Largemouth Research Articles

Mummy of a juvenile sabre-toothed cat Homotherium latidens from the Upper Pleistocene of Siberia.

The frozen mummy of the large felid cub was found in the Upper Pleistocene permafrost on the Badyarikha River (Indigirka River basin) in the northeast of Yakutia, Russia. The study of the specimen appearance showed its significant differences from a modern lion cub of similar age (three weeks) in the unusual shape of the muzzle with a large mouth opening and small ears, the very massive neck region, the elongated forelimbs, and the dark coat color. Tomographic analysis of the mummy skull revealed the features characteristic of Machairodontinae and of the genus Homotherium. For the first time in the history of paleontology, the appearance of an extinct mammal that has no analogues in the modern fauna has been studied.

Analysis of the Prevalence of Bacterial Pathogens and Antimicrobial Resistance Patterns of Edwardsiella piscicida in Largemouth Bass (Micropterus salmoides) from Guangdong, China

To gain insights into the prevalence and antimicrobial resistance patterns of major bacterial pathogens affecting largemouth bass (Micropterus salmoides) in the Pearl River Delta (PRD) region, Guangdong, China, a study was conducted from August 2021 to July 2022. During this period, bacteria were isolated and identified from the internal organs of diseased largemouth bass within the PRD region. The antimicrobial resistance patterns of 11 antibiotics approved for use in aquaculture in China were analyzed in 80 strains of Edwardsiella piscicida using the microbroth dilution method. The results showed that 151 bacterial isolates were obtained from 532 samples, with E. piscicida (17.29%, 92/532), Aeromonas veronii (4.70%, 25/532), and Nocardia seriolae (2.26%, 12/532) being the main pathogens. Notably, E. piscicida accounted for the highest proportion of all isolated bacteria, reaching 60.92% (92/151), and mainly occurred from November to April, accounting for 68.48% (63/92) of the cases. The symptoms in largemouth bass infected with E. piscicida included ascites, enteritis, and hemorrhaging of tissues and organs. The drug sensitivity results showed that the resistance rates of all E. piscicida strains to ciprofloxacin, all sulfonamides, thiamphenicol, florfenicol, enrofloxacin, doxycycline, flumequine, and neomycin were 96.25%, 60–63%, 56.25%, 43.75%, 40%, 32.5%, 16.25%, and 1.25%, respectively. In addition, 76.25% (61/80) of these strains demonstrated resistance to more than two types of antibiotics. Cluster analysis revealed 23 antibiotic types (A–W) among the 80 isolates, which were clustered into two groups. Therefore, tailored antibiotic treatment based on regional antimicrobial resistance patterns is essential for effective disease management. The findings indicate that in the event of an Edwardsiella infection in largemouth bass, neomycin, doxycycline, and flumequine are viable treatment options. Alternatively, one may choose drugs that are effective as determined by clinical drug sensitivity testing.

Deciphering the transcriptional regulatory networks of FOX genes in nitrite-induced spleen injury in largemouth bass

Deciphering the transcriptional regulatory networks of FOX genes in nitrite-induced spleen injury in largemouth bass

Variation in the intestinal bacterial community composition under different water temperature culture conditions in largemouth bass (Micropterus salmoides).

This study aimed to investigate the impact of temperature on the intestinal microbiota of largemouth bass using 16S rRNA gene amplicon sequencing, focusing on the under-explored role of abiotic factors in shaping the gut microbial community. Five water temperature groups (20.0±0.2°C, 25.0±0.2°C, 28.0±0.2°C, 31.0±0.2°C, and 35.0±0.2°C) were established, each with three replicates. Significant variations in intestinal bacterial community composition were observed across these conditions. Elevated temperatures (31.0±0.2°C and 35.0±0.2°C) led to an increase in opportunistic pathogens such as OTU180 Vibrio and OTU2015 Vogesella (P<0.05). Species correlation network analysis showed a shift towards more positive relationships among intestinal microbes at higher temperatures (P<0.05). Ecological process analysis highlighted a greater role of ecological drift in microbial community structure at 31.0±0.2°C and 35.0±0.2°C (P<0.05). The study suggests that higher temperatures may predispose largemouth bass to opportunistic pathogens by altering their intestinal microbiota. Effective water temperature management is crucial for largemouth bass aquaculture to mitigate pathogen risks and maintain a balanced intestinal microbiota. This research provides critical insights into the temperature-microbiota relationship and offers practical recommendations for aquaculture practices.

Effects of dietary protein levels with cottonseed protein concentrate inclusion on growth, feed utilization, liver health and intestinal microbiota of juvenile largemouth bass (Micropterus salmoides)

An 8-weeks growth trial was conducted to evaluate the effects of dietary protein levels mainly based on cottonseed protein concentrate (CPC) meal on growth performance, protein metabolism, liver health and intestinal microbiota of largemouth bass (Micropterus salmoides) juveniles. Five isolipidic (100 g/kg) diets were prepared with protein levels ranging from 400 to 560 g/kg, with CPC of 155 g/kg, 214 g/kg, 272 g/kg, 330 g/kg, 390 g/kg to obtain five experimental diets with gradient protein levels (399.9 g/kg, 428.0 g/kg, 462.8 g/kg, 503.5 g/kg and 541.5 g/kg, respectively (CPC1, CPC2, CPC3, CPC4 and CPC5)). 300 fish (initial body weight: 14.71 ± 0.50 g) were randomly assigned into 15 tanks (3 tanks per diet). The results showed that, the fish of CPC5 group had the highest specific growth rate (SGR), weight gain (WG) and feed efficiency (FE) (P < 0.05). Increased dietary protein up-regulated most liver key genes of mTOR pathway (akt, tor, s6k, 4ebp1, s6) while down-regulated atf4 at medium dietary protein (P < 0.05). The expression of fas was down-regulated with increased dietary protein, while dgat1 was higher at CPC5 group (P < 0.05). The genes related to lipolysis were up-regulated with increased dietary protein (P < 0.05). The key genes of apoptosis including bcl2, casp9, casp3 (apoptosis) oxidative stress and endoplasmic reticulum stress were significantly up-regulated at high dietary protein (P < 0.05), which reduced the antioxidant and anti-stress capacity of the liver. Dietary 462.8 g/kg protein could maintain the normal composition and metabolic function of intestinal microbiota. In summary, dietary protein requirement using CPC as main protein source was estimated to be 463 g/kg to 510 g/kg for liver health or best growth of largemouth bass juveniles.

Antioxidant anthocyanin synergistic immune enhancer nanopeptide C-I20 remarkably enhances the protective effect of largemouth bass against largemouth bass ranavirus

Largemouth bass ranavirus (LMBV) infection results in huge economic losses in largemouth bass (Micropterus salmoides) industry. Nanopeptide C-I20 and anthocyanins have a positive effect on promoting immune responses and antioxidant mechanisms in several aquatic organisms, and are therefore used to inhibit LMBV infection. In this study, we developed an LMBV immersion challenge model using three different viral concentrations (1×104 copies/mL, 1×105 copies/mL, and 1×106 copies/mL) to infect largemouth bass, and LMBV-MCP mRNA expression was detected in infected fish. Following infection, the fish exhibited severe external ulceration, redness swelling, and darkening of the skin. Histopathological examination revealed significant necrosis and inflammation in muscle tissue, epithelial cell shedding in renal tubules, macrophage aggregation centers and cellular vacuolization in spleen and head kidney, and cellular hypertrophy in liver. To mitigate LMBV infection, we explored the protective effects of a combined treatment strategy involving C-I20 and anthocyanin. Overall, the combination of anthocyanin and C-I20 demonstrated the highest protective efficacy, significantly reducing viral loads in muscle, liver, spleen, and head kidney. Moreover, this treatment regimen enhanced antioxidant enzyme activities (T-AOC, TSOD, GSH-Px, CAT) and modulated important immune genes (IL-1, IL-8, TNF-α, IL-10, Mx, and IgM) expression. In conclusion, the synergistic application of anthocyanin and C-I20 demonstrates significant efficacy in mitigating LMBV infection. This research introduces a novel and promising approach to managing infectious diseases in aquaculture settings.

The impact of crowding stress on growth and intestinal integrity in largemouth bass (Micropterus salmoides): Insights into ER stress, autophagy and apoptosis

Crowding stress is a common abiotic stressor in intensive aquaculture that negatively impacts fish species, leading to growth depression. This study primarily explored the effects of crowding stress on the growth and intestinal integrity of largemouth bass (Micropterus salmoides). A 10-week feeding experiment was conducted with two groups: a control group (0.55 kg/m³) and a crowding stress group (1.10 kg/m³). The results showed that crowding stress significantly impaired fish growth and compromised intestinal integrity. To further elucidate the underlying mechanisms, we investigated the effects of crowding stress on endoplasmic reticulum (ER) stress, autophagy and apoptosis. Our findings revealed an increased proportion of terminal deoxynucleotidyl transferase (TdT) dUTP Nick-End Labeling (TUNEL)-positive cells and ER swelling in the intestines of stressed fish, along with a higher number of autophagosomes. Furthermore, there was a significant upregulation in the mRNA expression of genes related to ER stress, autophagy and apoptosis, including GRP78, eIF2α, IRE1, atg3, LC3-2, ulk1α, P62, and caspase-8. In conclusion, crowding stress negatively affects fish growth and intestinal integrity, potentially through the induction of apoptosis and autophagy associated with ER stress-mediated unfolded protein response (UPR). These findings provided critical insights into how intensive aquaculture disrupts intestinal integrity and inhibits growth in fish, offering a valuable reference for future research aimed at enhancing stress resistance in fish under intensive aquaculture conditions.

Kidney transcriptome analysis reveals the molecular responses to salinity adaptation in largemouth bass (Micropterus salmoides)

Kidney transcriptome analysis reveals the molecular responses to salinity adaptation in largemouth bass (Micropterus salmoides)

Integration of transcriptome, histopathology, and physiological indicators reveals regulatory mechanisms of largemouth bass (Micropterus salmoides) in response to carbonate alkalinity stress

Integration of transcriptome, histopathology, and physiological indicators reveals regulatory mechanisms of largemouth bass (Micropterus salmoides) in response to carbonate alkalinity stress

Antiviral effects of rhein on largemouth bass ranavirus (LMBRaV)

Antiviral effects of rhein on largemouth bass ranavirus (LMBRaV)

Regional Factors Affecting Smallmouth Bass and Largemouth Bass Recruitment in Midwestern USA Reservoirs

ABSTRACTRegional factors correlated with recruitment of black bass (largemouth bass; Micropterus nigricans and smallmouth bass; Micropterus dolomieu), two important fishes, are rarely studied, despite the importance of recruitment variation in influencing fish populations. We sought to identify factors that drove variation in age‐0 and age‐1 black bass abundance. Age‐0 or age‐1 black bass catch per unit effort (CPUE) in reservoirs in Kansas and Illinois, USA, was positively correlated with local short‐term (i.e., mean April precipitation) environmental variables. In contrast, age‐0 or age‐1 black bass CPUE was generally negatively correlated with long‐term environmental variables and river regulation metrics (i.e., reservoir elevation) in the Mississippi and Missouri river reservoirs. Our findings highlight that consideration of spatiotemporal scale is important when managing black bass populations.

Assessing microplastic abundances in freshwater fishes in a subtropical African reservoir

Microplastics are emerging pollutants of global concern, and their presence in the aquatic environment poses a serious risk for aquatic biota. While many studies have been conducted on the presence of microplastics in marine habitats, little research has been done in freshwater African reservoirs on microplastic pollution and their impacts on fish within the subtropical regions. To bridge this gap, the current study investigated microplastic abundances and distribution in freshwater fish within Nandoni reservoir, South Africa, across two seasons (i.e., hot–wet, cool–dry). Fish were randomly sampled using seine and gill nets from seven sites within the reservoir. In the laboratory, fish were then sorted according to taxa before dissecting them to remove the gills and the gastrointestinal tract (GIT). The organs were digested using hot hydrochloric acid and hydrogen peroxide, and the microplastics were classified according to their colours and shapes. Among the 94 fishes (i.e., 8 species) examined, microplastics were detected in 86.6% of the eight species caught. Microplastics were dominant in the gills and GIT during the cool–dry and hot–wet seasons, respectively. High microplastic abundances were found in the gills of Micropterus salmoides and the GIT of Coptodon rendalli, where fibres and the transparent colour were the most dominant. The results further showed high microplastic abundances in benthopelagic feeders highlighting that habitat influences fish consumption of microplastics whether directly or indirectly. Significant differences were observed in the feeding zone and season for all microplastic types. Microplastic sources in the reservoirs could be due to anthropogenic activities such as illegal dumping, fishing, and agriculture. Thus, there is a need for further investigation into the relation of fish weight, fish sex and body in relation to microplastic pollution. The highlighted ecological factors should be taken into consideration for future research and management actions aimed at mitigating and protecting the negative impacts of microplastic pollution on environmental and human health.

Linking fish bioturbation to life history in a eutrophic wetland: An analysis of fish contributions to internal nutrient loading

Abstract Bioturbation (sediment disturbance by animal actions) effects on nutrient cycling and nutrient levels in surface waters are difficult to quantify, in part because the diversity and magnitude of species‐specific influences are poorly understood. These influences may have consequences for the management of the trophic state of freshwater ecosystems. Fish cause bioturbation in freshwater and marine ecosystems by digging in benthic sediments, manipulating periphyton mats while searching for prey and scraping hard substrates while feeding. We used experimental enclosures (2.25 m2) to quantify bioturbation‐mediated phosphorus (P) and nitrogen (N) regeneration from sediment by three species of fish that differ in interactions with the benthos (largemouth bass, Micropterus salmoides; tilapia, Oreochromis spp.; and sailfin catfish, Pterogoplichthys spp.) in shallow eutrophic wetlands in Southern Florida. Tilapia are omnivores that include detritus in their diet (winnowing or ingesting sediments) and dig nests in soft sediments year round, sailfin catfish actively burrow into substrate and consume detritus (digging and ingesting sediments), and largemouth bass are piscivores that do not routinely interact with the benthos when feeding but may dig nests in soft sediment in spawning season (January–April). We quantified the amount of suspended flocculent organic matter and changes in water column nutrients (total phosphorus [TP] and total nitrogen [TN]) in 2‐week trials for each species and estimated the portion of nutrient increases relative to fishless controls that could be attributed to bioturbation‐mediated internal nutrient loading through suspension of organic matter (as opposed to excretion or other sources of nutrient loading). Water column nutrient concentrations increased with increasing biomass for all species, but the bioturbation contribution differed by species. Largemouth bass increased water column nutrient concentrations (TP: 86% and TN: 5% relative to controls) but did not influence water column suspended particulate matter through bioturbation of sediment. Tilapia increased water column nutrients a modest amount (TP: 8%; TN: 15%), of which a small portion was attributed to bioturbation (c. 18% of TP). Sailfin catfish raised water column nutrients substantially (TP: 105%; TN: 46%) and up to 100% of the increased TP was attributed to bioturbation. Sailfin catfish also suppressed algal growth and TP accumulation on the sides of the enclosures and reduced nutrient concentrations of the flocculent sediments. Our results were consistent with our hypothesis that behaviour and foraging traits affect bioturbation contributions to nutrient loading. The results also demonstrated that species with similar net effects like largemouth bass and sailfin catfish, added nutrients via different mechanisms (i.e. excretion vs. bioturbation). Considering the feeding strategies and interactions with the substrate of common fish species may assist managers in meeting nutrient reduction goals for eutrophic wetlands and managed freshwater systems.

Characteristics of Water Environment and Intestinal Microbial Community of Largemouth Bass (Micropterus salmoides) Cultured Under Biofloc Model

To investigate the effects of biofloc mode on the water environment and intestinal microbial community structure of largemouth bass, a 60-day culture experiment was conducted without water replacement in 300-L glass tanks. The experiment included a control group and a biofloc group, each with three replicates. The results showed the following: (i) the richness and diversity of the water environment and fish intestinal microbial community increased under the biofloc model; (ii) Proteobacteria, Patescibacteria, and Bacteroidota were the dominant phyla in the water environment of largemouth bass, while Proteobacteria, Firmicutes, Bacteroidota, Patescibacteria, and Actinobacteriota were the dominant phyla in the gut of largemouth bass. However, differences in the relative abundance and community structure of microorganisms were observed between the two groups, suggesting that the biofloc system impacts both the water environment and intestinal microbial community structure in largemouth bass culture. (iii) A correlation analysis between water quality indices and enzyme activity with microbial abundance revealed that microbial community composition could effectively reflect water quality and fish physiological health. Based on the analysis of microbial community structure, this study offers a theoretical foundation for integrating largemouth bass culture with the biofloc system, and provides valuable data for future health management and water quality control in largemouth bass production.

Hyperosmolality tolerance of freshwater largemouth bass Micropterus salmoides to brackish in early ontogenetic stages of eggs, embryos, and yolk-sac larvae

Hyperosmolality tolerance of freshwater largemouth bass Micropterus salmoides to brackish in early ontogenetic stages of eggs, embryos, and yolk-sac larvae

Characterization, expressional and evolutionary analysis of five fish-specific CCRs (CCR4La, CCR4Lc, CCR12a1, CCR12a2, and CCR12b) in largemouth bass (Micropterus salmoides)

CC chemokine receptors (CCRs), the numbers of the G protein-coupled receptor (GPCR) superfamily, had crucial roles in treating infection, inflammation, and tissue damage by binding to their ligands. In this study, five fish-specific CCRs, namely CCR4La, CCR4Lc, CCR12a1, CCR12a2, and CCR12b, were identified in largemouth bass (Micropterus salmoides). The correction of nomenclatures of these CCRs were confirmed by phylogenetic analysis, structural analysis and genomic synteny analysis. Following 1×106 CFU/mL and 1×107 CFU/mL Edwardsiella piscicida infection, these five CCRs were significantly induced in spleen of largemouth bass, indicating their important roles in the immune response against bacterial infection. Selection pressure analysis revealed that CCR4La, CCR4Lc, CCR12a1, and CCR12a2 underwent negative selection pressure, whereas CCR12b experienced positive selection pressure. Robust selection site detection methods identified that positive selected sites of CCR4La, CCR4Lc, CCR12a1, and CCR12a2 mainly distributed in their extracellular regions, which involved in ligand binding and pathogen interaction. Similarly, the positive selected sites of CCR12b were also located in its extracellular regions. The accuracy of the pressure selected sites were also validated by molecular docking analysis. The potential ligands for these five CCRs were identified by molecular docking analysis, with finding that CCL3 and CCL5 might be the ligands of largemouth bass CCR4La/Lc, and CCL5, CCL8, CCL7, CCL13 and CCL26 might be that of largemouth bass CCR12a1/a2/b. Our results provided basis for elucidating the functions of chemokine-receptor complex in largemouth bass.

RNA-seq and whole-genome re-sequencing reveal Micropterus salmoides growth-linked gene and selection signatures under carbohydrate-rich diet and varying temperature

This study was performed on Micropterus salmoides to determine growth-linked gene and single nucleotide polymorphism (SNP) markers under carbohydrate diet and varying temperature through RNA-seq and whole-genome re-sequencing. The results showed that growth-related genes were primarily enriched in the fat digestion and absorption signaling pathway, playing a role in lipid transport and metabolism. Fatty acid binding protein 6, bile salt-activated lipase-like, lysophosphatidylcholine acyltransferase 2, phospholipase A2, minor isoenzyme-like, and phospholipase A2, group IB (pancreas) were identified as the crucial genes. The differentially expressed genes between high and low temperatures were enriched in the pentose phosphate pathway, with carbohydrate transport and metabolism were most affected by temperature. Major facilitator superfamily domain containing 10, phosphogluconate dehydrogenase, fructose-1,6-bisphosphatase 1a, and spinster homolog 3 transcript variant X1(spns3) were the shared genes affected by temperature. From all the common genes, 10 growth-associated SNP markers were identified. The TT genotype at rs7781 was associated with lower body weight, while AA genotype at rs31434173 and CC genotype at rs31435313 showed positive correlation with body weight. Analogously, the GG genotype at rs31436887 and AA genotype at rs31438769 also found to characterize better growth performance. At low temperature, individuals with the AA genotype at rs11506587 and rs31435313 exhibited the slowest growth. For the genotypes labeled with rs11510589, the GG individual grew faster than the AA individual, whereas the opposite phenomenon occurred in these genotypes when labeled with rs11511314. The genotypes at rs32970704 and rs32967921 showed no growth correlation. The AA genotype at rs31435313 in spns3 had the slowest growth under a carbohydrate-rich diet regardless of the temperature. Our study presents candidate genes and SNP markers associated with growth influenced by carbohydrate and temperature, providing basis for the development of M. salmoides strain that better accepts carbohydrate diets at varying temperature.

Effects of dietary fish meal replacement by Periplaneta americana meal on growth, metabolism, intestinal health and resistance against Aeromonas hydrophila of Micropterus salmoides

An 8-week culture experiment was conducted to investigate the effects of partial replacement of fish meal (FM) with Periplaneta americana meal (PAM) on growth performance, body composition, serum biochemical parameters, intestinal health and resistance against Aeromonas hydrophila of largemouth bass, Micropterus salmoides. A total of 450 healthy largemouth bass with an initial body weight (IBW) of 14.55±0.09 g were randomly divided into five groups. Five experimental diets were prepared by replacing 0 % (P0), 15 % (P15), 30 % (P30), 45 % (P45) and 60 % (P60) of the FM in the basal diet with PAM, respectively. The results showed that final body weight (FBW), weight gain rate (WGR), and specific growth rate (SGR) were no significant difference in P15 and P30 compared with the control group (P > 0.05). Crude protein of whole fish body was significantly increased and crude lipid was significantly decreased in all PAM groups (P < 0.05). In the P30, the antioxidant enzyme activities were significantly higher than those in the control and other experimental groups, and malondialdehyde (MDA) was significantly decreased (P < 0.05). The activities of α-amylase and pepsin increased significantly in P15 and P30 and decreased significantly in P45 and P60 (P < 0.05). Lipase was significantly increased in all groups except P15 than in the control group (P < 0.05). There were no significant differences in villus height (VH), crypt depth (CD), and muscle thickness (MT) among all groups (P > 0.05), but villus width (VW) was significantly decreased in P45 and P60 (P < 0.05). The relative expression of IL-10 and TGF-β1 were first up-regulated and then down-regulated, while IL-8 was opposite (P < 0.05). The relative expression of Casp3, Casp9 and IFN-γ were significantly up-regulated in P45 and P60 (P < 0.05). After injecting A. hydrophila, all groups of largemouth bass experienced mortality, but cumulative mortality was lowest in the P30. In conclusion, PAM can partially replace FM in the diet of juvenile largemouth bass. The replacement of no more than 30 % is unlikely to adversely affect growth performance, and can increase the crude protein content of the whole fish body, and is beneficial to intestinal health.

MrFeed Pro50 FF supplementation improves growth of Largemouth Bass fed a diet containing 160‐g/kg fish meal

AbstractObjectiveThis study aimed at evaluating the role of a novel commercial product, MrFeed Pro50 FF (MP50), as a functional ingredient with which to formulate low‐fish‐meal diets for Largemouth Bass Micropterus nigricans.MethodsSeven test diets were examined. A reference diet (RD) contained 400‐g/kg fish meal, and a control diet (C) was formulated by replacing 60% of the fish meal in RD with poultry by‐product meal. The other five diets were formulated by adding MP50 to C at 5.0 (D50), 7.5 (D75), 10.0 (D100), 12.5 (D125), or 15.0 (D150) g/kg. Fish (initial body weight = 9.2 ± 0.1 g) were fed the test diets for 8 weeks.ResultThe MP50 supplementation level significantly affected weight gain, final body weight, carbon retention efficiency, energy retention efficiency (ERE), hepatosomatic index (HSI), viscerosomatic index (VSI), the ratio of fish meal consumption to fish production (RCP), and carbon waste. The weight gain of fish fed D50, D75, and D100 was greater than that of fish fed C and D150. The ERE was greater in fish fed D50 and D100 than in fish fed C and D75. The HSI and VSI were greater and nitrogen and carbon wastes were lower for fish fed D50 and D100 than in fish fed C. Fish fed D50, D75, and D100 exhibited greater weight gain and lower RCP values compared with fish fed RD. The weight gain of fish fed RD did not significantly differ from the weight gain of fish fed C, D125, and D150, confirming that the minimum fish meal level could be reduced to 160 g/kg.ConclusionThis study indicates that MP50 at 5.0–10.0 g/kg can be used as a functional ingredient in low‐fish‐meal diets for Largemouth Bass.

Comparison and evaluation of DNA vaccines against Nocardia seriolae infection in largemouth bass (Micropterus salmoides)

Chronic granulomatous diseases caused by Nocardia seriolae have resulted in substantial economic losses for the aquaculture industry. DNA vaccines are considered a promising approach for controlling infectious diseases. To develop effective DNA vaccines against N. seriolae, we selected Ag85L, MmaA4, HspX, Rv3407, and HtpG as candidate antigens. Among these, pcDNA-Ag85L and pcDNA-MmaA4 were the most effective against N. seriolae infection in largemouth bass (Micropterus salmoides), achieving the highest relative percentage survival (RPS) rates of 78.6 % and 92.9 %, respectively. Tissue bacterial loads and histopathological tests revealed a significant reduction in bacterial abundance in the liver, spleen, head kidney, and trunk kidney of the immunised groups compared to that in the control group. Additionally, no distinct pathological changes were observed in the spleen or head kidney tissues. The expression levels of immune-related genes including IL-1β, IL-8, MHCI, MHCII, CD4, and CD8α were significantly upregulated in the pcDNA-Ag85L and pcDNA-MmaA4 immunised groups, thus indicating that the two DNA vaccines mediated immune protection by promoting both humoral and cellular immune responses. Overall, the pcDNA-Ag85L and pcDNA-MmaA4 DNA vaccines demonstrated strong potential for protecting largemouth bass against N. seriolae infection, offering an innovative solution for controlling granulomatous diseases in fish.