Swamp Eel Research Articles

A New Endogean, Dwarf, and Troglomorphic Species of Swamp Eel of the Genus Ophisternon (Synbranchiformes: Synbranchidae) from Costa Rica: Evidence from Comparative Mitogenomic and Anatomical Data

A New Endogean, Dwarf, and Troglomorphic Species of Swamp Eel of the Genus Ophisternon (Synbranchiformes: Synbranchidae) from Costa Rica: Evidence from Comparative Mitogenomic and Anatomical Data

Dietary nicotinamide improves growth performance and ameliorates liver lipid profiles by alleviating glycerophospholipid and sphingolipids metabolism in swamp eel (Monopterus albus)

The effect of dietary niacinamide (NAM) on the growth performance and liver lipid metabolism of swamp eel have been poorly investigated. Therefore, a 120-day feeding trial was conducted to provide different levels of NAM in diet and an untargeted lipidome analysis was performed to address this subject. We found that dietary NAM improved the growth performance of swamp eel. It also decreased the contents of glucose and lipids, including glucose, glycogen, TG, and NEFA, as well as fat accumulation in liver, but increased HDL-C content. We speculated that NAM inhibited lipid accumulation in liver by decreasing the key enzyme activity of LPL, HL and LPS. Fatty acid profile analysis showed that the contents of MUFA and PUFA, such as palmitoleic acid, oleic acid, and eicosapentaenoic acid were significantly increased, while the contents of SFA, such as myristic acid, stearic acid, and palmitic acid were decreased in liver by dietary NAM. Lipidome analysis also indicated that the majority of differential lipid metabolites belonged to glycerophospholipids and sphingolipids, which were enriched in the pathways of insulin resistance, adipocytokine signaling pathway, cholesterol metabolism, fat digestion and absorption, lipid and atherosclerosis, and lipid cell lipolysis regulation. These findings gave scientific evidences and novel insights into the metabolic responses to dietary NAM in swamp eel, and provided basic knowledge for using NAM as a feed additive in swamp eel production.

Investigation of Antioxidant Mechanisms of Novel Peptides Derived from Asian Swamp Eel Hydrolysate in Chemical Systems and AAPH-Induced Human Erythrocytes.

Sixteen novel antioxidant peptides from Asian swamp eel (ASE) were identified in previous studies. However, their chemical and cellular antioxidant mechanisms remain unclear. Molecular docking of these peptides with ABTS and DPPH radicals revealed the critical role of hydrogen bonding and Pi-Pi stacking hydrophobic interactions between hydrophobic amino acid residues and free radicals. Residues, such as tryptophan, proline, leucine, and valine, played significant roles in these interactions. All these peptides exhibited notable erythrocyte morphoprotective effects in a model of AAPH-induced oxidative damage of human erythrocytes. Erythrocyte hemolysis was reduced primarily through the modulation of both non-enzymatic (GSH/GSSG) and enzymatic antioxidant systems (SOD, CAT, and GSH-Px) by these peptides. A decrease in levels of MDA, LDH release, and hemoglobin oxidation was observed. Among the peptides, VLYPW demonstrated superior chemical and cellular antioxidant activities, which may be attributed to its higher levels of tyrosine and tryptophan, as well as to its increased hydrophobic amino acid content.

Asian swamp eels (Synbranchidae, Monopterus) in Florida: distribution, spread, and range of hydrologic tolerance over twenty-seven years (1997–2023)

Asian swamp eels (Monopterus albus/javanensis) were first reported as introduced to Florida waterbodies in 1997 near Tampa and Miami; a third population was recorded by 1999 in Homestead. Initial assessments, published soon after swamp eels in southern Florida were first recorded in wetlands beyond canals and ponds (in 2007), concluded there was little threat to Florida’s aquatic ecosystems. Long-term data now suggest they precipitated population crashes of crayfishes and small fishes in the eastern Everglades. We used records from continuous long-term monitoring programs, sporadic monitoring studies, and online databases to reconstruct swamp eel presence across Florida. Monitoring studies provided wetland hydrologic variables to assess limits for swamp eels. From 1997–2007, populations in southern Florida remained restricted to canals; initial spread from 2007–2017 across southern Everglades National Park proceeded slowly and the two populations covered ~1500 km2 of southern Florida. From 2017–2022, the rate of spread increased as they spread west and north (~5800 km2 range). Through 2014, the Tampa population occurred only along southern/eastern Tampa Bay (~60 km2) but has since spread south along the Gulf Coast, east into central Florida, and south along the Lake Wales Ridge (~11,000 km2). We found evidence of two potentially new introductions, in Palm Beach County and Orlando. There was no clear evidence of limitation of wetland drying on swamp eel occurrence in the Everglades; they were captured in marshes that dried for 1–5 months during the previous dry season, but short-hydroperiod wetlands may have slowed spread. In the Everglades, evidence suggests swamp eels may have been inadvertently spread into marshes from canals used to deliver water for flood control and hydrologic restoration. Swamp eels are currently spreading unchecked across Florida, and there should be great concern about continued spread in this region and their establishment and spread elsewhere.

Measurement of Heavy Metal Mercury (Hg) Content in The Swamp Eel (Monopterusalbus) as a Bioindicator from Lake Rawa Taliwang

The presence of heavy metals in Lake Rawa Taliwang can originate from various activities in the upstream river, around settlements, and within the lake itself. Mercury (Hg) is a highly toxic heavy metal due to its neurotoxic nature, affecting both organisms and humans. One of the fish found in Lake Rawa Taliwang is the swamp eel. Swamp eels are often caught for consumption and cultured by the local community. This study aims to determine the mercury (Hg) concentration in swamp eels (Monopterus albus) and assess their suitability for consumption. Sampling was conducted using purposive sampling technique at two stations with two replications at each station. Data analysis involved determining mercury concentration in the swamp eel samples using Atomic Absorption Spectroscopy (AAS). The results showed that the mercury concentration in swamp eels from Lake Rawa Taliwang was 0.13 mg/kg. According to the BPOM regulation no. 9 of 2022, the mercury concentration in these swamp eels is still below the permissible limit for metal contamination in food. This indicates that swamp eels were taken from Lake Rawa Taliwang is safe for consumption.

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.

Effects of polystyrene nanoplastics on apoptosis, digestive enzymes, and intestinal histological structure and flora of swamp eel (Monopterus albus)

After the swamp eel (Monopterus albus) was exposed to NPs, it showed inflammation in the liver and intestine, significant changes to genes in the liver, and an increase in the abundance of pathogenic bacterial populations in the intestine.

LPXRFa and LPXRFa-R in the female swamp eel (Monopterus albus): Molecular cloning, tissue distribution and gonadal function

Gonadotropin-inhibitory hormone (GnIH) is a hypothalamic neuropeptide known for inhibiting gonadotropin release. In teleosts, it is also referred to as LPXRFa. While the effects of LPXRFa on gonadotropin synthesis and release, and its impact on pituitary function in teleosts have been widely studied, its specific mechanism in fish reproduction remains relatively unexplored. In this paper, LPXRFa and LPXRFa-R genes were isolated from the swamp eel brain to assess the roles of LPXRFa in the swamp eel. Their ORFs were 612 bp and 1284 bp, encoding proteins of 203 and 427 amino acids, respectively. The LPXRFa gene encodes a polypeptide possibly cleaved into three mature peptides (LPXRFa-1, −2, and −3). The LPXRFa-R receptor protein comprises seven conserved transmembrane domains. Tissue distribution analysis revealed that LPXRFa-R expression was the highest in the hypothalamus, while LPXRFa showed the highest expression in the rest of brain, with little to no expression in other tissues. The role of LPXRFa in the reproduction of the swamp eel was investigated by studying the effect of intraperitoneal injection with each of the three peptides. The intraperitoneal injection of LPXRFa-2 down-regulated serum FSH and LH levels, while that of LPXRFa-3 down-regulated serum FSH but up-regulated LH levels. Additionally, both LPXRFa-2 and LPXRFa-3 increased the expression levels of fshr, cbx3, dmrt1, gsdf, sox9al, amh, foxl2, and rab37 in the ovaries. Moreover, LPXRFa-2 also increased the ovarian expression of lhr, while LPXRFa-3 had no effect on it. Except upregulating cbx3 and foxl2 expression, LPXRFa-1 neither impacted the serum FSH and LH levels, nor did it alter the expression of other gonadal and reproductive-related genes. In summary, our findings provide the first evidence of a LPXRFa/LPXRFa-R system in the order Synbranchiformes and suggest its involvement in sex differentiation, gonadal development, and sexual reversal in the swamp 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.

Caring for Waterscapes in the Anthropocene: Heritage-making at Budj Bim, Victoria, Australia

Abstract Australian waterscapes were fashioned to meet human needs during the ancient Aboriginal past through the construction of weirs, fish traps and small dams and accompanying socio-cultural practices and institutions. Exemplary amongst Australian water cultures was that of the Gunditjmara of western Victoria, who for thousands of years practiced a sophisticated form of swamp engineering and eel farming in the volcanic landscapes of Budj Bim. Within 150 years of European colonisation, frontier violence, dispossession and hydrological alteration had put an end to the most extensive and oldest aquaculture system in the world. Recent land and water restitution measures enacted in collaborative partnerships with the wider watershed community have enabled the Gunditjmara to restore the Budj Bim wetlands and rebuild their nation. This process entails re-storying engineering and eeling: cultural practices and connections are being retold to gain recognition for the capacity to negotiate change and adapt to geological, climatological and imperial forces. Critical theory and concepts relating to waterscapes, hydro-social relations and the Anthropocene assist in interpreting the resilient efforts of a rural community to retrieve its history and find new ways to care for the past as well as the future.

Study on efficient metabolism mechanism of starch in the intestine of carnivorous fish: A case of Monopterus albus

An efficient metabolism of mammals in the intestine is a crucial factor in their dietary starch utilization. Swamp eel (Monopterus albus), a carnivorous fish, has shown a remarkable ability to utilize dietary starch efficiently. However, the specific mechanisms underlying this efficient starch metabolism in the intestine remain poorly understood. Thus, we conducted a study in which juvenile swamp eels (average weight: 12.10 ± 0.03 g) were fed diets with two different starch levels (20 % -NF and 32 % -HF) for a period of 56 days. Subsequently, the intestine and digesta were extracted for analysis. This study showed that there was no significant variety on the activity of digestive enzyme and histological structure in anterior intestine of fish between HF group and NF group. However, HF diets down-regulated the expression of all differentially expressed genes of glycine--tRNA ligase concerned to damage in the most significantly enriched GO function of glycyl-tRNA aminoacylation. Besides, the HF diets significantly increased the genus of Cetobacterium with the function of producing acetic acid. Consistently, the HF diets significantly increased the concentration of short chain fatty acids (SCFA), particularly acetic acid, in the posterior intestine digesta of swamp eel. In summary, our study argued that the enhanced efficiency in utilizing dietary starch by the swamp eel might be attributed to the increased abundance of Cetobacterium and the subsequent production of acetic acid in the posterior intestine.

Asian Swamp Eel, Monopterus javanensis (La Cepède 1800), as natural prey for the Malayan Krait, Bungarus candidus (Linnaeus 1758), in Narathiwat Province, southern Thailand

Asian Swamp Eel, Monopterus javanensis (La Cepède 1800), as natural prey for the Malayan Krait, Bungarus candidus (Linnaeus 1758), in Narathiwat Province, southern Thailand

Disruption of intestinal structure, tight junction complex, immune response and microbiota after chronic exposure to copper in swamp eel (Monopterus albus)

As an essential micronutrient, copper is crucial in aquatic organisms' growth and development. Numerous studies have consistently reported that excessive intake of copper can have harmful effects on organisms. However, there are limited studies on the impact of copper on the intestine of the swamp eel (Monopterus albus). This study aimed to investigate the changes of intestinal histopathology, tight junction complex, immune response, and microbiota in swamp eel treated with 0 mg/L Cu2+, 0.05 mg/L Cu2+, and 0.10 mg/L Cu2+ for 56 d. Intestinal histopathology showed major changes such as the increased number of erythrocytes and goblet cells in the lamina propria, and separation of the lamina propria. The expression of genes involved in tight junction complex (ZO-1, Claudin-3, Claudin-12 and Claudin-15) was significantly changed. In addition, copper exposure significantly increased the mRNA levels of TLR3, TLR7, TLR8, NF-κB, I-κB, TNF-α and IL-8, especially in 0.10 mg/L Cu2+ group. In contrast, the relative expression level of anti-inflammatory cytokine TGF-β was significantly decreased after exposure to copper. Analysis of the intestinal microbiome showed the intestinal microbiota of swamp eels in the control and copper exposure groups were dominated by Firmicutes and Proteobacteria at the phylum level. Notably, copper exposure changed the diversity of the intestinal microbiota and decreased the relative abundance of Firmicutes and Proteobacteria in the intestine of swamp eel. Collectively, this study demonstrates that chronic copper exposure induces intestinal pathologic changes and inflammatory response, disrupts the intestinal microbial diversity and microbiota composition, and decreases intestinal barrier function in swamp eel, which enhances our understanding of copper-induced intestinal toxicity in fish.

Effects of dietary arachidonic acid on growth, gonadal development, and tissue fatty acid composition in the hermaphroditic swamp eel (Monopterus albus)

10-week dietary arachidonic acid (ARA) feeding trials were conducted in 14-month-old swamp eel (Monopterus albus) to evaluate the effects on growth performance, gonadal development, tissue fatty acid profile, and gene expression related to lipid metabolism. The results showed that swamp eels fed diets supplemented with 1.4% or 2.8% ARA had a significantly higher weight gain rate (WGR) and specific growth rate (SGR) than those fed the control diet. Dietary supplementation with ARA improved oocyte development and maturation. Higher gonadosomatic index (GSI) was detected in 1.4% and 2.8% ARA groups. ARA supplementation delayed sexual reversal in females. The ARA content in the muscle, liver and gonads increased with increasing dietary ARA concentration; however, ARA supplementation significantly reduced the transcriptional expression of lipid metabolism-related genes in the gonads, such as fad2, pla2g4a, and elovl5. Serum alanine aminotransferase (ALT) levels in the ARA 1.4% group were significantly lower than those in the control and ARA 2.8% groups. Total cholesterol (T-CHO) and triglyceride (TG) levels were significantly lower in the 1.4% and 2.8% ARA groups than in the control group. Catalase (CAT) and high-density lipoprotein cholesterol (HDL-C) increased with dietary ARA concentrations. This study found that dietary ARA is important for improving growth, Ovarian development, and antioxidant capacity in swamp eels.

Ecological Significance of Monopterus cuchia in the Budhi Ganga Ecosystem of Hastinapur: A Multifaceted Exploration

This study delves into the profound ecological implications of Monopterus cuchia, commonly referred to as the Indian swamp eel, within the revered confines of Hastinapur, an ancient capital of the Mahabharata era, and the intricate Budhi Ganga ecosystem. We explore the remarkable adaptations of M. cuchia to oxygen-depleted swamp environments, primarily through the intricate mechanism of cutaneous respiration, bridging the domains of historical reverence and ecological inquiry. The Budhi Ganga, characterized by its rich historical, cultural, and ecological significance, reveals itself as a repository of intricate biodiversity complexities. Monopterus cuchia, occupying crucial ecological niches both as a predator and prey, orchestrates trophic intricacies that reverberate throughout the riverine food web. In parallel, these eels take on the role of astute ecological indicators, poised to signal shifts in water quality, habitat stability, and nutrient dynamics. Nonetheless, the delicate equilibrium of the Budhi Ganga faces imminent peril from anthropogenic intrusions, particularly the allocation of land along its revered banks. These disruptions manifest as habitat degradation, hydrological perturbations, and insidious pollutant intrusions, leading to a regrettable decline in ecological diversity. The urgency of safeguarding the ecological sanctity of the Budhi Ganga transcends conventional ecological stewardship, encompassing profound cultural and historical responsibilities. This research emphasizes the critical need for rigorous conservation paradigms, comprehensive ecosystem restoration initiatives, and prudent land management protocols to navigate the intricacies of these complex ecosystems.

Identification of potential indicators for testis quality in swamp eels (Monopterus albus) through metabolomics analysis

The swamp eel (Monopterus albus) is a commonly cultured freshwater fish. Selection and cultivation of fecund broodstock is crucial for efficient artificial reproduction in this species. However, there are currently no guidelines for selecting high-quality males in M. albus. This study quantitatively investigated the sperm motility of male swamp eels during the breeding season by using computer-assisted sperm analysis system. Variability in the proportion and number of motile sperm was observed between individual males. The testes were grouped into high-quality and low-quality according to sperm quality. Morphometric parameters of the two groups were analyzed. We found that high-quality testes were longer (150 ​± ​27 ​mm verses 127 ​± ​19 ​mm) than low-quality testes. Besides, the proportion of testes with a dark appearance was slightly higher (58.3% verses 48.1%) in the high-quality group than in the low-quality group. Metabolomic analysis was conducted to compare the metabolite profiles of high-quality and low-quality testes. Glycerophospholipids, organic acids, glycerolipids, amino acids, sphingolipids, and nucleotides were the most abundant metabolites in the testes of swamp eels. Moreover, 135 differential metabolites were identified. Several nucleotide derivatives, including 5′-deoxyadenosine, 2′-deoxyadenosine, and ribosyl adenosine, were the most significantly enriched metabolites in high-quality testes. These metabolites are potential indicators for the testis quality in M. albus. Altogether, our work provides systematic and quantitative data about the physiological and biochemical characteristics of M. albus testis, which provides an evidential basis for the selection of high-fecundity parents to improve artificial reproduction efficiency of M. albus.

Effect of spray drying parameters on the physicochemical properties and oxidative stability of oil from menhaden (Brevoortia spp.) and Asian swamp eel (Monopterus albus) oil extract microcapsules

This work investigated the effect of spray drying parameters on the physicochemical properties and oxidative stability of oil from menhaden (Brevoortia spp.) and Asian swamp eel (Monopterus albus) oil microcapsules. Different emulsion formulations (Maltodextrin - MD, Maltodextrin+Gum Arabic - MD+GA, and Maltodextrin+Starch - M+S), inlet air temperatures (180, 190, and 200 °C), and feed flow rates (280, 382, and 485 mL/h) were applied to microencapsulate Brevoortia spp. oil. The best operating parameters were then used to microencapsulate the Monopterus albus oil. The moisture content, MC (%), peroxide value, PV (mEq/kg), free fatty acid, FFA (%), acid value, AV (mg KOH/g) and the morphology of the microcapsules were then evaluated. The Brevoortia spp. oil microcapsules produced with the Maltodextrin+Gum Arabic emulsion formulation, inlet air temperature of 200 °C, and feed flow rate of 280 mL/h showed the lowest moisture content, peroxide value, free fatty acid, and acid value of 9.145%, 3.293 mEq/kg, 4.891%, and 2.981 mg KOH/g, respectively. Using similar parameters, the microencapsulation of the Monopterus albus oil extract recorded a moisture content, peroxide value, free fatty acid, and acid value of 8.432%, 2.713 mEq/kg, 4.911%, and 2.871 mg KOH/g, respectively. In conclusion, improved physicochemical properties and oxidative stability of Monopterus albus oil extract microcapsules were achieved using the Maltodextrin+Gum Arabic emulsion formulation and spray drying at a high air inlet temperature of 200 °C and a low feed flow rate of 280 mL/h.

First report of a histozoic Henneguya (Cnidaria, Endocnidozoa) infecting a synbranchid potamodromous fish from South America: Morphostructural and biological data

In this study, a Henneguya myxosporean species is described to infect an ecological, biological, and evolutionary important fish from Amazon biome. The myxosporean was found in the skin of only one specimen of marbled swamp eel, Synbranchus marmoratus caught in a small stream from Peruvian Amazon floodplain. Mature myxospores have ovoid shape from the valvular view, measuring 32.2 ± 0.6 μm (31.6–32.8) in total length, 21.5 ± 0.3 μm (21.2–21.8) in spore body length, 11.7 ± 0.5 μm (11.2–12.2) in width and 10.6 ± 0.9 μm (9.7–11.5) in thickness. Non-bifurcate caudal appendage, measuring 10.7 ± 0.4 μm (10.3–11.1) in length. Two polar capsules elongated aubergine in shape, equal in size and measuring 4.9 ± 0.2 μm (4.7–5.1) in length and 3.1 ± 0.5 μm (2.6–3.6) in width. Polar tubules coiled in 7–8 turns. This is the first report of a Henneguya species parasitizing a fish of the order Synbranchiformes from Amazon basin and the first to describe this parasite infecting a potamodromous fish from South America.

Stimulator of interferon genes from Asian swamp eel (MaSTING) is involved in host defense against bacterial infection.

Stimulator of interferon genes (STING) is an endoplasmic reticulum (ER)-associated protein that plays critical roles in innate immunity and pathogenesis of various diseases. To date, teleost STING against viral stimulation has been identified, whereas STING signaling events in fish against bacteria are not well understood. In the present study, the open reading frame (ORF) of STING from Asian swamp eel (Monopterus albus) was cloned (named MaSTING) and its roles in bacterial infection were investigated. Amino acid sequence alignment and phylogenetic analysis revealed that MaSTING had conserved structures with mammalian STING and shared the closest relationship with mandarin fish STING. Subcellular localization analysis showed that MaSTING distributed in the whole cytoplasm and mainly co-localized with ER. Expression pattern analysis found that MaSTING was constitutively expressed in all the examined tissues with the highest expression in the liver and spleen. Post stimulation with bacteria and various PAMPs, the expression of MaSTING was induced at indicated time points in the immune-related organs and isolated peripheral blood leucocytes. Furthermore, the mechanism underlying MaSTING against bacterial infection was further studied. The qPCR analysis showed that MaSTING overexpression promoted 2'3'-cGAMP induced the expression of IFN-1, ISG15, Viperin, Mx, IL-1β and TNF-α. Western blotting assay suggested that MaSTING significantly enhanced the phosphorylation of TANK-binding kinase 1 (TBK1) and p65. MaSTING also significantly increased the luciferase activity of IFN-1 and NF-κB promoters. Taken together, MaSTING is involved in host defense against bacterial infection by inducing the inflammatory response.

Insights into the mechanism of growth and fat deposition by feeding different levels of lipid provided by transcriptome analysis of swamp eel (Monopterus albus, Zuiew 1793) liver.

Lipid is an important source of energy in fish feeds, and the appropriate fat content can improve the efficiency of protein utilization. However, excessive lipid content in the feed can lead to abnormal fat deposition in fish, which has a negative effect on the growth of fish. Therefore, the effects of feed lipid levels on swamp eel were studied. Essential functional genes were screened using transcriptomics. We divided 840 fish into seven groups (four replicates). A mixture of fish and soybean oils (1:4), 0%, 2%, 4%, 6%, 8%, 10%, and 12% was added to the basic feed were named groups one to seven (L1-L7), respectively. Isonitrogenous diets were fed swamp eel for 10 weeks. Growth performance, visceral index, nutritional components, and biochemical indexes were measured and analyzed. Livers of the 0%, 6%, and 12% groups were subjected to transcriptome sequencing analysis. The results of our study showed that: the suitable lipid level for the growth of swamp eel was 7.03%; the crude fat content of whole fish, liver, intestine, muscle, and skin increased with the increase of lipid level, with some significant difference, and excess fat was deposited in skin tissue; triglyceride, total cholesterol, and free fatty acid contents increased with the increase of feed lipid level. High-density lipoprotein levels in the L3 and L4 groups were higher than in the other groups. Blood glucose concentrations in the L5, L6, and L7 groups increased; the liver tissue structure was damaged when the lipid level was too high. two-hundred-and-twenty-eight differentially expressed genes were found. Several critical pathways regulating glucose metabolism and energy balance (e.g., glycerolipid metabolism, glycolysis synthesis, degradation of ketone bodies, and Janus Kinase/Signal Transducer and Activator of Transcription signaling pathway) were enriched in swamp eel compared with the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. Suitable lipid levels (7.03%) can promote the growth of swamp eel, and excessive lipid levels can cause elevated blood lipids and lead to liver cell damage. Regulatory mechanisms may involve multiple metabolic pathways for glucose and lipid metabolism in eels. This study provides new insights to explain the mechanism of fat deposition due to high levels of lipid and provides a basis for the production of efficient and environmentally friendly feed for swamp eel.