Largemouth Research Articles

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.

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.

Analysis of Differential Alternative Splicing in Largemouth Bass After High Temperature Exposure.

Temperature is one of the critical factors affecting the physiological functions of fish. With ongoing global warming, changes in water temperature have a profound impact on fish species. Alternative splicing, being a significant mechanism for gene expression regulation, facilitates fish to adapt and thrive in dynamic and varied aquatic environments. Our study used transcriptome sequencing to analyze alternative splicing in largemouth bass gills at 34 °C for 24 h. The findings indicated an increase in both alternative splicing events and alternative splicing genes after high temperature treatment. Specifically, the comparative analysis revealed a total of 674 differential alternative splicing events and 517 differential alternative splicing genes. Enrichment analysis of differential alternative splicing genes revealed significant associations with various gene ontology (GO) terms and KEGG pathways, particularly in immune-related pathways like necroptosis, apoptosis, and the C-type lectin receptor signaling pathway. These results emphasize that some RNA splicing-related genes are involved in the response of largemouth bass to high temperatures.

Hatch timing of largemouth bass: implications for recruitment at the Northern edge of their native range

Climate-related shifts in hatch timing could mean that age-0 largemouth bass Micropterus salmoides in north temperate lakes reach larger sizes and experience higher survival, which may contribute to increased prevalence of this species in many lakes. However, information on age-0 largemouth bass life history is lacking for these lakes. We estimated hatch dates, daily growth rates (DGR), and length-based probability of piscivory of age-0 largemouth bass in Wisconsin lakes to: (1) provide baseline data on early life history; (2) compare hatch timing between years with different spring temperature regimes, and (3) project how shifts in hatch timing might influence total length (TL) distributions of age-0 bass if mean DGR remained constant. Most age-0 largemouth bass (>90%) collected from ten Wisconsin lakes (N = 746) hatched between 23 May and 24 June during 2012 and 2013 and did not switch to piscivory during their first summer. Prevalence of positive correlations (16 of 24 lake-year pairings) between TL in and age indicates hatch timing may influence TLs attained by age-0 largemouth bass in August in some lake-years. Mean daily water temperatures in May 2012 were 3.1 °C warmer than in May 2013 for the five of the six lakes where hatch dates were estimated in both years. On average, earliest and median hatch dates for age-0 largemouth bass in these six lakes were 10–11 d earlier in 2012 than in 2013 and hatch duration was approximately 8 d longer in 2012. Despite differences in hatch timing, mean DGR was relatively consistent (range = 0.61–0.74 mm/d) between lakes and years. Simple simulations suggest that earlier hatch dates could result in more age-0 largemouth bass reaching TLs associated with piscivory and overwinter survival by the end of their first summer if growth rates did not change, which could translate to higher recruitment.

Study on the immune enhancers against &lt;i&gt;Micropterus salmoides&lt;/i&gt; rhabdovirus infection

Micropterus salmoides rhabdovirus (MSRV) is one of the most serious pathogens harming M. salmoides juvenile, which had brought huge economic losses to farming industry. Studies involving candidate genes to the clinical diseases, however, are limited. In this study, the viral target and clinical manifestation of MSRV on M. salmoides juvenile were analyzed, and the protective effects of a single immune enhancer and a compound immune enhancer were evaluated. The results showed that the brain, liver, intestine and muscle of M. salmoides showed obvious lesions after infection with MSRV. The relative expression levels of nucleoprotein (N) and matrix protein (M) genes showed a trend of increasing at first and then decreasing and reached the peak in each tissue at 36 h post-infection. The mortality rate of M. salmoides was over 90% after 7 days of MSRV infection. The immune enhancers containing free nucleotides and Astragalus polysaccharide added to the diet effectively inhibited the replication of N and M genes in M. salmoides and increased the survival rate by 25% to 28%. This study provided basic data and theoretical reference for the analysis of the pathological mechanism and prevention and treatment of MSRV.

Germplasm Resources Evaluation of Cultured Largemouth Bass (Micropterus salmoides) in China Based on Whole Genome Resequencing.

Background: Largemouth bass (Micropterus salmoides), a valuable freshwater fish species, has experienced significant genetic decline in China due to prolonged domestic breeding and limited introduction of new genetic material. It is necessary to have a comprehensive understanding of the genetic status of largemouth bass populations in China. Method: In this study, we conducted population genetic analyses on nine cultured largemouth bass populations using whole genome resequencing. Results: A total of 3.23 Tb of clean bases were generated, with average Q20 and Q30 values of 98.17% and 94.25%, respectively, and 2,140,534 high-quality SNPs were obtained. Relatively high genetic diversity was observed across all populations. Combined with linkage disequilibrium (LD) patterns, the Wanlu (WL) population possessed the highest genetic diversity, and the Longyou (LY) population possessed the lowest genetic diversity. Additionally, population structure analyses, including pairwise F-statistics, phylogenetic trees, PCA, and admixture analysis, revealed significant genetic differentiation, particularly between the WL, LY, and other 7 populations, while also indicating the occurrence of a common admixture event. Finally, TreeMix inferred migration events from the WL to the Chuanlu (CL) population and from the Taiwan breeding population (TWL) to the Guanglu (GL) population. Conclusions: These findings provide a critical foundation for developing conservation and breeding strategies for largemouth bass in China.

Curcumin is an efficacious therapeutic agent against Chilodonella uncinata via interaction with tubulin alpha chain as protein target

Chilodonella, a parasitic ciliate that infects both cold water and warm water fish, can impede the growth of juvenile fish and cause considerable economic losses globally to freshwater aquaculture. In this study, the parasite was collected from both the gills and zygotes of largemouth bass (Micropterus salmoides). Isolated from diseased fish, the parasites were identified as Chilodonella uncinata based on morphological features and genetical diagnostic characterization using the partial small subunit ribosomal RNA gene. To develop an effective approach to treat chilodonellosis caused by C. uncinata in largemouth bass farming, we first developed an in vivo culture model for propagating C. uncinate and thus could use for morphological characterization, molecular analyses and antiparasitic drug screening. Curcumin was successfully identified as an efficacious anti-C. uncinata agent from 26 phytochemical compounds. When administered at a concentration of 6 mg/L, curcumin not only completely cured infected largemouth bass but also shielded uninfected fish from C. uncinata infections. The 24 h median effective concentration (EC50) of curcumin against C. uncinata was 3.098 mg/L. Remarkably, the 96 h median lethal concentration (LC50) of curcumin against largemouth bass was determined to be 17.143 mg/L, approximately 5.533 times higher than EC50. The mechanism of action of curcumin was investigated by the cellular thermal shift assay, demonstrating that tubulin alpha chain was the binding target for curcumin. Moreover, SEM investigations further provided morphological evidence suggesting that curcumin induces parasite demise by disrupting the parasite's body surface and subsequently infiltrating its interior. These findings collectively emphasize the potential of curcumin as a safe and effective therapeutic agent for controlling C. uncinata in aquaculture.

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.

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.

Chlorogenic Acid Plays an Important Role in Improving the Growth and Antioxidant Status and Weakening the Inflammatory Response of Largemouth Bass (Micropterus salmoides).

This experiment evaluated the function of chlorogenic acid (CGA) in the growth, health status, and inflammation of largemouth bass (Micropterus salmoides). Over eight weeks, CGA supplementation was designed at five levels: 0, 60, 120, 180, and 240 mg/kg. The 180 and 240 mg/kg CGA-supplemented groups showed significant improvements in the FBW, SGR, and WGR compared to the control group (0 mg/kg) (p < 0.05). All the CGA-supplemented groups exhibited a significant reduction in the FCR (p < 0.05), with the 180 mg/kg CGA group showing the lowest FCR. Nonetheless, there were no appreciable differences in the plasma concentrations of TP, ALT, or AST among the treatments (p > 0.05). Compared to the control group, the 180 mg/kg CGA group exhibited significantly lower TC and TG levels (p < 0.05). The ALP levels showed no significant differences from the control group (p > 0.05). In terms of antioxidant parameters, CGA supplementation considerably reduced the MDA content (p < 0.05) and increased the GSH levels, while decreasing the CAT, SOD, and GPx activity levels Meanwhile, CGA supplementation resulted in reduced mRNA levels of SOD, CAT, Nrf2, Keap1, and NF-κB compared to the control group. In contrast, the mRNA levels of GPx, IL-8, TLR2, and RelA were elevated in the liver. Our findings indicated that CGA supplementation improved the growth performance and antioxidant status and weakened the inflammatory response of largemouth bass. These findings suggest that CGA could be a valuable dietary supplement for enhancing the health and growth of this species.

Effects of high α-linolenic acid transgenic rapeseed oil diet on growth performance, fat deposition, flesh quality, antioxidant capacity, and immunity of juvenile largemouth bass (Micropterus salmoides).

Omega-3 long-chain polyunsaturated fatty acid (n-3 LC-PUFA) increases in aquatic products contributes to improving meat quality, thereby positively impacting human health. Different from marine fish which primarily obtain n-3 LC-PUFAs directly from zooplankton and algae, freshwater fish mainly utilize dietary linolenic acid (ALA) as a substrate to synthesize n-3 LC-PUFAs. Our team has successfully created a transgenic rapeseed oil (TRO) with high ALA content. Therefore, we here assessed the impacts of four different diets (LR, low-fat rapeseed oil (RO) diet; HR, high-fat RO diet; LTR, low-fat TRO diet; HTR, high-fat TRO diet) on growth performance, lipid accumulation, fatty acid composition, antioxidant capacity, immunity and serum biochemical indexes of juvenile largemouth bass (Micropterus salmoides), an economically valuable freshwater fish. The results showed no significant difference in survival rate among the four dietary groups. No significant differences in body weight gain and final weight were found between the LR and LTR groups, as well as between HR and HTR groups. No matter if it was a high-fat or low-fat diet, compared with the RO diet, TRO diets significantly increased the content of n-3 LC-PUFA, improved meat quality, effectively alleviated lipid accumulation in livers and muscles of juvenile largemouth bass. In addition, using high-fat diets, TRO diet improved the antioxidant capacity and immune ability of juvenile largemouth bass, thereby promoting the overall health of fish. This study provides novel insights for fish feed formulation optimization from the perspective of genetically modified feed ingredients, and high-quality aquatic products for human consumption.

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.

Climate change and non-native species in the Spanish Network of National Parks

AbstractThe Iberian Peninsula is a primary entry point for non-native species (NNS) into Europe via maritime routes, and is a significant tourist destination. This positions the highly diverse Spanish National Parks at high risk from invasive species, necessitating proactive adaptation and mitigation strategies. We present a comprehensive analysis of the risks posed by NNS to the network of 15 continental and marine National Parks in Spain under climate change, aiming to align management strategies with international Global Biodiversity Framework (GBF) targets. We identified 200 NNS across the network of National Parks, including 78 listed in national NNS regulations. Park managers helped identify 22 priority NNS, including the water hyacinth, American mink, Cape fig and wakame, among others. Over half of the 22 priority NNS (55%) were classified as having a “Major” impact on native biodiversity according to EICAT standards, with another 23% considered “Massive”. Distribution models suggest that rising minimum temperatures could enable NNS to expand in altitude within the parks, particularly in high-mountain parks. Species like the barbary sheep, water hyacinth and largemouth bass may particularly benefit from global warming. Our findings prioritize national parks most vulnerable to the double threat posed by climate change and invasive species, such as Islas Atlánticas, Doñana and Archipelago de Cabrera. We conclude that, in order to progress towards achieving GBF goals, it is essential to: (i) coordinate NNS management efforts across administrations (national and regional), (ii) integrate resources and expertise in a unified strategy against invasion across the network and (iii) enhance public awareness about the risks of introduction and impact of NNS.

Elastic Bands Improve Oral Appliance Treatment Effect on Obstructive Sleep Apnoea: A Randomised Crossover Trial.

Oral appliances (OAs) that limit mouth opening during sleep, such as monobloc appliances, have shown superior treatment effects in subgroups of patients with obstructive sleep apnoea. The application of elastic bands on bibloc appliances may resemble these benefits. The primary objective was to investigate if application of elastic bands to bibloc appliances improves treatment success (> 50% reduction of respiratory event index (REI)), in addition to other subjective variables. Furthermore, we aimed to identify variables predicting the need for elastic bands in OA treatment. Included patients (n = 69) were randomly assigned to OA treatment with or without elastic bands. After 3 weeks, treatment effect was investigated with home respiratory polygraphy and questionnaires. Thereafter, patients changed treatment modality, with identical follow-up regime. Statistical analyses were performed using Student's t-test and Pearson's chi-squared test to investigate differences between the two treatment modalities, and logistic regression analysis was conducted to investigate variables tentatively associated with treatment success. Based on REI, the success rate with OA treatment was in favour of elastic bands (53.9% vs. 34.6%, p = 0.002). Male sex and larger maximum mouth opening were identified as predictors for increased treatment success with elastic bands. The main benefit with elastic bands seemed to be greater reduction of REI when supine. However, patients seem to prefer OA without elastic bands. Elastic bands improved OA treatment effect by reducing the REI in supine position. Patient groups that seemed to benefit from elastic bands in OA treatment were men with large maximum mouth openings.

Connection between the gut microbiota of largemouth bass (Micropterus salmoides) and microbiota of the aquaponics system environment.

The significant role played by the gut microbiota in fish growth, development, immunity, and overall health has been widely established. Nevertheless, there remains a lack of clarity regarding the interaction and origin between the environmental microbiota and the gut microbiota of aquaculture species within the aquaponics coupling system. Thus, we conducted an analysis of the gut microbiota of largemouth bass (Micropterus salmoides) obtained from an indoor enclosed circulating water aquaponics coupling system located in greenhouses in northern China. Additionally, we examined the microbiota of the fish pond water and tomato rhizosphere soil using high-throughput sequencing of the 16S rRNA gene. Our results demonstrated significant differences in the compositions of fish pond water, rhizosphere soil, and the gut microbiota of largemouth bass. Moreover, these compositions changed throughout the culture period. Approximately 11.99% of the bacterial composition in the gut microbiota of largemouth bass could be attributable to the rhizosphere soil microbiota, while 62.01% of the bacterial composition could be attributable to the fish pond water microbiota. However, the proportion of bacteria in the gut microbiota from the fish pond water microbiota remained respectively 40.90% and 56.15% in May and September, which increased markedly to 88.97% in July. Similarly, the proportion of bacteria in the pond water microbiota from the tomato rhizosphere soil microbiota were respectively 0% and 8.95% in samples collected in May and September, which increased markedly to 69.26% in July, and the proportion of bacteria in the gut microbiota from the tomato rhizosphere soil microbiota were respectively 0.07% and 0% in samples collected in May and September, which increased to 0.45% in July. The research results offer essential insights into the interactions and origins of environmental microbiota and gut microbiota in the aquaponics system of cultured fish. This knowledge could enhance green aquaponics practices for largemouth bass.

Dietary lecithin attenuates adverse effects of high fat diet on growth performance, lipid metabolism, endoplasmic reticulum stress and antioxidant capacity in the intestine of largemouth bass (Micropterus salmoides)

This study was conducted to investigate the effects of dietary lipid and lecithin levels on growth performance, lipid metabolism, endoplasmic reticulum stress and antioxidant capacity in intestinal tissues of largemouth bass (Micropterus salmoides). Five experimental diets include the control (10.67 % lipid, normal dietary lipid without extra lecithin addition), 1.0 g/kg lecithin diet with normal dietary lipid level (Lec diet, 10.94 % lipid), high fat diet without extra lecithin addition (HFD, 18.65 % lipid), and HFD supplemented with 1.0 g/kg and 2.0 g/kg lecithin (HFD + Lec1 and HFD + Lec2 diets, respectively). Largemouth bass (initial body weight: 5.39 ± 0.04 g/fish) were fed five diets for 10 weeks. Dietary lecithin alleviated the growth retardation and intestinal damage induced by HFD. HFD-induced increase of whole body and intestinal crude lipid contents and decline of intestinal poly-unsaturated fatty acids content were also alleviated by dietary lecithin addition. Dietary lecithin alleviated the increase of TG content, activities of lipogenic enzymes (G6PD, 6PGD, ME, ICDH and FAS), mRNA expression of lipogenic genes (g6pd, 6pgd, fas, accα, dgat1, dgat2 and srebp1) and protein expression of Srebp1, and downregulation of mRNA expression of lipolytic gene cpt1) and protein expression of Pparα induced by HFD. Lecithin addition mitigated the up-regulation of mRNA expression of lipid absorption genes (fabp2, fatp4, sr-1b and npc1l1), and the down-regulation of mRNA expression of chylomicron assembly- and secretion-relevant genes (mttp and acat2) and proteins (Mttp, Apob and Sar1b), chylomicron components (TG, phosphatidylcholine and apolipoprotein) and MTTP activity induced by HFD. Compared with HFD, HFD + Lec1 diet significantly decreased the mRNA expression of endoplasmic reticulum (ER) stress genes (grp94, grp78, calr, chop, ire1α and xbp1) and Grp78 protein expression. Compared with HFD, the activities of antioxidant enzymes (CAT, T-SOD and GPx) and mRNA expression of genes (sod1, cat, gpx1 and nrf2) were significantly increased but MDA content and keap1 mRNA expression were significantly decreased in HFD supplemented with 1.0 g/kg and 2.0 g/kg lecithin. These results indicated that dietary lecithin supplementation increased growth rate, improved lipid metabolism, relieved ER stress, and enhanced antioxidant capacity, thereby alleviating negative effects of HFD on the function and health of intestinal tract of largemouth bass. Statement of relevanceOur results found that dietary addition of lecithin has obvious merits in alleviating negative effects of HFD on the intestinal function and health, which provided good basis for lecithin addition in aquafeeds.

Optimal conditions for cryopreservation by vitrification of largemouth bass (Micropterus salmoides) embryos

The largemouth bass (Micropterus salmoides) is one of the important freshwater aquaculture species in the world. However, due to limitations on introduction scale, high-density farming, inbreeding, and species hybridization, the germplasm resources of largemouth bass face threats such as degradation and susceptibility to diseases. Therefore, it is urgent to conduct research on the conservation of its original and good germplasm resources. We optimized the conditions of cryopreservation to vitrify and revive largemouth bass embryos, including the mixing ratio of cryoprotectants, embryo stage, equilibration step and temperature, and washing regent. The results showed that the least toxic single, binary, and ternary mixed permeating cryoprotectants were PG, PM (PG: MeOH = 2:1), and PMD (PM: DMSO = 3:1), respectively. The least toxic non-permeating cryoprotectant was 5 % glucose. The optimal vitrification solution selected was PMDG (30 % PMD + 5 % glucose) with an 80.67 % survival rate of embryos. Embryos at the heartbeat stage exhibited strong tolerance to the PMDG solution, which is the optimal embryo stage for cryopreservation. During the equilibration process, either the five-step equilibration method or pre-cooling the cryoprotectant to 4°C could reduce its toxicity. During the washing process, a 0.125 mol·L−1 sucrose solution yielded the best results. Based on the optimized conditions, 650 embryos at the heartbeat stage were subjected to cryopreservation by vitrification, resulting in a total of 350 intact transparent eggs, two of which hatched successfully. The results provide a reference for further improving the efficiency of cryopreservation by vitrification of largemouth bass and other fish species.

Genome-wide association study for growth traits with 1066 individuals in largemouth bass (Micropterus salmoides).

The largemouth bass is a native species of North America that was first introduced to mainland China in the 1980s. In recent years, it has been extensively farmed in China due to its high meat quality and broad adaptability. In this study, we collected growth trait data from 1,066 largemouth bass individuals across two populations. We generated an average of approximately 7× sequencing coverage for these fish using Illumina sequencers. From the samples, we identified 2,695,687 SNPs and retained 1,809,116 SNPs for further analysis after filtering. To estimate the number of genome-wide effective SNPs, we performed LD pruning with PLINK software and identified 77,935 SNPs. Our GWAS revealed 15 SNPs associated with six growth traits. We identified a total of 24 genes related to growth, with three genes-igf1, myf5, and myf6-directly associated with skeletal muscle development and growth, located near the leading SNP on chromosome 23. Other candidate genes are involved in the development of tissues and organs or other physiological processes. These findings provide a valuable set of SNPs and genes that could be useful for genetic breeding programs aimed at enhancing growth in largemouth bass.

Palmatine as a potent immunomodulator: Enhancing resistance to Micropterus salmoides rhabdovirus in largemouth bass through innate immune activation and viral suppression

Micropterus salmoides rhabdovirus (MSRV) poses a significant threat to aquaculture, causing substantial economic losses. In this study, we evaluated the antiviral efficacy and immunomodulatory potential of palmatine, a plant-derived monomer, against MSRV infection in largemouth bass. Our results demonstrated that palmatine significantly inhibited MSRV replication, with a reduction in viral nucleoprotein expression by 85 % at a safe concentration. Additionally, palmatine pre-treatment of EPC cells enhanced their antiviral capacity, with a maximum inhibition rate of 82 % following 24 h pre-incubation. Palmatine also effectively reduced MSRV-induced cytopathic effects, protecting cellular integrity and maintaining mitochondrial membrane potential. In vivo studies revealed that palmatine immersion at 80 mg/L was non-toxic and significantly suppressed MSRV replication in largemouth bass, increasing survival rates by 53 % over 15 d. Furthermore, palmatine pre-treatment enhanced the fish's resistance to MSRV, with a 78 % inhibition rate of viral replication and a 46 % increase in survival rate. Mechanistically, palmatine activated key immune genes, including IRF3, IRF7, and IFN, indicating its role in boosting innate immune responses. The compound also reduced horizontal transmission of MSRV in a cohabitation model, decreasing viral spread by up to 78 % over nine days. These findings highlight palmatine's potential as a small-molecule immunomodulator in aquaculture, offering a sustainable approach to disease management and enhancing fish health and welfare. Integrating palmatine into fish diets as an immunostimulant could provide a continuous, proactive defense against viral outbreaks, promoting more resilient and sustainable aquaculture practices.