Search Results (16)

Histamine is a significant risk factor in brown fishmeal and negatively affects histamine-sensitive fish species. The present study aimed to explore the potential protective effects of dietary sanguinarine supplementation against the adverse impacts of excessive dietary histamine on growth and intestinal and hepatic health in American eels. Four experimental diets were formulated: the basal diet (control diet), the basal diet supplemented with 500 mg kg⁻¹ of histamine (HH diet), and the HH diet supplemented with 100 mg kg⁻¹ and 200 mg kg⁻¹ of sanguinarine (HH+SAN100 and HH+SAN200 diets, respectively). After a 10-week feeding trial, both sanguinarine supplementation diets alleviated HH-diet-induced growth retardation, reduced feed utilization, serum dyslipidemia, and hepatic and intestinal structural damage; decreased hepatic and intestinal antioxidant capacity; increased intestinal and hepatic malondialdehyde levels; inhibited intestinal lipase activities; elevated intestinal pro-inflammatory-related gene abundance; and lowered intestinal anti-inflammatory-related gene expression. Furthermore, the HH+SAN100 diet partially ameliorated HH-diet-induced gut microbiota dysbiosis and intestinal metabolic disturbances. Collectively, these findings identify sanguinarine as a functional dietary additive that mitigates histamine-associated growth suppression and intestinal and hepatic injury in American eels, promoting the sustainable utilization of brown fishmeal in American eel culture. Full article

This study was performed to explore the influences of dietary peanut skin proanthocyanidins (PSPcs) on the antioxidant capability and intestinal health of juvenile American eels (Anguilla rostrata). The American eels (10.50 ± 0.03 g) were randomly allocated to five groups. Five experimental diets were formulated with graded levels of PSPc supplementation, and designated as PSPc0, PSPc300, PSPc600, PSPc900, and PSPc1200, respectively. The feeding experiment lasted for 8 weeks. In comparison with the PSPc0 group, the PSPc supplementation groups exhibited higher total antioxidant capacity and elevated levels of reduced glutathione, along with increased activities of superoxide dismutase, catalase, glutathione peroxidase, and glutathione S-transferase in the serum, liver, and intestine (p < 0.05). Dietary PSPc supplementation significantly decreased malondialdehyde levels in the serum, liver, and intestine (p < 0.05) and down-regulated hydrogen peroxide and nitric oxide levels in the liver and intestine (p < 0.05). Dietary PSPc supplementation also enhanced hepatic and intestinal anti-free radical superoxide anion and anti-free radical hydroxyl capacities (p < 0.05). Most of these parameters peaked in the PSPc900 group. PSPc supplementation in the diet increased villus height and muscular thickness and elevated activities of intestinal lipase and protease (p < 0.05), with lipase activity being the highest in the PSPc900 group. Compared with the PSPc900 group, the above-mentioned parameters in the PSPc1200 group showed a negative effect. Relative to the PSPc0 group, the PSPc900 group exhibited an increased relative abundance of Xanthomonadaceae and reduced relative abundances of Citrobacter, Chroococcidiopsis, Escherichia Shigella, Cupriavidus, Pelomonas, and Romboutsia (p < 0.05). Taken together, appropriate dietary PSPc supplementation improves antioxidant capacity and intestinal health in American eels, and the optimal dietary supplementation level is recommended at 900 mg/kg. Full article

Micro-minerals are essential for fish, but traditional inorganic micro-minerals (IMM) have low bioavailability. This study evaluated coated inorganic micro-minerals (CIMM) in juvenile American eels under commercial recirculating aquaculture system (RAS) conditions. Three experimental groups (n = 3 tanks per group, stocking density: 138 fish/m³) were fed basal diets supplemented for 56 days with: 1000 mg/kg IMM (IMM group, providing Cu 7, Fe 200, Mn 30, Zn 70, I 1.6, Se 0.4, and Co 1.2 mg/kg diet), 1000 mg/kg CIMM (CIMM group I), or 500 mg/kg CIMM (CIMM group II). Compared to the IMM group, the CIMM group I demonstrated significantly enhanced growth performance, with the specific growth rate increasing by approximately 31.14%, higher whole-body content and retention of minerals (Ca, P, Cu, Fe, Mn, Zn), and superior intestinal health, as reflected by significantly increased activities of digestive enzymes (amylase and lipase), enhanced antioxidant capacity (elevated SOD and CAT, reduced MDA), and improved morphology (villi length and muscular thickness), an altered intestinal microbiota (increased relative abundance of Firmicutes and reduced relative abundance of Proteobacteria), and significant metabolomic alterations in purine metabolism and linoleic acid metabolism. The CIMM group II maintained growth performance, with no significant difference in WGR and SGR compared to the IMM group, while still showing significant improvements in feed intake and mineral retention (P, Cu, Fe, Zn), and antioxidant capacity. Collectively, this study not only confirms the efficacy of CIMM in commercial RAS but also reveals that the supplementation level previously shown to be effective in the laboratory (50% CIMM) is insufficient under commercial farming conditions, implying that the dietary micro-mineral requirements for juvenile American eels in commercial RAS may be higher than those established in laboratory settings. Full article

Background: Aeromonas hydrophila is a common bacterial pathogen that causes hemorrhagic septicaemia in several farmed aquaculture species. Phage therapy is considered a promising and feasible alternative to antibiotic treatment. Methods: In this study, an A. hydrophila-infecting jumbo phage Z90 was isolated from an aquaculture pond. The biological characteristics, genomic features, and in vitro and in vivo experiments were investigated to evaluate its application potential. Results: Phage Z90 was a myovirus with distinctive curled tail fibers. Additionally, phylogenetic and genomic analyses found that the phage Z90 was a novel virus belonging to the genus Ferozepurvirus of the family Chimalliviridae. One-step growth curve analysis revealed that the phage Z90 was a lytic phage, exhibiting a short latency period of 20 min and a relatively large burst size of 270 ± 42 PFU/cell. The phage Z90 particles were stable at psychrotrophic and mesophilic temperatures (10–50 °C) and a wide range of pH (pH 3–12). Genomic analysis revealed that the phage Z90 did not contain any genes encoding toxins, virulence factors, or antibiotic resistance factors. In vivo analysis demonstrated that the phage Z90 protected American eels from A. hydrophila infection, greatly increasing eel survival rates and alleviating symptoms caused by bacterial infections. The comparison of different phage administration methods suggested that phage Z90 was better administered through intraperitoneal injection than immersion in aquaculture water. Moreover, the combination of phage Z90 and ampicillin improved the bactericidal effect and reduced the treatment dosage compared to antibiotics or phage alone. Conclusions: Altogether, the findings of this study indicate that the phage Z90 can serve as a promising biocontrol agent for the treatment of A. hydrophila infection in aquaculture. Full article

Vibrio harveyi (Vh) and Vibrio vulnificus (Vv) are major bacterial pathogens affecting farmed eels, but their comparative virulence mechanisms remain poorly characterized. This study combined histopathology and transcriptomic profiling to investigate organ-specific damage and host responses in American eels (Anguilla rostrata, 20 g per fish, for a total of 60 fish) following experimental infection with LD₅₀ doses of Vh (strain HA_1, 7.5 × 10⁴ CFU/fish) and Vv (strain FJ_4, 5.0 × 10⁵ CFU/fish). Tissue samples from liver, kidney, and spleen were collected at 0, 36, and 60 h post-infection (hpi). Histopathological analysis revealed distinct injury patterns: Vh induced severe hepatic edema and necrosis, whereas Vv caused vacuolar degeneration and vascular congestion in the liver. In the kidney, Vv triggered acute necrosis and vacuolization by 36 hpi, while Vh-induced renal damage was delayed until 60 hpi. Transcriptomic analysis of spleen tissue identified 4779 and 1215 differentially expressed genes (DEGs) in the Vh_36 vs. Vv_36 and Vh_60 vs. Vv_60 comparisons, respectively. Functional enrichment analysis associated these DEGs with 109 Gene Ontology (GO) terms—mainly catalytic activity, biological regulation, and binding—and 51 KEGG pathways, including “tuberculosis” and “pathways in cancer”. Differential alternative splicing (DAS) analysis further uncovered 1579 and 1214 DAS events originating from 12,482 and 12,316 splicing genes in the two comparisons. These were enriched in GO categories such as “binding”, “cellular process”, and “cell part”, as well as KEGG pathways related to “signal transduction”, “infectious diseases”, and “immune system.” Protein–protein interaction network analysis identified 119 cross-DAS-encoded proteins, including 8 that were predicted as key regulators of virulence differences. In summary, this work presents the first integrative study comparing the pathogenicity and host transcriptional dynamics of Vh and Vv in American eels, providing new molecular insights into their distinct virulence strategies. Full article

The enzymatic hydrolysis of soybeans could enhance their application as an ingredient and alternative to fishmeal in aquafeeds. Here, a 10-week feeding trial was conducted to evaluate the impacts of different dietary inclusion levels of enzymatically hydrolyzed compound soy protein (EHCS) on the growth performance and intestinal health of juvenile American eels (Anguilla rostrata). Five experimental diets were formulated with graded EHCS inclusion levels at 0% (EHCS0), 8% (EHCS8), 16% (EHCS16), 24% (EHCS24), and 32% (EHCS32). Each diet was randomly assigned to four replicate tanks. The results showed that eels fed the EHCS8 diet exhibited superior growth performance, decreased serum lipid content, and increased immunity compared to those fed the EHCS0 diet. Eels fed the EHCS8 diet also displayed improved intestinal histology, enhanced antioxidant capacity and balance of intestinal microbiota as well as an enhanced proliferation of probiotics compared to those receiving the EHCS0 diet. Compared with eels fed the EHCS0 diet, those fed the EHCS16 diet exhibited comparable growth performance and values for the aforementioned markers. The quadratic regression analysis of weight gain rate and feed efficiency against the dietary EHCS inclusion levels determined the maximum levels of dietary EHCS inclusion for American eels range from 17.59% to 17.77%. Full article

The European eel (Anguilla anguilla (L.)) is a unique catadromous euryhaline fish and the only anguillid eel species classified as ‘critically endangered’. The Baltic Lakeland area contains naturally recruited and introduced eels. There is great uncertainty regarding a baseline for the location and number of naturally dispersed eels in the region. Little is known about the genetic structure of the European eel populations in Baltic countries. The estimation of population genetic structure is important for the efficient management of naturally recruited and introduced eels. Two mitochondrial regions were used to investigate the genetic structure within and between eel samples from 11 waterbodies. In this study, new, unique, and widely distributed haplotypes were revealed. The studied eel population in the Baltic Lakeland shows high genetic diversity, which is possibly a result of intensive restocking programs. Sequences characterized for Anguilla rostrata were revealed in both mitochondrial regions. Understanding the genetic structure of eel populations worldwide is crucial for conservation efforts. Eel restocking in waterbodies where natural migration is restricted contributes to diversity loss for the world gene pool of eels. Full article

With a reduced supply and increased price of white fish meal (WFM), the exploration of a practical strategy to replace WFM is urgent for sustainable eel culture. A 70-day feeding trial was conducted to evaluate the effects of replacing WFM with low-quality brown fish meal (LQBFM) with compound additives (CAs) on the growth performance and intestinal health of juvenile American eels (Anguilla rostrata). The 300 fish (11.02 ± 0.02 g/fish) were randomly distributed in triplicate to four groups (control group, LQBFM20+CAs group, LQBFM30+CAs group and LQBFM40+CAs group). They were fed the diets with LQBFM replacing WFM at 0, 20%, 30% and 40%, respectively. The CAs were a mixture of Macleaya cordata extract, grape seed proanthocyanidins and compound acidifiers; its level in the diets of the trial groups was 0.50%. No significant differences were found in the growth performance between the control and LQBFM20+CAs groups (p > 0.05), whereas those values were significantly decreased in LQBFM30+CAs and LQBFM40+CAs groups (p < 0.05). Compared to the control group, the activity of glutamic-pyruvic transaminase was significantly increased in LQBFM30+CAs and LQBFM40+CAs groups, while lysozyme activity and complement 3 level were significantly decreased in those two groups (p < 0.05). There were decreased antioxidant potential and intestinal morphological indexes in the LQBFM30+CAs and LQBFM40+CAs groups, and no significant differences in those parameters were observed between the control group and LQBFM20+CAs group (p > 0.05). The intestinal microbiota at the phylum level or genus level was beneficially regulated in the LQBFM20+CAs group; similar results were not shown in the LQBFM40+CAs group. In conclusion, with 0.50% CA supplementation in the diet, LQBFM could replace 20% of WFM without detrimental effects on the growth and intestinal health of juvenile American eels and replacing 30% and 40%WFM with LQBFM might exert negative effects on this fish species. Full article

This study was conducted to evaluate the oligomeric proanthocyanidins (OPC) in alleviating the detrimental effects of intestinal health caused by dietary histamine in juvenile American eels (Anguilla rostrata). A total of 480 fish with a similar body weight of 10.84 ± 0.16 g were randomly divided into four groups, and there were the control group fed a basal diet, the HIS group fed a diet with a high level of histamine (534 mg/kg), the H + OPC I group fed the high histamine diet with 300 mg/kg OPC, and the H + OPC II group fed the high histamine diet with 600 mg/kg OPC, respectiviely. After the fish were fed the trial diets for 77 days, the intestinal samples were taken, and the related parameters of intestinal health were analyzed. Dietary 300 mg/kg or 600 mg/kg OPC could reverse the decreased activities of lipase, protease, and glutathione peroxidase and the level of total antioxidant capacity, the increased intestinal malondialdehyde and D-lactate acid levels and the activity of diamine oxidase in serum, and the decreased villus height caused by a high level of dietary histamine. There were no significant differences above all the indices between the H + OPC I group and the H + OPC II group. The higher relative abundances of potentially pathogenic bacteria were induced by the high level of dietary histamine. Dietary 300 mg/kg OPC might increase the relative abundance of the potential probiotics and inhibit the colonization of intestinal pathogenic bacteria of juvenile American eels exposed to the stress of high dietary hisatamine. The intestinal health status of the H + OPC groups was similar to that of the control group. These results suggested that dietary 300 mg/kg OPC might alleviate the detrimental effects of dietary 534 mg/kg histamine on the intestine health of juvenile American eels by increasing the activity of digestive enzymes, improving the antioxidative potential and barrier function, and beneficially modulating the intestinal microbiota. Dietary 600 mg/kg OPC could not exert further improvement in growth performance and the intestinal health of juvenile American eels. Full article

This study was conducted to evaluate the effects of replacing fish meal (FM) with methanotroph (Methylococcus capsulatus, Bath) bacteria protein (MBP) in the diets of the juvenile American eel (Anguilla rostrata). Trial fish were randomly divided into the MBP0 group, MBP6 group, MBP12 group, and MBP18 group fed the diets with MBP replacing FM at levels of 0, 6%, 12%, and 18%, respectively. The trial lasted for ten weeks. There were no significant differences in weight gain or feed utilization among the MBP0, MBP6, and MBP12 groups (except for the feeding rate in the MBP12 group). Compared with the MBP0 group, the D-lactate level and diamine oxidase activity in the serum were significantly elevated in the MBP12 and MBP18 groups. In terms of non-specific immunity parameters in serum, the alkaline phosphatase activity was significantly decreased in the MBP18 group, and the complement 3 level was significantly elevated in the MBP12 and MBP18 groups. The activities of lipase and protease in the intestine were significantly decreased in the MBP12 and MBP18 groups. Compared with the MBP0 group, the total antioxidant capacity and activities of superoxide dismutase, catalase, and glutathione peroxidase in the intestine were significantly decreased in the MBP18 group, while the malondialdehyde level was significantly increased. The villus height, muscular thickness, and microvillus density were significantly decreased in the MBP12 and MBP18 groups. There were no significant differences in the foresaid parameters between the MBP0 group and the MBP6 group. The intestinal microbiota of the MBP6 group was beneficially regulated to maintain similar growth and health status with the MBP0 group. The adverse effects on the intestinal microbiota were reflected in the MBP18 group. In conclusion, MBP could successfully replace 6% of FM in the diet without adversely affecting the growth performance, serum biochemical parameters, and intestinal health of juvenile American eels. Full article

Anguillid herpesvirus 1 (AngHV-1) is a pathogen that causes hemorrhagic disease in various farmed and wild freshwater eel species, resulting in significant economic losses. Although AngHV-1 has been detected in the American eel (Anguilla rostrata), its pathogenicity has not been well characterized. In this study, an AngHV-1 isolate, tentatively named AngHV-1-FC, was isolated from diseased American eels with similar symptoms as those observed in AngHV-1-infected European eels and Japanese eels. AngHV-1-FC induced severe cytopathic effects in the European eel spleen cell line (EES), and numerous concentric circular virions were observed in the infected EES cells by transmission electron microscopy. Moreover, AngHV-1-FC caused the same symptoms as the naturally diseased European eels and Japanese eels through experimental infection, resulting in a 100% morbidity rate and 13.3% mortality rate. The whole genome sequence analyses showed that the average nucleotide identity value between AngHV-1-FC and other AngHV-1 isolates ranged from 99.28% to 99.55%. However, phylogenetic analysis revealed that there was a genetic divergence between AngHV-1-FC and other AngHV-1 isolates, suggesting that AngHV-1-FC was a new isolate of AngHV-1. Thus, our results indicated that AngHV-1-FC can infect farmed American eels, with a high pathogenicity, providing new knowledge in regard to the prevalence and prevention of AngHV-1. Full article

As a functional feed additive, grape seed proanthocyanidin extract has received a lot of attention due to its biological activity in the health of aquatic animals, but its high cost limits the application of this feed additive in the diet of many fish species. It is thus urgent to develop a new resource of proanthocyanidin extract. We aimed to investigate the effects of dietary supplementation with peanut skin proanthocyanidins (PSPc) on growth parameters and lipid metabolism of juvenile American eel (Anguilla rostrata). Four hundred and fifty juvenile eels were randomly divided into five groups fed diets with five PSPc supplementation levels. The trial lasted for 8 weeks. Dietary PSPc supplementation significantly improved weight gain and feed utilization, and the best growth performance was found in the group fed with 900 mg/kg PSPc. PSPc supplementation significantly affected the crude protein level of whole fish and serum lipid parameters, and the best lipid-lowering effect was found in the fish fed with 900 mg/kg PSPc. Dietary PSPc supplementation increased lipolytic enzyme activities and decrease lipid synthase levels in the liver. The lipid metabolites affected by 900 mg/kg PSPc in the liver were mainly upregulated phosphatidylethanolamine in autophagy, downregulated ceramides in sphingolipid metabolism, upregulated phosphatidylcholine and phosphatidylethanolamine, downregulated 2-lysophosphatidylcholine in glycerophospholipid metabolism, and upregulated phosphatidylcholine in linoleic acid metabolism. In conclusion, an appropriate level of PSPc might effectively improve growth performance and regulate the lipid metabolism of the juvenile American eel, and 900 mg/kg PSPc is recommended in the diet of this fish species. Full article

The present trial was conducted to evaluate the supplementation effects of Macleaya cordata extract (MCE) on growth performance, serum biochemical parameters, and intestinal health of the juvenile American eel (Anguilla rostrata). The 480 juvenile American eels (10.93 ± 0.06 g) were randomly divided into four groups. They were fed on diets supplemented with MCE levels of 0, 25 mg/kg, 50 mg/kg, and 100 mg/kg for ten weeks, respectively. The 50 mg/kg or 100 mg/kg MCE could significantly improve growth performance, and increase the activities of acid phosphatase and alkaline phosphatase, as well as the level of high-density lipoprotein cholesterol. These levels of MCE also decreased the levels of D-lactate acid, triglyceride, and total cholesterol and the activities of aspartate aminotransferase, alanine aminotransferase, and diamine oxidase. The antioxidant ability, muscular thickness, and fold height of the intestine were enhanced by 50 mg/kg or 100 mg/kg MCE. There was no significant difference in the above parameters of groups fed with 50 mg/kg or 100 mg/kg of MCE. The beneficial effects on the intestinal microbiota were demonstrated in the group fed with 50 mg/kg MCE. In conclusion, the 50 mg/kg MCE could be used in the diet to improve the growth performance and health status of the juvenile American eels. Full article

As growth-promoting feed additives, compound acidifiers (CAs) have been widely reported in many farmed fish species, whereas there is little information on the application of CAs in the eel diet. The present trial was conducted to evaluate the supplementation effects of CAs on growth performance, serum biochemical parameters, and body composition of the juvenile American eel (Anguilla rostrata). The CAs supplementation levels in the diet of American eel were 0, 2.0, 3.0, 4.0, and 5.0 g/kg, respectively. The trial lasted for 12 weeks. The most beneficial effects of CAs on promoting growth performance, decreasing levels of serum lipid, modifying parameters of the liver function and immune function in the serum, and increasing the utilization of calcium and phosphorus in the diet were observed in the fish fed with 4.0 g/kg CAs. Dietary CAs supplementation had no significant effects on the body composition of whole fish, whereas 5.0 g/kg of dietary CAs supplementation exerted negative effects on growth performance, serum biochemical parameters, and utilization of calcium and phosphorus. The recommended level of CAs in the diet was 3.5–3.7 g/kg to achieve the optimal weight gain and feed conversion ratio for the juvenile American eel. Full article

Adult American eels (Anguilla rostrata) are vulnerable to hydropower turbine mortality during outmigration from growth habitat in inland waters to the ocean where they spawn. Imaging sonar is a reliable and proven technology for monitoring of fish passage and migration; however, there is no efficient automated method for eel detection. We designed a deep learning model for automated detection of adult American eels from sonar data. The method employs convolution neural network (CNN) to distinguish between 14 images of eels and non-eel objects. Prior to image classification with CNN, background subtraction and wavelet denoising were applied to enhance sonar images. The CNN model was first trained and tested on data obtained from a laboratory experiment, which yielded overall accuracies of >98% for image-based classification. Then, the model was trained and tested on field data that were obtained near the Iroquois Dam located on the St. Lawrence River; the accuracy achieved was commensurate with that of human experts. Full article