Search Results (142)

Veterinary drug residues in aquatic products are often overlooked, yet they pose significant environmental risks and potential threats to human health. In this study, a rapid and sensitive analytical method was developed for the simultaneous determination of nine commonly used macrolide antibiotics in largemouth bass (Micropterus salmoides) muscle using ultrahigh-performance liquid chromatography–tandem mass spectrometry (UHPLC-MS/MS). Sample extraction was performed using 80% acetonitrile in water, followed by purification with Cleanert MAS-Q cartridges. Chromatographic separation was achieved on a Waters ACQUITY UPLC BEH C₁₈ column (50 mm × 2.1 mm; 1.7 μm), equipped with a Waters VanGuard^TM BEH C₁₈ guard column (1.7 μm), using a mobile phase consisting of 0.1% formic acid in water and 0.1% formic acid in acetonitrile. Mass spectrometric detection was conducted in positive electrospray ionization mode (ESI⁺) using multiple reaction monitoring (MRM). The method demonstrated excellent linearity in the concentration range of 0.2–30 ng/mL, with determination coefficients (R²) exceeding 0.9980 for all analytes. Average recoveries ranged from 89.3% to 108.4%, with intraday and interday relative standard deviations (RSDs) of 2.9–11.6% and 4.1–12.5%, respectively. The limits of detection (LOD) and quantification (LOQ) for largemouth bass muscle were determined to be 0.4 μg/kg and 2.0 μg/kg, respectively. The decision limits (CC_α) and detection capabilities (CC_β) ranged from 2.13 to 215.71 μg/kg and 2.22 to 231.42 μg/kg, respectively. The developed method was successfully applied to the quantitative analysis of macrolide residues in 20 largemouth bass samples collected from local markets. Full article

We performed a diagnostic disease investigation on a wild smallmouth bass (Micropterus dolomieu) with skin ulcers that was collected from Lake Oahe, South Dakota, following reports from anglers of multiple fish with similar lesions. Gross and histologic lesions of ulcerative dermatitis, myositis, and lymphocytolysis within the spleen and kidneys were consistent with largemouth bass virus (LMBV) infection. LMBV was detected by conventional PCR in samples of a skin ulcer, and the complete genome sequence of the LMBV (99,184 bp) was determined from a virus isolate obtained from a homogenized skin sample. A maximum likelihood (ML) phylogenetic analysis based on the major capsid protein (MCP) gene alignment supported the LMBV isolate (LMBV-SD-2023) as a member of the species Ranavirus micropterus1, branching within the subclade of LMBV isolates recovered from North American largemouth (Micropterus salmoides) and smallmouth bass. This is the first detection of LMBV in wild smallmouth bass from South Dakota. The ultrastructure of the LMBV isolate exhibited the expected icosahedral shape of virions budding from cellular membranes. Viral nucleic acid in infected cells was visualized via in situ hybridization (ISH) within dermal granulomas, localized predominantly at the margin of epithelioid macrophages and central necrosis. Further sampling is needed to determine the geographic distribution, affected populations, and evolutionary relationship between isolates of LMBV. Full article

This study was performed to investigate the effects of dietary yeast culture (YC) supplementation on growth performance, digestive function, intestinal inflammatory response, and microbiota composition of largemouth bass Micropterus salmoides (LMB). Six diets were formulated with graded levels of YC (0, 5, 10, 15, 20, and 30 g/kg), referred to as CON, YC5, YC10, YC15, YC20, and YC30, respectively. Each diet was assigned to four replicate tanks of LMB juveniles (initial body weight 8.11 ± 0.05 g) with twenty fish per tank. After an 8-week feeding trial, final body weight and specific growth rate showed an increasing trend with 5~20 g/kg YC and reached a maximum at 15 g/kg YC. Feeding ratio decreased, but feed efficiency ratio (FER) improved in response to dietary YC inclusion, and FER was higher in the YC10 fish than in the YC5, YC20, and YC30 fish. Proximate composition (moisture, protein, and lipid) of the whole fish was not affected by dietary YC levels. The activities of intestinal lipase and trypsin were higher in the YC10 fish, while the relative expression of interleukin-8 (il-8) and il-1β was downregulated in the hindgut of the YC15 fish compared with the CON fish. Histological examination showed that the villus height of the midgut, together with goblet cell density of the foregut and midgut, was higher in the YC10 and YC30 fish than in the CON fish. 16S rRNA sequencing showed that Proteobacteria, Fusobacteria, and Firmicutes dominated the intestinal microbiota in LMB. The decrease in harmful Mycoplasma accounted for the dramatic change in Firmicutes abundance, while the increase in Cetobacterium (specifically C. somerae) accounted for the change in Fusobacteria abundance in the gut of the YC10 and YC30 fish compared with the CON fish. The increase in the beneficial Endozoicomonas was the main reason for the change in Proteobacteria abundance in the intestine of the YC30 fish as compared with the CON fish. Taken together, the alteration of intestinal microbiota composition contributed to the improved digestive function and feed utilization in LMB fed YC-supplemented diets. Based on growth performance, the optimal YC level in the diet for LMB was 15 g/kg. Full article

To address the negative effects of high-starch diets on largemouth bass (LMB), this study evaluated the feasibility of using a Gracilaria lemaneiformis-konjac glucomannan mixture (GKM, 2:1) as a substitute for strong flour (SF). Four iso-nitrogenous and iso-lipid diets were formulated: a control (15% SF; GK00) and three other diets replacing 33.3% (GK05), 66.7% (GK10), or 100% (GK15) of SF with GKM. Each diet was randomly administered to triplicate tanks of fish (10.49 ± 0.232 g) for a 10-week feeding trial. Results showed that the GKM inclusion groups significantly improved the fish survival and feed intake. Fish in GK05 and GK10 groups exhibited significantly higher final body weight, weight gain, and specific growth rate than the GK00 group, while GK15 showed no significant increase in these metrics. There was no impairment in protein, lipid, phosphorus, and energy retention efficiency in the GK05 and GK10 groups compared to those of the GK00 group. Apparent digestibility for feed dry matter, protein, lipid, phosphorus, and the 16 amino acids was not decreased in the GK05 and GK10 groups relative to the GK00 group. In addition, this study revealed reduced phosphorus waste per kilogram of weight gain in GK05 and GK10. In conclusion, these findings position GKM as a sustainable alternative to SF in feed for LMB. Full article

This study aimed to evaluate the effects of dietary supplementation with sodium butyrate (SB) in different forms on the growth performance, antioxidant capacity, immune response, and intestinal health of largemouth bass (Micropterus salmoides). Five diets were formulated: a basal diet (SB0), diets with 1000 (ESB1), 1500 (ESB2), and 2000 mg/kg encapsulated SB (ESB3), and a diet with 2000 mg/kg raw powder sodium butyrate (RSB, non-encapsulated). After 49 days of feeding trials, the ESB2 group exhibited significantly higher weight gain and specific growth rates and a lower feed coefficient than those of the SB0 group (p < 0.05). Compared with the SB0 group, proximal intestinal villus length and width were significantly increased in the ESB1, ESB2, and ESB3 groups (p < 0.05). The expressions of tight junction genes zo-1, claudin-1, and claudin-4 were up-regulated in these SB-supplemented groups and most pronounced in the ESB2 group (p < 0.05). Compared with the SB0 group, antioxidant enzyme activities (catalase and superoxide dismutase) and their gene expressions increased in the ESB1, ESB2, and RSB groups (p < 0.05). Immune-related genes il-10 and tgf-β1 were up-regulated in the ESB1 and ESB2 groups, while their il-8, il-1β, and tnf-α were down-regulated (p < 0.05). The ESB2 group had higher intestinal abundance of Firmicutes and Lactobacillus. In conclusion, dietary supplementation with 1500 mg/kg encapsulated SB (ESB2) improved growth, antioxidant capacity, immunity, and gut health in largemouth bass. Full article

Crowding stress is an inevitable stressor in intensive farming, yet its underlying mechanisms are still obscure, severely hindering the aquaculture industry’s healthy development. As the primary sensory and regulatory organ for stressors, the brain plays a crucial role in stress responses. In this study, the effect of crowding stress on the telencephalon (Tel) and hypothalamus (Hy) has been explored using RNA sequencing. After four weeks of crowding stress, neuroinflammation-related genes were significantly induced in both the Tel and Hy. Additionally, cell fate-related processes were markedly altered. Neurogenesis-related pathways, including the Wnt and Hedgehog signaling pathways, were significantly enriched in both regions. The apoptosis-related genes (caspase3, p53) were predominantly downregulated in the Tel (log₂Fold Change: −1.27 and −0.71, respectively), while ferroptosis-related genes (ho1, ncoa4) were specifically activated in the Hy (log₂Fold Change: 1.15 and 0.73, respectively). The synaptic plasticity-related genes (prkcg, cacna1d) were significantly downregulated in both the Tel (log₂Fold Change: −1.78 and −0.88) and Hy (log₂Fold Change: −1.99 and −1.52). Furthermore, neurotransmitter synthesis (γ-aminobutyric acid (GABA) and serotonin (5-HT)) was disrupted in the Tel, whereas growth-related hormone gene expression was markedly altered in the Hy. These findings provide novel insights into the neurobiological mechanisms of chronic crowding stress in fish, laying a foundation for developing brain-targeted strategies to enhance welfare and mitigate stress in intensive largemouth bass farming. Full article

This study examines the impact of the arginine/lysine ratio in feed on the growth, serum amino acids, arginine metabolism, and antioxidant capacity of juvenile largemouth bass (5.95 ± 0.02 g). Five isonitrogenous and isolipidic diets with varying arginine/lysine ratios were formulated and administered over an eight-week period. The results indicated that the treatments had no significant effect on protein efficiency ratio (PER), daily feed intake (DFI), or morphological indices of juvenile largemouth bass (p > 0.05). When the arginine/lysine ratio was 0.85 (2.25/2.65; 2.54/3.00), liver antioxidant capacity was maximized, and inflammatory factors were suppressed. Conversely, a ratio of 2.25/2.99 significantly reduced weight gain (WG) and specific growth rate (SGR) in juvenile largemouth bass, inhibited arginase activity, and increased serum total nitric oxide synthase (T-NOS) activity. When lysine was in excess (2.25/2.99 group), elevating arginine content (2.54/3.00 group) enhanced growth, antioxidant, and immune performance. Analysis of glutathione metabolism and innate immune-related pathway revealed that an optimal arginine/lysine ratio mitigates inflammatory damage induced by oxidative stress. An arginine/lysine imbalance significantly elevated liver malondialdehyde (MDA) content while reducing total antioxidant capacity (T-AOC), superoxide dismutase (SOD), catalase (CAT) activities, and glutathione (GSH) content, thereby increasing the expression levels of inflammatory factors (IL1B, IL8, TGFB1, BAX). These findings demonstrate that an imbalance in arginine/lysine adversely affects the growth, metabolism, and antioxidant capacity of largemouth bass. When lysine is in excess, increasing the arginine content to achieve an arginine/lysine ratio of 0.85 alleviates the negative effects of antagonism, suggesting arginine supplementation may regulate oxidative damage caused by lysine excess. Full article

Crossbreeding often results in heterosis. In this study, we generated hybrids from largemouth bass from geographically isolated populations. Growth, digestive enzyme activity, and muscle nutrient composition were compared between the hybrid groups (NC and CN) and the purebred groups (NN and CC), and the gut microbiota was investigated. The heterosis rates of body length, body height, and body thickness in hybrid largemouth bass were statistically significant. Digestive enzyme activity was higher in the hybrid groups than in the purebred groups. Compared with the CN and CC groups, the NC group had significantly higher levels of essential amino acids and total amino acids in the muscle. The polyunsaturated fatty acid content was lower in the hybrid groups than in the purebred groups. The gut microbiota in the hybrid groups predominantly exhibited a non-additive inheritance pattern, characterized by a reduced abundance of Proteobacteria and an increased abundance of Fusobacteria. Microbial taxa showing differences in abundance between the hybrid and purebred groups harbored genes enriched in multiple amino acid and fatty acid metabolism pathways. Cetobacterium, Pseudomonas, and Stenotrophomonas were more abundant in the hybrids, and were positively correlated with multiple amino acids and fatty acids. These results highlight the critical role of gut microbiota in heterosis. Full article

In the study, a comprehensive investigation on potential bacterial pathogens affecting largemouth bass (Micropterus salmoides) was performed. Monthly surveys were conducted from April to October 2024. Diseased largemouth bass exhibited diverse clinical symptoms, such as rot of gill and fin, ulcers on body surface, and petechial hemorrhages in liver. Following isolation and identification, a total of 21 potential bacterial pathogens (numbered strain 1 to 21, respectively) were identified. The genus Aeromonas had the highest proportion (67.14%), among which the frequency of Aeromonas veronii was 24.60%. TEM analysis revealed that the bacterial strains exhibited three predominant shapes (rod-shaped, spherical, and curved) with length ranging from 0.5 to 3 μm. Flagellar structures were observed in strains 1–4, 6–8, 11–17, and 19–21, with variations in number and growth sites. Three isolates (strains 9, 10, 18) demonstrated Gram-positive characteristic, and strains 5, 11, and 18 have capsule structures. Strains 5, 9, 10, and 18 were non-motile, and strains 1–4, 6, 7, 9–11, 16–18, and 21 exhibited β-hemolysis. Physiological and biochemical characteristics of the 21 bacterial isolates were comprehensively analyzed. Antibiotic sensitivity testing revealed that florfenicol and enrofloxacin exhibited excellent antibacterial effects. These data will enrich the potential bacterial diseases information and promote the healthy development of the largemouth bass industry. Full article

The health benefits associated with microbial species inhabiting aquatic animals have garnered increasing attention, as it is expected that the colonization and efficacy of native probiotic bacteria adapted to the internal environment of the target species will be more active than non-native bacteria. In this study, six isolates were obtained from the intestinal tract of largemouth bass. Three of these isolates demonstrated higher growth ability compared to the others and were further characterized using in vitro assays. Lactococcus lactis LBM15 was found to exhibit antibacterial activity against common pathogens affecting largemouth bass; the adhesion inhibition capabilities of the isolates were systematically evaluated through competitive, repulsive, and substitutive adhesion assays. The strain inhibited adhesion to all six tested pathogen strains, with competitive adhesion inhibition rates ranging from 42% to 54%, the highest of which was observed against V. anguillarum. Repulsive adhesion inhibition rates ranged from 27% to 55%, with the highest rate noted for Edwardsiella tarda. Additionally, substitutive adhesion inhibition rates were found to range from 48% to 76%, with the highest inhibition observed against Aeromonas hydrophila. Furthermore, LBM15 exhibited favorable antimicrobial susceptibility profiles, showing sensitivity to 21 antibiotics tested. Notably, safety assessment trials were performed exposing fish to LBM15 at a concentration of 1 × 10⁹ CFU/mL by injection and at a concentration of 1 × 10⁸ CFU/mL by feed administration. No clinical abnormalities, behavioral alterations, or mortality were documented in either exposure group, confirming the safety of LBM15 for application in aquaculture. The results suggested that LBM15 isolates from largemouth bass have potential for further investigation and possible application as probiotic candidates. Full article

Background/Objectives: Largemouth bass rhabdovirus (Micropterus salmoides rhabdovirus, MSRV) disease causes high mortality in largemouth bass farming. Therefore, vaccine development is critical for largemouth bass prevention against MSRV. Methods: An attenuated strain, denoted as MSRV-0509, was selected through intraperitoneal injection and immersion challenge assays, followed by plaque purification. The biological characteristics of MSRV-0509, including optimal inoculation dose, replication kinetics, thermostability, pH resistance, chloroform tolerance, and storage viability, were determined via viral titration. Spatiotemporal distribution patterns in largemouth bass post-intraperitoneal injection or immersion infection were quantified by qPCR. Immunoprotective efficacy was evaluated through intraperitoneal and immersion vaccination. Mechanistic insights were explored via relative qPCR and serum neutralization assays. Safety was assessed by single-dose overdose immunization and virulence reversion experiments. Results: An attenuated strain MSRV-0509 was screened through a challenge assay, exhibiting complete avirulence in largemouth bass compared to the virulent strain SCRV-T6. MSRV-0509 demonstrated optimal replication at low MOI (0.0001) in CPB cells, with peak titers (10^8.3 TCID₅₀/mL) at 96 h post-infection. The virus showed susceptibility to high temperatures, lipid solvents and acidic conditions, with prolonged stable storage viability at −80 °C. Tissue distribution revealed the spleen as the primary target after intraperitoneal injection, while immersion restricted infection to gills, with rapid clearance by 3–6 dpi. Vaccination trials identified 5 × 10² TCID₅₀/fish via intraperitoneal injection and 10^6.0 TCID₅₀/mL via immersion as effective immunizing doses, providing 100% relative survival post-challenge. Immune gene expression and serum neutralization showed Th1 and Th2 activation via intraperitoneal injection (elevated IL-12, IFN-γ, IL-10, IgM), whereas only the Th1 response was activated after vaccine immersion. No abnormality and mortality were observed in single overdose vaccination and virulence reversion experiments, confirming that MSRV-0509 was safe. Conclusions: These results proved that MSRV-0509 could be a promising vaccine candidate to protect largemouth bass from MSRV disease. Full article

This study aimed to evaluate the impact of Eucommia ulmoides extract (EE) supplementation on the expression of genes related to glucose metabolism and antioxidant capacity of M. salmoides in response to different starch levels. In order to evaluate the effect of EE on fish metabolism and especially to enhance the metabolism of M. salmoides towards glucose metabolism, especially in high and low starch formulations, we designed six experimental feed groups: PC (high-starch control), NC (low-starch control), and four groups supplemented with EE on the basis of PC, with EE concentrations of 0.05%, 0.10%, 0.15%, and 0.20%, respectively. Each feed was administered to fish with an average weight of 36.98 ± 0.08 g, which were cultured for seven weeks, and the water temperature was 31–33 °C. The results demonstrated that increasing the EE concentration in the feed significantly influenced fish growth without affecting the body composition. Regarding the antioxidant activity, the highest CAT (catalase) enzyme activity in the intestine was recorded in the 0.15% EE group. Additionally, the mRNA expression of the antioxidant gene keap1 (kelch-like ECH-associated protein1) increased with higher EE supplementation, and sod (superoxide dismutase) mRNA expression was significantly elevated in the 0.10% EE group compared to that in the PC group. A plasma biochemical analysis revealed a significant increase in the ALP (alkaline phosphatase) activity in the 0.05% EE group relative to the PC group, while the TG (triglycerides) levels progressively decreased as the EE levels increased. Furthermore, the GLU (glucose) levels were significantly reduced in both the EE-supplemented and NC groups compared to those in the PC group. Among the genes associated with glucose metabolism, both gk (glucokinase) and pepck (phosphoenol pyruvate carboxykinase) exhibited a pattern of initially decreasing, followed by an increase, as the EE levels rose, with the pepck (phosphoenol pyruvate carboxykinase) expression being lowest in the 0.10% EE group. In conclusion, appropriate EE supplementation in the diet may promote growth performance, enhance antioxidant capacity, and support the expression of genes related to glucose metabolism of M.salmoides in response to different starch levels. Full article

The liver of fish is an essential metabolic organ that also serves an immune regulatory role. In this study, we constructed a model of largemouth bass (Micropterus salmoides) infected with Nocardia seriolae by injection to explore the immune and antioxidant functions of the liver. The results showed that N. seriolae infection caused severe pathological changes in the liver, including cell necrosis, granuloma formation, and leukocyte infiltration. The level of mRNA expression of immune-related genes in the liver was significantly increased 2 days post-infection. Moreover, the combined analysis of transcriptome and metabolome showed that N. seriolae infection markedly affected liver metabolism, including glutathione metabolism, arginine and proline metabolism, arachidonic acid metabolism, as well as starch and sucrose metabolism. Additionally, multiple key biomarkers were identified as involved in regulating responses to N. seriolae infection, including arginine, glutathione, gpx, GST, PLA2G, GAA, and PYG. To further elucidate the regulatory effects of arginine on the immune and antioxidant processes in the liver, primary hepatocytes were isolated and cultured. The results demonstrated that arginine supplementation significantly reduced the expression of LPS-induced apoptosis-related genes (bax, cas3, cas8, and cas9) by up to 50% while increasing the expression of antioxidant genes (gpx, GST) by up to 700% at 24 h. Through the analysis of metabolic changes and immune responses in the liver following N. seriolae infection, combined with in-vitro experiments, this study elucidated the anti-apoptotic and antioxidant effects of arginine, revealing the immune response mechanisms in fish liver and laying the groundwork for using nutritional strategies to improve fish health. Full article

The fermentation product FP-WeiGuangSu is regarded as a novel, green and efficient antibiotic substitute. Such products constitute one of the principal strategies for addressing bacterial diseases in aquaculture in the future. This study investigates the effects of FPs derived from Bacillus subtilis on the antioxidant capacity and gut microbiota of Largemouth Bass (Micropterus salmoides). Experimental diets containing 0, 1%, 3% and 5% FPs (Control, H1, H2 and H3) were fed to M. salmoides. Although short-term administration of FPs exerted no significant influence on the growth performance of Largemouth Bass, serological findings demonstrated that supplementation with FPs decreased the contents of the liver injury markers ALT, AST and AKP, along with liver MDA content, and enhanced antioxidant capacity (SOD, CAT and GSH-px). Notably, the addition of 1% FPs significantly improved the systemic antioxidant performance (SOD, CAT, GSH-px and T-AOC). Moreover, the FP supplementation increased the expression levels of il-10 and IgM, and lipolysis-related genes. The results of gut microbiota analysis revealed that FPs significantly altered the diversity and structure of gut microbiota. The LEfSe results indicated that the microbial marker of the control group was Cetobacterium, those of the H1 group were Bacillus and Mycoplasma, those of the H2 group were Acinetobacter, Paenibacillus and g_unclassified_Rhizobiaceae, and that of the H3 group was Enterococcus. The most significant microbial marker upon the addition of FPs was Paenibacillus, and the pathways for biosynthesis of secondary metabolites, biosynthesis of antibiotics, and biosynthesis of amino acids were significantly activated. The Bugbase analysis results suggested that, compared with the control group, the abundance of anaerobic bacteria in the FP group decreased, while the abundance of microorganisms with mobile-element-containing and oxidative-stress-tolerant phenotypes increased. Hence, this study demonstrated that 1–3% FP dietary supplementation can be used to enhance antioxidant ability, and liver and intestine health of M. salmoides in the aquaculture industry and can be regarded as a promising feed additive in aquaculture. Full article

The aim of this study was to investigate the effects of sodium butyrate (SB) on growth performance, digestive ability, blood health, and ammonia tolerance of largemouth bass. During the experiment, largemouth bass were fed different diets (0.00%, 0.50% and 1.00% SB) followed by a 96-h ammonia challenge. In this study, dietary supplementation of SB can improve the growth (weight gain rate increased; GH and IGF 1 genes up-regulated) of largemouth bass. The addition of SB also significantly increased serum total protein, albumin and globulin contents and reduced triglycerides, cholesterol and aspartate transaminase contents. The digestive ability (pepsin, lipase, amylase, alkaline phosphatase, creatine kinase, gamma-glutamyltranspeptidase, sodium-potassium adenosine triphosphatase, villus height and muscular thickness increased) was significantly higher in the 0.50% and 1.00% SB groups. SB also improved the anti-inflammatory capacity (IL 1 and IL 8 genes down-regulated) of largemouth bass. The addition of SB to feed significantly reduced the cumulative mortality rate after 96 h of ammonia stress. SB significantly increased liver ammonia metabolism enzyme (arginase, argininosuccinate synthetase, ornithine transcarboxylase and argininosuccinate lyase) and inducible nitric oxide synthase activity, and significantly decreased the neuronal nitric oxide synthase activity. The results indicate that dietary supplementation of SB can promote growth and improve digestive ability, blood health, and ammonia tolerance in largemouth bass. Full article