontogenetic shifts in diet were apparent, with amphipods and dipteran larvae most often observed in the stomachs of small‐ to medium‐sized Swamp Eels and fish, dragonfly nymphs, and Hemiptera insects more commonly identified in the stomachs of larger eels. The Swamp Eels also became increasingly piscivorous with size. Dragonfly nymphs and grass shrimp occurred more frequently in the Swamp Eel diets in May 2010, while the consumption of fish and amphipods increased in October 2010. Fish were the most important prey item that was consumed during the November–December 2009 period, although other prey items were relatively important during that collection period. As an opportunistic predator that consumes a wide range of prey, the Asian Swamp Eel likely has its greatest effects on native biota and ecosystems as a predator and competitor with native fishes for resources.

Identification and characterization of three CXC chemokines in Asian swamp eel (Monopterus albus) uncovers a third CXCL11_like group in fish

Chemokines direct cell migration in development and immune defense, and bridge between innate and adaptive immune responses. The chemokine gene family has been rapidly evolving and has undergone species/lineage-specific expansion. Mammals possess inflammatory CXC chemokines CXCL1-8/15 and CXCL9-11 sub-groups, and homeostatic CXCL12-14, 16–17. Orthologues of mammalian CXCL12-14, three chemokines related to CXCL1-8/15 (CXCL8_L1-3), two chemokines related to CXC9-11 (CXCL11_L1-2), and five fish-specific chemokines (CXCL_F1-5) have been described in teleosts. In this study, we reported three novel CXC chemokines in Asian swamp eel Monopterus albus, a commercially important freshwater fish species in China. Two of them belong to the fish-specific CXCL_F2 group, named CXCL_F2a/b, that share 89.5% amino acid identity. The other (CXCL11_L3) belongs to a third CXCL11_L related to the mammalian CXCL9-11 subfamily found only in percomorph fish species, and is the only CXCL9-11 related molecules in this lineage. Mammalian CXCL9-11 attract Th1 cells, and block the migration of Th2 cells in an immune response. This study suggests that all major lineages of teleosts have a CXCL9-11 related chemokine that will aid future functional investigation of CXCL11_L in fish. Cxcl_f2a is highly expressed constitutively in the skin of swamp eels that may attract immune cells to protect the skin in the absence of scales. Cxcl11_l3 and cxcl_f2b are highly expressed in immune tissues/organs and are up-regulated by the viral mimic poly I:C, but not bacterial infection in vivo, suggesting their role in anti-viral defense. The two cxcl_f2 paralogues are differentially expressed and modulated, indicating sub- and/or neo-functionalization.

Molecular identification and genetic diversity of Gnathostoma spinigerum larvae in freshwater fishes in southern Lao PDR, Cambodia, and Myanmar.

Gnathostomiasis, an emerging food-borne parasitic zoonosis in Asia, is mainly caused by Gnathostoma spinigerum (Nematoda: Gnathostomatidae). Consumption of raw meat or freshwater fishes in endemic areas is the major risk factor. Throughout Southeast Asia, including Thailand, Lao PDR, Cambodia, and Myanmar, freshwater fish are often consumed raw or undercooked. The risk of this practice for gnathostomiasis infection in Lao PDR, Cambodia, and Myanmar has never been evaluated. Here, we identified larvae of Gnathostoma species contaminating freshwater fishes sold at local markets in these three countries. Public health authorities should advise people living in, or travelling to, these areas to avoid eating raw or undercooked freshwater fishes. Identification of larvae was done using molecular methods: DNA was sequenced from Gnathostoma advanced third-stage larvae recovered from snakehead fishes (Channa striata) and freshwater swamp eels (Monopterus albus). Phylogenetic analysis of a portion of the mitochondrial cytochrome c oxidase subunit I gene showed that the G. spinigerum sequences recovered from southern Lao PDR, Cambodia, and Myanmar samples had high similarity to those of G. spinigerum from China. Sequences of the nuclear ribosomal DNA internal transcribed spacer 2 region closely resembled sequences of G. spinigerum from Thailand, Indonesia, the USA, and central Lao PDR. This is the first molecular evidence of G. spinigerum from freshwater fishes in southern Lao PDR, Cambodia, and Myanmar.

Karyotype diversity and evolutionary trends in the Asian swamp eel Monopterus albus (Synbranchiformes, Synbranchidae): a case of chromosomal speciation?

BackgroundSynbranchidae or swamp eels are fishes belonging to the order Synbranchiformes that occur in both freshwater and occasionally in brackish. They are worldwide distributed in tropical and subtropical rivers of four different continents. A large degree of chromosomal variation has been found in this family, mainly through the use of conventional cytogenetic investigations. Inside this group, a still almost unexplored species under the cytogenetic point of view is the Asian swamp eel Monopterus albus, a widely distributed species throughout Asia. Here, we tested the hypothesis of chromosomal speciation, where a case of sympatric speciation may occur as the primary consequence of chromosomal rearrangements. We performed a comparative chromosomal analysis of M. albus from 22 different localities in Thailand, using distinct staining methods (C-banding, Ag-NO3, and Chromomycin A3), and FISH with repetitive DNA probes (5S rDNA, 18S rDNA, Rex1 element and microsatellite repeats).ResultsThis approach evidenced two contrasting karyotypes (named karyomorphs A and B) that varied concerning their 2n and repetitive DNAs distribution, where chromosomal fusions and pericentric inversions were involved in such differentiation. While the karyomorph A has 2n = 24 chromosomes, the karyomorph B has only 2n = 18, both with NF = 24. In addition, karyomorph A contains only acrocentric chromosomes, while karyomorph B contains three unique metacentric pairs. These features highlight that M. albus has already gone through a significant genomic divergence, and may include at least two cryptic species.ConclusionsThis marked chromosomal differentiation, likely linked to the lifestyle of these fishes, point to the occurrence of a chromosomal speciation scenario, in which fusions and inversions had a prominent role. This highlights the biodiversity of M. albus and justifies its taxonomic revision, since this nominal species may constitute a species complex.

Seasonal variation of heavy metals and metallothionein contents in Asian swamp eels, Monopterus albus (Zuiew, 1793) from Tumpat, Kelantan, Malaysia

BackgroundLevels of toxic metal exposure in indigenous inhabitants are key bioindicators of the severity of environmental contamination. This study measured the seasonal variation of heavy metals and metallothionein (MT) contents in Asian swamp eels (Monopterus albus) from a paddy field situated in Tumpat, Kelantan, Malaysia, to identify prevalence, patterns and associations and togain insight on the suitability of MT as a biomarker for metal exposure.MethodsGill, muscle and liver tissues of M. albus (n = 50) sampled during the ploughing, seedling, growing and harvesting phases of rice growing were collected. The concentrations of copper (Cu), zinc (Zn), lead (Pb), nickel (Ni), and cadmium (Cd) in these tissues were determined by flame atomic absorption spectrometry. MT from each sample was isolated and purified, and subsequently quantitated using UV spectrophotometry. Associations between metal and MT concentrations, season and tissue type were evaluated using Pearson correlation and ANOVA with post-hoc Tukey HSD analysis.ResultsZn was present in higher quantities in gill and liver tissues, while Cu levels were elevated solely in liver. Patterns of non-essential metal accumulation were varied: Cd was detected in low concentrations in all tissues, while Pb and Ni were abundant in gill tissues across all seasons. MT concentration in liver tissue was consistently higher than that found in muscle or gill tissue, except during the growing phase. Moreover, significant correlations (P < 0.05) were observed for Cd, Ni, and Zn when MT was employed as metal exposure biomarker. However, no significant association was found between high Pb and Ni levels and MT concentration in gill tissue.Variation of bioaccumulation rates of heavy metals among the different tissues was observed. Some of these metal concentration differences were found to be associated with MT concentration and, by extension, to its high metal-binding capacity.ConclusionsSignificant liver MT-Zn, MT-Cd, and MT-Ni correlations found in this study emphasised the role of metallothionein as a biomarker for exposure of zinc, cadmium and nickel metals in M. albus.

Effects of Housefly Maggot Meal and Earthworms on Growth and Immunity of the Asian Swamp Eel Monopterus albus (Zuiew)

Fly larvae (maggot meal) and earthworms are promising potential replacements for increasingly expensive and unsustainable fishmeal. Apart from being a good protein source, fly larvae also contain substances with immunostimulant capacity, however the impact of their inclusion in feed on the immune system remains only partially understood. To address this, we studied the effects of four diets with varying levels of earthworm (40-70%) and maggot meal (0-30%) on growth and immunocompetence of juvenile Asian swamp eels Monopterus albus (fish n = 480, duration = 40 days). Maggot meal inclusion resulted in a significantly (P&lt;0.05) higher total protein, glutamic pyruvic transaminase activity, anti-oxidizing enzyme and lysozyme activity, and significantly lower triglycerides, in the blood serum. Bacterial (Aeromonas hydrophila) challenge test results showed that adding maggot meal to the feed improved survival rate and immunocompetence at all three tested inclusion ratios. The strongest positive impact on most studied parameters (including 50% higher survival and 21.4% higher immunocompetence) was observed in the 20% inclusion group. As positive effects were slightly lower at the 30% level, the optimal combination of the two ingredients was 20% maggot meal and 50% earthworms

Effects of different stocking densities on growth performance of Asian swamp eel Monopterus albus, water quality and plant growth of watercress Nasturtium officinale in an aquaponic recirculating system

This study was conducted to determine the effect of different stocking densities on growth rate of Asian swamp eel (Monopterus albus), growth of watercress (Nasturtium officinale) in a floating-draft aquaponic recirculating system. Two factorial experiment designs consist of three different swamp eel (16.67 ± 3.48 g/individual) densities of 100, 180 and 260 individuals/m2 (8.4, 15.0 and 21.7 kg/m3, respectively) integrated with hydroponic trough of watercress (SEW) or without watercress (swamp eel only, SE). Watercress seeds were put into styrofoam, floating rack (80 heads/m2). Swamp eels were fed 2 times per day with commercial pellet (42% protein). The experiment was run for 65 days with two cycles of watercress. Statistical analysis by Two-way ANOVA showed that there is no significant difference (P > .05) in growth performance of swamp eel at different stocking densities between the SEW and SE systems. However, statistical analysis by One way ANOVA showed that there is a significant difference (P < .05) on weight gain (WG) and daily weight gain of animals among the SEW treatments. The highest WG was 32.78 ± 2.09 g/ind. and 41.71 ± 9.05 g/ind. for treatment of 180 inds./m2 at the SEW and SE, respectively. The average survival rate of animal in all treatments was above 80% and was not significant difference among the treatments. The lowest FCR (2.15 ± 0.94) were found in treatment 180 inds./m2 of the SEW. Production of watercress was low in all treatments, the highest biomass (507.81 ± 91.01 g/m2) was recorded for treatment 180 inds./m2 of the SEW. Nutrient accumulation was relatively high at higher stocking densities of swamp eel and was higher in the SE system compared to the SEW system. Total ammonia nitrogen (TAN) concentrations in the SE treatments were ranging from 2.61 ± 1.81 mg/L (120 ind./m2) to 5.77 ± 3.19 mg/L (260 ind./m2). Whereas, the TAN levels in the SEW treatments were only ranging from 1.94 ± 1.44 to 5.35 ± 0.36 mg/L and even lower in hydroponic trough (1.3–3.15 mg/L). Similarly, nitrate‑nitrogen level was high in the SE treatments (1.43 ± 1.36–2.36 ± 1.43 mg/L) and lower in the SEW treatments (0.89 ± 1.36–1.42 ± 1.34 mg/L). Generally, swamp eel farming combined with hydroponic trough was feasible in handling water quality and required little water change in contrast to SE treatments which required as much as 1 water change a day. This study found that the stocking density of 180 inds./m2 seems to be the most effective density for growth, survival of swamp eel as well as nutrient accumulation in the SEW. The results of this study provide an important information as to how aquaculture of swamp eel may be expanded in the Mekong Delta without destroying the environment by releasing nutrient rich effluent from growing chambers.