Largemouth Research Articles

Effects of Atractylodes macrocephala polysaccharide on growth performance, serum biochemical indexes, and intestinal microflora of largemouth bass (Micropterus salmoides)

IntroductionAs the aquaculture industry intensifies to enhance production efficiency and capacity, the risk of disease outbreaks in high-density systems, such as those for largemouth bass, has escalated. This necessitates the exploration of novel strategies for disease prevention and control. Studies have shown that Atractylodes macrocephala polysaccharide (AMP) possesses the functions of promoting growth and enhancing immune capacity, making it a potential feed additive in animal production.MethodsThis study aimed to assess the impact of AMP on the growth performance, serum biochemical indices, and intestinal flora structure of largemouth bass. A total of 360 healthy largemouth bass (mean weight: 15.25 ± 1.29 g) were randomly assigned to four groups, each with three replicates. The groups were fed diets supplemented with 0% (Group D, control group), 0.4% (Group A), 0.8% (Group B), or 1.2% (Group C) AMP for 42 days.ResultsThe results showed that the addition of an appropriate amount of AMP in the feed significantly improved the weight gain rate (WGR) and specific growth rate (SGR) of largemouth bass, reduced the feed conversion ratio (FCR), and enhanced growth performance. AMP reduced the levels of AST and ALT, indicating a hepatoprotective effect on largemouth bass, with significant differences from the control group (P < 0.05). AMP also improved the intestinal microbiota composition of largemouth bass, positively affecting intestinal health. The analysis of intestinal microbiota revealed 1,288 amplicon sequence variants (ASVs) in the intestine of largemouth bass in Group B, dominated by Firmicutes and Bacteroidota. In contrast, Group C (1.2%) had 920 ASVs, with Fusobacteriota and Firmicutes as the major components, while the relative abundance of Firmicutes was lower, showing significant differences from the control Group D. The functional analysis of intestinal microbiota based on KEGG showed significant differences (P < 0.05) among the four groups in Carbon metabolism, Biosynthesis of amino acids, and Metabolic pathways.DiscussionThe study concludes that the inclusion of AMP at 0.8% – 1.2% in the feed can enhance the growth performance and intestinal health of largemouth bass, offering a promising strategy for disease prevention and control in intensive aquaculture settings.

Evaluation of glycyrrhetinic acid in attenuating adverse effects of a high-fat diet in largemouth bass (Micropterus salmoides)

Glycyrrhetinic acid (GA) has been shown to promote growth characteristics and play a crucial role in anti-inflammatory responses in animals. To investigate the effects of dietary GA supplementation on growth performance, intestinal inflammation, and intestinal barrier protection in largemouth bass (Micropterus salmoides) fed a high-fat diet (HFD), a 77-day feeding experiment was conducted. A total of 750 largemouth bass, initially averaging 17.39 ± 0.09 g in body weight, were randomly allocated to five experimental groups and fed a control diet, a HFD, and the HFD diet supplemented with GA at either 0.5, 1.0, or 1.5 mg/kg, named as control, HDF, HFD+GA 0.5, HFD+GA 1.0, and 1.5 HFD+GA 1.5, respectively. Each group contained three replicates. The study revealed that dietary GA improved final body weight (P < 0.001), percent weight gain (P = 0.041), and feed intake (P < 0.001), all of which had been affected by a HFD in largemouth bass (P < 0.05). Supplementation of HFD with 1.0 mg/kg GA increased the mRNA expressions and protein levels of corresponding tight junctions, occludin, zonula occluden-1 (ZO-1) and claudin-1 in the intestines of largemouth bass. Furthermore, the addition of HFD with both of 0.5 and 1.0 mg/kg GA decreased the mRNA expressions of pro-inflammatory genes such as interleukin-1β (IL-1β), IL-18, and cysteinyl aspartate specific proteinase 1 (caspase-1), as well as proteins associated with pyroptosis-induced inflammation, including NOD-like receptor family and pyrin domain contain 3 (NLRP3), apoptosis-associated speck-like protein containing a C-terminal caspase recruitment domain (ASC), gasdermin E (GSDME), and N-terminal domain of GSDME (GSDME-N) (P < 0.05). Finally, dietary GA supplementation alleviated mitochondrial damage and reduced reactive oxygen species (ROS) production induced by the HFD. It is concluded that GA supplementation in HFD enhances growth performance, increases mRNA expression and protein levels of tight junction-related parameters, decreases mRNA expression and protein levels of pyroptosis-related genes, and alleviates intestinal mitochondrial injury and inflammation induced by HFD.

Dietary Supplementation with Nano-Curcumin Improves the Meat Quality and Nutrition Value of Largemouth Bass (Micropterus salmoides) Fed with a High-Carbohydrate Diet

This study investigated the effects of curcumin nanoparticles on the flesh quality of largemouth bass on a high-carbohydrate diet. A total of 180 fish (11.01 ± 0.02 g) were fed three semi-purified diets: the Control group (LC) were supplemented with standard carbohydrate (10%), the experimental group (HC) were supplemented with 15% carbohydrate, and the experimental group were supplemented with 0.2% nano-curcumin added to 15% carbohydrate (HCN) for 6 weeks. Results showed that a* value, taurine, valine, isoleucine, histidine, cystine, fatty acids (C17:0 and C20:2n6), MDA (malondialdehyde) content, and SOD (Superoxide dismutase) activity were significantly elevated (p &lt; 0.05) in HC. Muscle fibers showed significant increases in horizontal diameter, longitudinal diameter, and cross-sectional area (p &lt; 0.05), as well as up-regulated expression levels of the MRFS (myogenic regulatory factor) family gene and MSTN (myostatin) (p &lt; 0.05), and a significant decrease in C16:1n7 in HC (p &lt; 0.05). Importantly, the HCN group enhanced the muscle quality of largemouth bass by elevating the L* value, valine, isoleucine, arginine and cystine, C20:2n6, decreasing (p &lt; 0.05) refrigeration loss, chewability, firmness and hardness, then MDA content and SOD activity, and downregulating (p &lt; 0.05) MSTN and MRFS family gene expression levels to improve largemouth bass muscle quality.

A naturaly attenuated largemouth bass ranavirus strain provided protection for Micropterus salmoides by immersion immunization

Largemouth bass ranavirus (LMBV) causes disease outbreaks and high mortality at all stages of largemouth bass farming. Therefore, live vaccine development is critical for largemouth bass prevention against LMBV by immersion immunization. Herein, an attenuated LMBV strain with good immunogenicity, designated as LMBV-2007136, was screened from the natural LMBV strains bank through challenge assay and immersion immunization experiment. After determing the safe concentration range of LMBV-2007136, the minimum immunizing dose of immersion immunization was verified. When largemouth bass were vaccinated by immersion at the lowest concentration of 102.0 TCID50/mL, all of fish were survival post virulent LMBV challenge, and the relative percent survival (RPS) was 100 %. And the immune gene expression levels of IL-10, IL-12, IFN-γ, and IgM in the spleen and kidney post-vaccination were significantly up-regulated compared to the control group, but TNF-α expression showed no significant changes. The safety and efficacy of LMBV-2007136 at passages P8, P13, and P18 were futher assessed, and no death of largemouth bass was observed within 21 days post-immunization and RPS of three vaccination groups was 100 %, suggesting that the safety and efficacy of the attenuated strain at different passages was stable. Furthermore, in the virulence reversion test, the attenuated strain was propagated through 5 times in largemouth bass by intraperitoneal injection and no abnormality and mortality were observed, further proving the attenuated vaccine candidate LMBV-2007136 was safe. These results proved that LMBV-2007136 could be a promising candidate for a live vaccine to protect largemouth bass from LMBV disease.

A mixed animal and plant protein source replacing fishmeal affects bile acid metabolism and apoptosis in largemouth bass (Micropterus salmoides).

Chicken meal, shrimp meal, blood meal, and soybean protein concentrate (SPC) are common alternatives to fishmeal. This study used them to prepare three diets with different levels of fishmeal (FM48, FM40, FM32) for largemouth bass (Micropterus salmoides). The results found no significant difference in the growth performance of largemouth bass fed different diets. Mixed protein increased the total cholesterol (T-CHO) content in plasma, and reduced the total superoxide dismutase (T-SOD) activity in plasma and liver. Targeted metabolomics analysis found that the low fishmeal diets affected the cholesterol and bile acid metabolism of largemouth bass. Mixed protein inhibited cyp7a1 and enhanced hmgcr and pparγ mRNA levels, as well as enhanced the expression levels of FXR in the liver. The fish fed FM32 diet showed inhibited fxr, rxrα and cyp7a1 mRNA levels in the intestine. The results of TUNEL fluorescence staining showed that mixed protein induced apoptosis in largemouth bass. The caspase 3 and caspase 9 mRNA levels in the fish fed FM40 and FM32 diet significantly increased, as well as the expression levels of CASPASE 3. The experiment also found that it could induce oxidative stress and endoplasmic reticulum stress. In conclusion, replacement of fishmeal with mixed animal and plant protein diets did not affect the growth performance, but the health and bile acid metabolism of largemouth bass was affected when the fishmeal level was reduced to 32 %.

Lactobacillus casei displaying MCP2α and FlaC delivered by PLA microspheres effectively enhances the immune protection of largemouth bass (Micropterus salmoides) against LMBV infection

Largemouth bass ranavirus (LMBV) seriously affects the development of largemouth bass (Micropterus salmoides) industry and causes huge economic losses. Oral vaccine can be a promising method for viral disease precaution. In this study, MCP2α was identified as a valuable epitope region superior to MCP and MCP2 of LMBV by neutralizing antibody experiments. Then, recombinant Lactobacillus casei expressing the fusion protein MCP2αC (MCP2α as antigen, C represents flagellin C from Aeromonas hydrophila as adjuvant) on surface was constructed and verified. Further, PLA microsphere vaccine loading recombinant MCP2αC L. casei was prepared. The PLA microspheres vaccine were observed by scanning electron microscopy and showed a smooth, regular spherical surface with a particle size distribution between 100 and 200 μm. Furthermore, we evaluated the tolerance of PLA-MCP2αC vaccine in simulated gastric fluid and simulated intestinal fluid, and the results showed that PLA-MCP2αC can effectively resist the gastrointestinal environment. Moreover, the protective effect of PLA-MCP2αC against LMBV was evaluated after oral immunization and LMBV challenge. The results showed that PLA-MCP2αC effectively up-regulated the activity of serum biochemical enzymes (T-SOD, T-AOC, LZM, complement C3) and induced the mRNA expression of representative immune genes (IL-1β, TNF-α, IFN-γ, MHC-IIα, Mx, IgM) in spleen and head kidney tissues. The survival rate of largemouth bass vaccinated with PLA-MCP2αC increased from 24 % to 68 %. Meanwhile, PLA-MCP2αC inhibited the LMBV burden in spleen, head kidney and liver tissues and attenuated tissue damage in spleen. These results suggested that PLA-MCP2αC can be used as a candidate oral vaccine against LMBV infection in aquaculture.

Early warning system for nocardiosis in largemouth bass (Micropterus salmoides) based on multimodal information fusion

The high-density culture of the recirculating aquaculture system (RAS) makes bacterial and parasitic diseases in fish likely to spread within these systems. Therefore, preventing and controlling the occurrence of fish diseases in RAS is crucial for the future development of aquaculture. However, the current circulating water system lacks early warning measures to prevent and control diseases, resulting in poor accuracy in early warning and detection of diseases. To tackle this challenge, this study introduces an early warning system for largemouth bass (Micropterus salmoides) disease, which is based on You Only Look Once vision 8 (YOLOv8), ByteTrack, Long-Short-Term-Memory(LSTM), and Fuzzy Inference System (FIS). The system utilizes the water quality, surface characteristics, and behavioral traits of diseased fish to predict and prevent disease outbreaks. The system achieved an accuracy of 79.33% for identifying infected body surface features, 80.65% for identifying diseased water quality, and 81.08% for predicting diseased behavior. The experimental results indicate that the early warning system is highly reliable and effective, achieving integrated disease identification accuracy as high as 94.08%. This study enhances the accuracy of early disease warning in fish disease conditions, achieving early warning of nocardiosis in largemouth bass. The study provides crucial technical support for the sustainable and high-quality development of the aquaculture industry.

Comparative evaluation of nutritional quality and flavor characteristics for Micropterus salmoides muscle in different aquaculture systems

To investigate the nutritional quality and flavor characteristics of Micropterus salmoides muscle cultivated in the pond (P), in-pond raceway (IPRS), and industrial aquaponics (ARAS) systems, we comprehensively analyzed texture properties, nutrient compositions, and volatile compounds. Our results revealed firmer flesh in P-cultured fish due to greater hardness and mastication. ARAS fish exhibited lower crude fat but higher crude protein and muscle glycogen. Notably, recirculating aquaculture significantly elevated total amino acids, minerals, and ΣPUFA/ΣSFA ratio, enhancing nutritional value. Pyrazine,2-methoxy-3-(2-methylpropyl)-, and β-Ionone were identified as key flavor compounds. Volatile metabolites in all systems were dominated by woody, herbal, and sweet aroma profiles, with ARAS achieving the highest odor activity value, suggesting improved overall flavor. This study underscores the pivotal role of recirculating aquaculture in enhancing Micropterus salmoides quality, positioning it as a new quality productive force.

Multiplex qPCR development for the simultaneous and rapid detection of largemouth bass virus and infectious spleen and kidney necrosis virus in aquaculture

Largemouth bass virus (LMBV) and infectious spleen and kidney necrosis virus (ISKNV) are both belong to Iridoviridae that cause considerable economic losses in the fish industry. There is no reported literature that can detect these two viruses simultaneously. In this study, we established a multiplex quantitative polymerase chain reaction (qPCR) assay that can specifically and simultaneously detect both LMBV and ISKNV in fish samples. The specificity experiment showed that the method only amplified LMBV and ISKNV but not the other 10 common fish viruses. The slope (m), efficiency (E) and linearity (R2) determined from the generated standard curve were all within the optimal range of qPCR values. The detection limit of the multiplex qPCR assay was as low as 4 copies/μL for LMBV DNA and 7 copies/μL for ISKNV DNA, respectively. The established method exhibited adequate repeatability and reproducibility, and the intra- and inter-assay coefficients of variation were both less than 3 %. The accuracy of the multiplex qPCR method was validated using 229 fish samples and was more precise than that of the conventional PCR assay. In summary, the established multiplex qPCR assay can simultaneously detect LMBV and ISKNV to monitor the risk of infection LMBV and ISKNV and control the disease early.

Effects of Dietary Ursolic Acid on Growth Performance and Intestinal Health of Largemouth Bass (Micropterus salmoides).

This study aimed to investigate the effects of ursolic acid (UA) on the growth performance and intestinal health of largemouth bass (Micropterus salmoides). Four diets were formulated with UA supplementation at 0, 250, 500, and 1000 mg/kg, defined as the control (CON), UA250, UA500, and UA1000, respectively. After an 8-week feeding experiment, the results showed that, in the UA500 group, the final body weight (FBW), weight gain rate (WGR), and specific growth rate (SGR) increased, and the feed conversion ratio (FCR) and hepatosomatic index decreased. Total superoxide dismutase (T-SOD) activity exhibited a significant increase, and malondialdehyde (MDA) content decreased. An intestinal histological analysis revealed an improvement in the intestinal structural integrity of the UA500 group. The mRNA relative expression levels of physical barrier-related genes [occludin, claudin-1, and zonula occluden-1 (zo-1)] were upregulated. The mRNA relative expression of interlenkin 10 (il-10) increased, and the mRNA relative expression of interlenkin 1β (il-1β) and tumor necrosis factor-α (tnf-α) significantly decreased. The abundance of Firmicutes and Proteobacteria decreased, and the abundance of Tenericutes increased. The abundance of Mycoplasma, Cyanobium, and Staphylococcus decreased, while the abundance of Clostridium increased. In conclusion, dietary supplementation of UA significantly enhanced the growth performance and antioxidant capacity of largemouth bass while improving intestinal barrier function through its influence on the abundance of intestinal flora, such as Tenericutes, Firmicutes, and Mycoplasma. Optimal dietary UA levels for largemouth bass were determined to be between 498 and 520 mg/kg based on quadratic regression analyses of WGR, SGR, and FCR or T-SOD and MDA content.

Transcriptome analysis of four types of gonadal tissues in largemouth bass (Micropterus salmoides) to reveal its sex-related genes.

The sex determination system of largemouth bass (Micropterus salmoides, LMB) is XX/XY; however, the underlying molecular mechanisms involved in early sex differentiation, gonadal development, and exogenous hormone-induced sex reversal remain unknown. In this study, LMB at 15days post-hatching (dph) were fed diets containing 20mg/kg of 17α-methyltestosterone (17α-MT) or 30mg/kg of 17β-estradiol (17β-E2) for 60days, respectively. Serum steroid levels, histological observations of the gonads, and identification of sex-specific markers were employed to screen the gonads of 60-day-old normal female fish (XX-F), normal male fish (XY-M), 17β-E2 induced pseudo-female fish (XY-F), and 17α-MT-induced pseudo-male fish (XX-M) for transcriptome sequencing in order to uncover genes and pathway involved in the process of sexual reversal. The results from histology and serum sex steroid hormone analysis showed that both 17α-MT and 17β-E2 were capable of inducing sex reversal of LMB at 15dph. Transcriptome results revealed a total of 2,753 genes exhibiting differential expression, and the expression pattern of these genes in the gonads of XX-M or XY-F resembled that of normal females or males. The male sex-biased genes that are upregulated in XX-M and downregulated in XY-F are referred to as key genes for male reversal, while the female sex-biased genes that are upregulated in XY-F and downregulated in XX-M are referred to as key genes for female reversal. Finally, 12 differentially expressed genes (DEGs) related to male sex reversal were screened, including star2, cyp17a, cyp11b1, dmrt1, amh, sox9a, katnal1, spata4, spata6l, spata7, spata18 and foxl3. 2 DEGs (foxl2a and cyp19a1b) were found to be associated with female sex reversal. The changes in these genes collectively influence the direction of sex differentiation of LMB. Among them, star2, dmrt1 and cyp19a1b with significantly altered expression levels may play potentially crucial role in the process of gender reversal. The expression patterns of 21 randomly selected genes were verified using qRT-PCR which confirmed the reliability and accuracy of the RNA-seq results. These findings not only enhance our understanding of the molecular basis underlying sex reversal but also provide crucial data support for future breeding research on unisexual LMB.

Morphological Analysis of a New Species of Micropterus (Teleostei: Centrarchidae) from Lake Erie, PA, USA.

This previously undescribed species of Micropterus is described from collections in Lake Erie. The species was first recognized by the tri-colored tail of juveniles. This tri-colored tail, the presence of bold parallel lines ventral to the lateral band, and scales in the inter-radial membranes of the dorsal fin distinguish it from Micropterus nigricans. The large mouth that extends past the eye distinguishes it from Micropterus punctulatus.

The effect of dietary full-fat Hermetia illucens larvae meal on growth performance and intestine physiology in largemouth bass (Micropterus salmoides)

The present study aimed to investigate the effects of different inclusion levels of full-fat Hermetia illucens larvae (HI) meal as a protein source on the growth performance, intestinal morphology, health, and microbiota of largemouth bass. Five isonitrogenous and isolipidic diets were formulated by adding HI to replace 0 % (HI0, control), 10 % (HI10), 20 % (HI20), 30 % (HI30) and 40 % (HI40) of fish meal (FM) in diets. Each diet was randomly assigned to triplicate groups of 30 fish per aquarium. Fish were fed two times daily to apparent satiation for 80 days. The results indicated that weight gain rate, specific growth rate and protein efficiency ratio were not appreciably reduced until more than 30 % of the FM protein was replaced with HI. Fish fed HI40 diet had the lowest fatty acid (C18:3, C20:5, C22:6) contents (P < 0.05). Moreover, the villi height was decreased, villi width and goblet cell number in hindgut was increased in the HI40 group compared with the other groups, respectively. Meanwhile, serum diamine oxidase activity, D-lactate and endotoxin contents increased markedly as the proportion of HI increased (P < 0.05). Notably, the increased dietary HI levels down-regulated the mRNA expression levels of cldnd1b and ocel1 in intestine. Higher malondialdehyde content and down-regulated expression of sod and gpx1a in the intestine were also observed in the HI40 group. Accordingly, the increased dietary HI levels upregulated the expression of intestinal pro-inflammatory cytokines (tumor necrosis factor-α and interleukin-1β) and down-regulated anti-inflammatory cytokines (transcriptional growth factor-β1 and interleukin-10) (P < 0.05). In addition, the abundance of both intestinal Lactobacillus and Streptococcus increased significantly, while the abundance of Cetobacterium decreased in the HI20 group (P < 0.05). Broken-line model analysis based on weight gain rate against dietary HI replacement level indicated that the optimum replacement level was 26.79 %. However, including too high proportion of HI could induce intestinal dysbiosis, impair the intestine physical barrier, and finally reduced growth of Micropterus salmoides.

Resilience to changes in salinity and predator diversity in representative Gulf of Mexico estuarine fish predator-prey interactions

Predators strongly influence ecological communities and subsequent ecosystem function by directly consuming prey individuals and indirectly by inciting alterations in prey behavior, termed non-consumptive effects (NCEs). Gulf of Mexico estuaries support complex food webs structured by numerous species interactions maintained in constant environmental flux from variation in salinity. Environmental variation presents a source of physiological stress for estuarine fish and plays a role in their distributions and subsequent interactions. Here, we present the results of a mesocosm experiment examining if acute changes in salinity disrupt NCEs of different predators on estuarine prey. We exposed Gulf killifish (Fundulus grandis) to visual and/or olfactory cues from a common estuarine predator, red drum (Sciaenops ocellatus), and from a freshwater predator that is a transient species in lower portions of estuaries, largemouth bass (Micropterus salmoides), under either decreasing, constant, or increasing salinity. Killifish decreased shoal size and movement in response to olfactory cues or both visual and olfactory cues compared to when they were exposed to no cues or visual cues, demonstrating variable perceived risk dependent on cue type. Behavioral response did not vary by predator species, implying a generalized response to different fish predators. Prey did not change behavior when exposed to decreasing salinity compared to constant salinity. However, prey movement increased with increasing salinity, indicating that salinity changes may provide cues to search for different habitats instead of a stressor. Our experiment indicates that estuarine predator-prey interactions may be resilient to acute salinity changes given the broad tolerances of euryhaline species.

Polystyrene nanoplastics significantly facilitate largemouth bass ranavirus infection of host cells

Novel pollutants nanoplastics (NPs) are widely distributed in aquatic environments and may pose a health threat to aquatic organisms. Notably, the contribution of NPs to the occurrence of viral diseases in aquatic animals remains largely uncertain. In this study, the effects of polystyrene nanoplastics (PS-NPs) on Largemouth bass ranavirus (LMBV)-infected MsF cells were investigated. MsF cells took up PS-NPs in a time- and dose-dependent manner and significantly affect cell viability at an exposure concentration of 500 μg/mL. Western blot and qPCR assays indicated that exposure to PS-NPs accelerated LMBV replication in MsF cells. PS-NPs act synergistically with LMBV to disrupt the cellular antioxidant system, as evidenced by increased ROS production and decreased mRNA levels of antioxidant-associated genes. Furthermore, PS-NPs was found to exacerbate LMBV-induced inflammatory responses, as demonstrated by disturbed expression of inflammation-related factors. In addition, our results suggest that PS-NPs reduce IFN production by inhibiting the expression of molecules related to the cGAS-STING signaling pathway, thereby promoting viral replication. Collectively, our findings suggest the potential threat of NPs to infectious diseases caused by freshwater fish viruses and provide new insights for fish disease prevention and control.

Production and evaluation of three kinds of vaccines against largemouth bass virus, and DNA vaccines show great application prospects

Largemouth bass virus (LMBV) infections has resulted in high mortality and economic losses to the global largemouth bass industry and has seriously restricted the healthy development of the bass aquaculture industry. There are currently no antiviral therapies available for the control of this disease. In this study, we developed three types of vaccine against LMBV; whole virus inactivated vaccine (I), a subunit vaccine composed of the major viral capsid protein MCP (S) as well as an MCP DNA vaccine(D), These were employed using differing immunization and booster strategies spaced 2 weeks apart as follows: II, SS, DD and DS. We found that all vaccine groups induced humoral and cellular immune responses and protected largemouth bass from a lethal LMBV challenge to varying degrees and DD produced the best overall effect. Specifically, the levels of specific IgM in serum in all immunized groups were elevated and significantly higher than those in the control group. Moreover, the expression of humoral immunity (CD4 and IgM) and cellular immunity (MHCI-α) as well as cytokines (IL-1β) was increased, and the activity of immunity-related enzymes ACP, AKP, LZM, and T-SOD in the serum was significantly enhanced. In addition, the relative percent survival of fish following an LMBV lethal challenge 4 weeks after the initial immunizations were high for each group: DD(89.5 %),DS(63.2 %),SS(50 %) and II (44.7 %). These results indicated that the MCP DNA vaccine is the most suitable and promising vaccine candidate for the effective control of LMBV disease.

Role of Cholecystokinin (cck) in Feeding Regulation of Largemouth Bass (Micropterus salmoides): Peptide Activation and Antagonist Inhibition.

This study investigated the role of cholecystokinin (cck) in the feeding regulation of largemouth bass (Micropterus salmoides) via peptide activation and antagonist inhibition. The results show that the cck gene was expressed in various tissues, with the highest expression level occurring in the brain. Feeding, continuous feeding, and refeeding after fasting could significantly improve the mRNA levels of cck in the brain. Moreover, the activation of cck via injecting an exogenous CCK peptide could inhibit feed intake by regulating the mRNA levels of anorexigenic and feed-promoting factors in the brain and intestine. Furthermore, the CCK peptide reduced feed intake; however, the presence of an antagonist (Ly225910-CCK1R and devazepide-CCK2R) could reverse this effect through regulating the mRNA levels of anorexigenic and feed-promoting factors in the brain and intestine. Treatment with devazepide + CCK (CCK2R) reversed feed intake more effectively than Ly225910 + CCK (CCK1R) treatment. In summary, cck could regulate the feed intake of largemouth bass through regulating feeding-related genes in the brain and intestine. In addition, cck required binding with the receptor to inhibit feed intake more effectively in largemouth bass, and the binding effect of CCK1R was better than that of CCK2R.

PI3KR1 and AKT1 in largemouth bass (Micropterus salmoides): molecular cloning, characterization, and its involvement in the alleviation of hepatic glycogen deposition caused by insulin inclusion in vitro.

In this study, the full-length cDNA sequences of the phosphatidylinositol-3-kinase p85 alpha (PI3KR1) and serine/threonine kinase 1 (AKT1) genes in largemouth bass (Micropterus salmoides) were obtained using the rapid amplification of cDNA ends (RACE) method. Sequence analysis revealed that the cloned sequences of PI3KR1 and AKT1 are 4170 bp and 3672 bp in length, with open reading frames (ORFs) of 1389 bp and 1422 bp encoding 462 and 473 amino acids, respectively. Sequence alignment and evolutionary tree analysis indicated their close relationship to other teleosts, especially those with similar feeding habits. Tissue distribution demonstrated widespread distribution of both genes in various tissues, with the highest abundance in the liver. Further results found that the upregulation of the expression of p-PI3KR1, p-AKT1, p-FoxO1, and GLUT2 proteins by insulin, while suppressing the expression of the total FoxO1 protein, effectively triggers a significant activation of the PI3KR1-AKT1 insulin signaling pathway. Meanwhile, the mRNA levels of the key glycolytic genes, including glucokinase (gk), pyruvate kinase (pk), and phosphofructokinase liver type (pfkl), have been enhanced evidently. In contrast, the expression of gluconeogenic genes such as phosphoenolpyruvate carboxykinase (pepck), glucose-6-phosphatase catalytic subunit (g6pc), and fructose-1,6-bisphosphatase-1 (fbp1) has been notably down-regulated. In addition, insulin treatment promoted the phosphorylation of glycogen phosphorylase (PYGL) and the dephosphorylation of glycogen synthase (GS), and the glycogen content in the insulin-treated group was remarkably reduced compared to the control group. Overall, our study indicates that the activation of PI3KR1-AKT1 insulin signaling pathway represses the hepatic glycogen deposition via the regulation of glycolysis and gluconeogenesis, which provides some new insights into nutritional strategy to effectively regulate the glucose metabolism in carnivorous fish.

Threonine supplementation stimulates immune, antioxidant and liver functions of largemouth bass, Micropterus salmoides

Threonine is an essential amino acid required in the diets for regular growth of fishes, but information is inadequate regarding the effects of threonine on immunity and health status of many aquaculture species. In the present study, a total of 360 juvenile largemouth bass, Micropterus salmoides (19.0 ± 0.1 g) were divided into six experimental groups, and fed diets supplemented with varying levels of crystalline L-threonine at 0 g kg−1 (control), 2.5 g kg−1 (Thr-2.5), 5.0 g kg−1 (Thr-5.0), 7.5 g kg−1 (Thr-7.5), 10.0 g kg−1 (Thr-10.0) and 12.5 g kg−1 (Thr-12.5) for eight weeks. The results revealed that white blood cell count (P = 0.024) and albumin content (P = 0.006) in fish were significantly modulated by the dietary threonine, with the highest levels recorded in fish fed diets Thr-5.0 and Thr-12.5, respectively. White blood cell increased with dietary threonine levels up to Thr-5.0, then decreased thereafter. The other hematological variables such as red blood cell (P = 0.571), hemoglobin (P = 0.259), hematocrit (P = 0.985), mean corpuscular volume (P = 0.631), mean corpuscular hemoglobin (P = 0.280) and mean corpuscular hemoglobin concentration (P = 0.691) remained unchanged as compared to the control group. Serum lysozyme increased (P = 0.000) with increasing levels of threonine up to 5.0 g kg−1. Fish receiving diet Thr-2.5 had relatively higher (P = 0.000) immunoglobulin M and the level decreased when fed with increasing levels of threonine. The activities of superoxide dismutase (P = 0.008) and malondialdehyde (P = 0.005) were elevated at 10.0 g kg−1 and 12.5 g kg−1 supplementation levels, respectively. Moreover, diets Thr-5.0 and Thr-10.0 induced lower serum alanine aminotransferase (P = 0.011) and aspartate aminotransferase activities (P = 0.000) in fish. These results suggest that threonine supplementation led to a positive effect on the hematology, humoral immunity, antioxidant capacity and liver function enzyme activities of economically important largemouth bass. Therefore, threonine has a clear role in fish nutrition and is important in formulating nutritionally balanced feeds.

A Modified Calculation of the Withdrawal Time and a Risk Assessment of Enrofloxacin in Micropterus salmoides after Its Ad Libitum Administration via Medicated Feed in the Commercial Aquaculture.

The present study investigated the residue depletion and WTs of EF and its main metabolite, ciprofloxacin, in largemouth bass after ad libitum administration in commercial fish farming based on statistical approaches. Samples collected at pre-determined time points were assessed using high-performance liquid chromatography. If the concentrations of medicine were less than the quantitative limit, they were set to be half of the limit of quantitative. The terminal elimination of the target compound was assumed to fit a one-compartment model. The statistical methods of Bartlett's test and Cochran's test were used to inspect the homogeneity of the log-transformed data. The lack-of-fit test and F-test were used to check the linearity of the regression line. Outliers were assessed using standardized residuals. The final WT was estimated using the 95% percentile with a 95% confidence level. The WTs of EF were calculated to be 46, 29, 33, 46, and 20 days for the muscle + skin, plasma, gill, kidney, and liver, respectively. After the risk assessment, the values of the hazard quotient were calculated to be far less than 1, indicating that the risk of residual EF was particularly low in the edible tissues of largemouth bass after medicine depletion for various WTs.