Diseases In Aquaculture Research Articles

Effects of dietary probiotic (Clostridium butyricum I9, C. butyricum G15, or Paraclostridium bifermentans X13) on growth, digestive enzyme activities, immunity, and intestinal microbiota of Pacific white shrimp (Penaeus vannamei)

Pacific white shrimp (Penaeus vannamei) is one of the most productive and economically important species globally. However, the development and continuous expansion of the farming scale led to an increase in the risk of disease occurrence in shrimp farming. The application of probiotics as an effective method for controlling diseases in aquaculture has been widely considered. In shrimp farming, several probiotics have been used and shown benefits to the health of the host. To diverse the sources of bacterial species as probiotics in shrimp farming, in this study, we aimed to elucidate the effects of dietary probiotics (Clostridium butyricum I9 (I9), Clostridium butyricum G15 (G15), or Paraclostridium bifermentans X13) on the growth, immune response and intestinal microbiome of white shrimp. Shrimps were fed with diets containing either phosphate-buffered saline (PBS), I9 (107 CFU/g feed), G15 (107 CFU/g feed), or X13 (107 CFU/g feed) for 30 days and followed by the challenge with Vibrio parahaemolyticus (Vp). The results showed that the survival rate, body weight gain, and special growth rate of shrimps in the I9, X13, and G15 groups significantly increased, compared to the PBS. The supplementation of probiotics increased the content of short-chain fatty acids and effectively maintained the normal morphology and structure of the intestinal tract and hepatopancreas. The I9, X13, or G15 groups showed a positive change in the diversity and abundance of gut bacteria. There was a significant up-regulation of CTL, SOD, proPO, Crustin, PEN2-4, and ALF1-3 genes in shrimps in the I9, X13, and G15. Additionally, dietary probiotics significantly increased the survival rate, maintained the intestinal structure, promoted the activities of SOD, AKP, ACP, and T-AOC enzymes, and reduced the level of MDA in shrimps after Vp infection. In conclusion, dietary supplementation of I9, G15, or X13 improved the growth, immunity, and disease resistance of Pacific white shrimp, providing a scientific basis for shrimp farming.

Mucosal Exosome Proteomics of Hybrid Grouper Epinephelus fuscoguttatus♀ × E. lanceolatus♂ Infected by Pseudomonas plecoglossicida

Pseudomonas plecoglossicida infection, which causes visceral white spot disease, is a significant and economically devastating disease in aquaculture. In this study, we investigated the impact of bacterial infection on the protein composition of exosomes derived from the surface mucus of the hybrid grouper Epinephelus fuscoguttatus♀ × E. lanceolatus♂. Two hundred healthy fish were randomly separated into challenge and control groups. Fish from the challenge group received 103 CFU/g of the bacterial pathogen P. plecoglossicida via intraperitoneal injection, while sterile PBS was used as a negative control. After injection, the mucus was collected and the exosomes were extracted for proteomic analysis. The results of proteomic analysis revealed that P. plecoglossicida infection significantly increased the levels of innate immune proteins, including lysosomal and peroxisomal proteins, within the exosomes. Furthermore, the CAD protein was found to play a pivotal role in the protein interaction networks involved in the response to P. plecoglossicida infection. Intriguingly, we also observed a significant increase in the levels of metal-binding proteins within the exosomes, providing important evidence of nutritional immunity on the surfaces of the fish hosts. Notably, several proteins, such as plasma kallikrein, Annexin A5, eukaryotic translation initiation factor 3 subunit M, and S-methyl-5-thioadenosine phosphorylase, exhibited a remarkable increase in abundance in exosomes after infection. These proteins show promising potential as noninvasive biomarkers for the diagnosis of visceral white spot disease. The study contributes to the understanding of the host response to P. plecoglossicida infection and may aid policymakers in implementing appropriate intervention measures for effective risk management of this devastating disease.

Assessing the Feasibility of Sustainable Aquaculture for Common Snook Centropomus undecimalis

ABSTRACTCommon Snook (Centropomus undecimalis) is widely distributed across the tropical Atlantic Coasts and has a significant economic impact. This review aims to assess the knowledge status of common snook, contributing significantly to the development of sustainable aquacultural practices. The review was conducted using Web of Science and Google Scholar to identify scientific articles analysing the biology and ecology, the status of snook fisheries and developments in aquaculture production. Researchers in the USA, Mexico and Brazil have conducted 37.95%, 25.52% and 26.21% of published research, respectively, focusing mainly on reproduction in natural environments, status of fisheries and aquaculture production. From an environmental perspective, it is essential to understand the factors impacting C. undecimalis populations. Climate change effects and human alterations to river courses pose significant threats. In addition to fishing regulations, there is a promising potential for further fisheries research and to deepen the understanding of the life cycle to support the implementation of sound aquacultural practices to replenish exploited stocks and to develop commercial aquaculture. Currently, C. undecimalis populations in Mexico and the United States are overexploited, focusing on México, which now has a management plan. Advances in controlled reproduction and larval development have been made. However, many challenges remain unclear, such as larval conditions that continue to represent a bottleneck to block continuous and large‐scale aquaculture production, larval nutrition, disease management and culture systems. However, aquaculture holds the potential to enhance the sustainability of this species by reducing fishing pressure and aiding population recovery.

Chemical Composition, Bioactivities, and Applications of Spirulina (Limnospira platensis) in Food, Feed, and Medicine.

Spirulina (Limnospira platensis) is a microalga recognised for its rich nutritional composition and diverse bioactive compounds, making it a valuable functional food, feed, and therapeutic agent. This review examines spirulina's chemical composition, including its high levels of protein, essential fatty acids, vitamins, minerals, and bioactive compounds, such as the phycocyanin pigment, polysaccharides, and carotenoids, in food, feed, and medicine. These compounds exhibit various biological activities, including antioxidant, anti-inflammatory, immunomodulatory, antiviral, anticancer, antidiabetic and lipid-lowering effects. Spirulina's potential to mitigate oxidative stress, enhance immune function, and inhibit tumour growth positions it as a promising candidate for preventing chronic diseases. Additionally, spirulina is gaining interest in the animal feed sector as a promotor of growth performance, improving immune responses and increasing resistance to diseases in livestock, poultry, and aquaculture. Despite its well-documented health benefits, future research is needed to optimize production/cultivation methods, improve its bioavailability, and validate its efficacy (dose-effect relationship) and safety through clinical trials and large-scale human trials. This review underscores the potential of spirulina to address global health and nutrition challenges, supporting its continued application in food, feed, and medicine.

Antimicrobial Resistance in Lactococcus spp. Isolated from Native Brazilian Fish Species: A Growing Challenge for Aquaculture.

Lactococcus spp. has emerged as a pathogen that is affecting global aquaculture, with L. garvieae, L. petauri, and L. formosensis causing piscine lactococcosis. While antimicrobials are commonly used to treat diseases in aquaculture, reports of antimicrobial resistance in fish isolates are increasing. However, little is known about the susceptibility patterns of Lactococcus spp. strains isolated from native fish species in Brazil. This study aimed to assess the antimicrobial susceptibility of these strains and establish a provisional epidemiological cutoff value for L. garvieae using the normalized resistance interpretation approach. A total of 47 isolates were tested: 17 L. garvieae, 24 L. petauri, and 6 L. formosensis. The isolates were classified as wild-type (WT) or non-wild-type (NWT) based on inhibition zone diameters. Isolates classified as NWT for three or more antimicrobial classes were considered multidrug-resistant, and the multiple antibiotic resistance (MAR) index was calculated. The results revealed heterogeneity in antimicrobial resistance profiles, with higher resistance to trimethoprim/sulfamethoxazole and norfloxacin. Resistance to other antimicrobials, including florfenicol and oxytetracycline (approved for use in Brazil), varied according to the bacterial species. Lactococcus petauri (87.5%) and L. formosensis (66.7%) showed the highest multidrug resistance, compared to L. garvieae (11.7%), along with higher MAR index values. These findings suggest that multidrug-resistant strains could pose future challenges in the production of native species, underscoring the need for ongoing monitoring of antimicrobial resistance and responsible use of antimicrobials in aquaculture.

Shrimp Intestinal Microbiota Homeostasis: Dynamic Interplay Between the Microbiota and Host Immunity

ABSTRACTThe shrimp intestine harbors a microbiota that has pivotal roles for host's physiology. Imbalance of shrimp intestinal microbiota has been shown closely related to the occurrence of diseases. The morphological and biological features of the shrimp intestine are considered suboptimal for stable microbial colonization, making the intestinal microbiota composition highly susceptible to the impact of environmental changes or stressors, and particularly unstable. Therefore, the relative unsteadiness of the microbiota composition represents a continuous threat to host survival. Shrimp intestinal microbiota homeostasis is achieved through a dynamic interplay between the microbiota and the host's innate immunity. The shrimp intestine possesses effective innate immune mechanisms that can suppress the uncontrolled proliferation of microbiota components, and simultaneously protect the microbiota from elimination. The mechanism(s) by which the microbial components and the intestinal innate immunity interact with each other to achieve homeostasis represents an interesting interplay between host and microbiota. This review summarizes the current knowledge about intestinal microbiota colonization in shrimp, as well as the intricate mechanisms employed by the intestinal immune system to regulate this microbiota. Moreover, the potential intervention strategies to promote and protect shrimp intestinal homeostasis by modulating the microbiota are also discussed. Thus, this review seeks to comprehensively analyze the current information and contribute to a deeper understanding of the complex interplay between the shrimp intestinal microbiota and innate immunity in maintaining shrimp intestinal homeostasis and overall health. This enhanced understanding may potentially open new avenues for aquaculture management and disease mitigation strategies, ultimately benefiting the shrimp farming industry.

Evaluation of a Low-Temperature Immersion Immunization Strategy for the Infectious Spleen and Kidney Necrosis Virus orf037l Gene-Deleted Attenuated Vaccine

Background: Infectious spleen and kidney necrosis virus (ISKNV) poses a significant threat to aquaculture sustainability, particularly affecting mandarin fish (Siniperca chuatsi) and causing significant economic losses. Methods: To address this challenge, this study developed an ISKNV Δorf037l vaccine strain, where the orf037l gene was knocked out. Infection assays conducted at 28 °C showed that the knocking out the orf037l gene decreased the virulence of ISKNV and reduced lethality against mandarin fish by 26.7% compared to wild-type ISKNV. To further diminish residual virulence, the effect of low-temperature (22 °C) immersion immunization was evaluated. Results: The results indicate that low temperature significantly diminished the virulence of the Δorf037l vaccine strain, elevating the survival rate of mandarin fish to 90%. Furthermore, the vaccine strain effectively triggered the expression of crucial immune-related genes, such as IFN-h, IL-1, IκB, Mx, TNF-α, and Viperin, while inducing the production of specific neutralizing antibodies. Low-temperature immersion with Δorf037l achieved a high relative percentage of survival of 92.6% (n = 30) in mandarin fish, suggesting the potential of Δorf037l as a promising immersion vaccine candidate. Conclusions: These findings contribute to advancing fish immersion vaccine development and demonstrate the importance and broad applicability of temperature optimization strategies in vaccine development. Our work carries profound implications for both the theoretical understanding and practical application in aquaculture disease control.

Green synthesis and evaluation of dual herb-extracted DHM-AgNPs: Antimicrobial efficacy and low ecotoxicity in agricultural and aquatic systems

Uncontrolled applications of weedicide and fertilizer can harm the soil ecology, and most significantly, earthworms are hazardous soil engineers. Thus, we aimed at the toxicity and histopathological alterations in the earthworm Eudrilus euginae following exposure to glyphosate (weedicide), urea (fertilizer), and environmentally friendly dual herb-mixed silver nanoparticles (DHM-AgNPs). The DHM-AgNPs were synthesized using a blend of Alfinia officinarum and Curcuma longa aqueous leaf extracts with 1 mM silver nitrate. The color change from yellow to brown after an hour of incubation was a significant indicator of successful DHM-AgNP synthesis. Characterization of the DHM-AgNPs using UV–Vis spectra indicated a surface plasmon resonance (SPR) peak at 430 nm. In addition to FT-IR spectroscopy and XRD analysis, SEM, TEM, and SEM investigations were performed to identify the DHM-AgNPs. The XPS analysis revealed the oxidation state and surface chemical composition, and Ag NP's specific surface area and degree of porosity were measured using BET. Furthermore, different concentrations of urea and glyphosate were administered to Artemia nauplii and E. euginae to assess their toxicity. The mortality rate for E. euginae exposed to a higher urea concentration (10 g/kg of soil) was 100%. In contrast, a % mortality rate of 83% was noted at 0.5 g/kg of soil. The maximum mortality (90 ± 0.64%) was observed at a 10 mL/kg/L concentration for glyphosate. In contrast, low mortality was noted in E. euginae and A. nauplii exposed with gradient concentrations of DHM-AgNPs compared to glyphosate and urea. As aquaculture and foodborne diseases are widespread, DHM-AgNPs showed significant anti-Vibrio activity against pathogenic Vibrio-related bacteria, inhibiting 80% at 100,100 μg/L, which is of great concern. This study suggests the potential use of DHM-AgNPs in field aqua and crops culture for eco-friendly pest control and anti-Vibrio activity without causing soil and environmental pollution. Further research is warranted to determine the efficacy, safety, and cost-effectiveness of DHM-AgNPs in aqua and agricultural practices.

Akt inhibitors prevent CyHV-2 infection in vitro

Cyprinid herpesvirus 2 (CyHV-2) is a double-stranded DNA virus that infects goldfish (Carassius auratus) and crucian carp (C. carassius), resulting in substantial mortality rates and significant epidemiological implications. To gain deeper insights into CyHV-2-host interactions and identify potential therapeutic targets, quantitative proteomics analysis was conducted on CyHV-2-infected Ryukin goldfish fin (RyuF-2) cells. Our findings revealed significant alterations in the expression of proteins associated with the PI3K/Akt signaling pathway, which were up-regulated upon viral infection. Building on these observations, we employed LY294002, a specific inhibitor of PI3K, to investigate its impact on viral replication by inhibiting the PI3K/Akt pathway in GiCF cell line derived from the caudal fin of Carassius auratus gibelio (Bloch). Our results demonstrated the inhibition of both CyHV-2 replication and Akt phosphorylation within this pathway. Quercetin, a plant-derived analogue of LY294002, was further investigated for its anti-CyHV-2 effects in vitro as well as its underlying mechanism. The results suggested that quercetin exhibits antiviral properties against CyHV-2 and may exert its effects through mechanisms similar to those observed with LY294002. Given that aquaculture water serves as a vector for aquaculture viral diseases and the release of chemical compounds can lead to pollution of the aquatic environment, our study shifted focus to crude extracts obtained from plants. We confirmed crude quercetin extract derived from Cuminum anisum has antiviral activity against CyHV-2 in vitro. Therefore, based on our identification of the involvement of PI3K/Akt signaling pathway in CyHV-2 replication, along with verification of its antiviral mechanism using LY294002, we propose natural dietary quercetin as a promising candidate for development into a novel anti-CyHV-2 drug.

The potential role of galectin-4 in protecting the intestinal barrier in the lined seahorse Hippocampus erectus

Galectin-4 is a prominent antimicrobial peptide primarily expressed in the gastrointestinal tract of animals. It plays crucial roles in antimicrobial defense and in regulating the repair of intestinal epithelial cells. Given the unique immune system in seahorses, which are known for male pregnancy, the function of galectin-4 in their intestinal tract, which lack gut-associated lymphoid tissues, remains unknown. In this study, we identified a galectin-4 gene (HeGal-4) in the lined seahorse (Hippocampus erectus). The sequence length of the open reading frame (ORF) was 1041 bp, encoding 346 amino acids. The mRNA expression of HeGal-4 in the intestine was significantly higher than that in other internal organs. However, the synthesized peptide fragment (HeGal-4(302–315)) from the functional domain of HeGal-4 only showed moderate inhibitory effects against Escherichia coli, Klebsiella pneumoniae, and Micrococcus luteus. Interestingly, in situ hybridization showed that HeGal-4 was predominantly expressed in seahorse intestinal epithelial cells, while genes associated with galectin-4 in the repair of intestinal epithelium, such as β-catenins, were highly expressed in their intestines. Therefore, our results suggest that HeGal-4 may be crucial for regulating the repair of intestinal epithelial cells in seahorse intestinal epithelial cells, and that it possesses significant potential for the prevention and control of intestinal diseases in seahorse aquaculture.

In vitro efficacy of aquaculture antimicrobials and genetic determinants of resistance in bacterial isolates from tropical aquaculture disease outbreaks.

Understanding the efficacy of antimicrobials against pathogens from clinical samples is critical for their responsible use. The manuscript presents in vitro efficacy and antimicrobial resistance (AMR) genes in seven species of fish pathogens from the disease outbreaks of Indian aquaculture against oxytetracycline, florfenicol, oxolinic acid, and enrofloxacin. In vitro efficacy was evaluated by minimum inhibitory concentration and minimum bactericidal concentration. The gene-specific PCR screened AMR genes against quinolones (qnrA, qnrB, and qnrS) and tetracyclines (tetM, tetS, tetA, tetC, tetB, tetD, tetE, tetH, tetJ, tetG, and tetY). The results showed that Aeromonas veronii (45%) showed the maximum resistance phenotype, followed by Streptococcus agalactiae (40%), Photobacterium damselae (15%), Vibrio parahaemolyticus (10%), and Vibrio vulnificus (5%). There was no resistance among Vibrio harveyi and Vibrio alginolyticus against the tested antimicrobials. The positive association between tetA, tetB, tetC, tetM, or a combination of these genes to oxytetracycline resistance and qnrS to quinolone resistance indicated their potential in surveillance studies. The prevalence of resistance phenotypes (16.43%) and evaluated AMR genes (2.65%) against aquaculture antimicrobials was low. The resistance phenotype pattern abundance was 0.143. All the isolates showed susceptibility to florfenicol. The results help with the appropriate drug selection against each species in aquaculture practices.

Positively charged mesoporous silica nanocarriers loaded with arbidol: A novel effective nano antiviral system against nervous necrosis virus

Viral nervous necrosis (VNN) caused by nervous necrosis virus (NNV) poses a significant threat to the global aquaculture industry, leading to substantial economic losses. In this study, we evaluated the anti-NNV activity of arbidol both in vitro and in vivo. Treatment with arbidol at a concentration of 10.48 μM effectively inhibited NNV-induced cytopathic effects in GF-1 cells, and the half-maximal inhibitory concentration (IC50) of arbidol against NNV was determined to be 7.915 μM. To improve drug delivery to the central nervous system, the primary site of NNV infection, we developed positively charged mesoporous silica nanocarriers (CMSNs) loaded with arbidol (CMSNs-ARB). Compared to unmodified mesoporous silica nanocarriers, CMSNs exhibited significantly higher uptake in GF-1 cells and zebrafish brains, indicating their potential to cross the blood-brain barrier (BBB) and deliver drugs more efficiently. In vivo experiments revealed that arbidol administration improved the survival rate of juvenile fish infected with NNV. Additionally, the use of CMSNs as a drug carrier further enhanced the larval survival rate by 13 % compared to the arbidol-only treatment group. These results demonstrate the potent anti-NNV activity of arbidol and highlight the potential of CMSNs as an effective drug delivery system to control fish viral diseases in aquaculture.

Pharmacokinetics, optimal dosages and withdrawal time of amoxicillin in Nile tilapia (Oreochromis niloticus) reared at 25 and 30 °C

Knowledge of amoxicillin (AMX) pharmacokinetics (PK) and tissue residues in fish, which is necessary for prudent drug use, remains limited. The study aimed to explore the PK characteristics of AMX in Nile tilapia (Oreochromis niloticus) reared at 25 and 30 °C as well as to determine optimal dosages and drug withdrawal time (WDT). In the PK investigation, the fish received a single dose of 40 mg/kg AMX via oral gavage, and the optimal dosage was determined by the pharmacokinetic-pharmacodynamic approach. In the tissue residue study, the fish were orally gavaged with 40 mg/kg/day AMX once daily for 5 days and the WDT was established by the linear regression analysis. The results revealed the temperature-dependent drug elimination; the clearance relative to bioavailability (CL/F) and elimination half-life at 30 °C (0.180 L/kg/h and 6.06 h, respectively) were about twice those at 25 °C (0.090 L/kg/h and 10.49 h, respectively). The optimal dosages at the minimum inhibitory concentration (MIC) of 2 μg/mL were 10.97 (25 °C) and 41.03 (30 °C) mg/kg/day, respectively. Finally, following the multiple oral administration, the muscle/skin residue of AMX on day 1 after the last dosing at 25 and 30 °C were 548 and 264 ng/g, respectively. The average tissue residues were depleted below the maximum residue limits (MRL) of 50 μg/kg on day 5 (25 °C) and 3 (30 °C), respectively, and the WDT were 6 and 4 days when rearing at 25 and 30 °C, respectively. This knowledge serves as a practical guideline for responsible use of AMX in treating bacterial diseases in Nile tilapia aquaculture.

Metabolomic analysis revealed the inflammatory and oxidative stress regulation in response to Vibrio infection in Plectropomus leopardus.

Frequent outbreaks of infectious diseases in aquaculture have led to significant economic losses. The leopard coral grouper (Plectropomus leopardus) often suffers from vibriosis. Improving host immunity presents a superior strategy for disease control, with minimal side effects compared to the use of antibiotics, highlighting the necessity of exploring the mechanisms underlying the fish's response to pathogen infections. Here, we conducted a comparative metabolomic analysis on the livers of the P. leopardus infected with Vibrio harveyi. A total of 1124 differential metabolites (DMs) were identified, with 190, 218, 359, and 353 DMs being identified at 6, 12, 24, and 48 h post-infection (hpi), respectively. Then, based on the time series analysis, we found that the lipid metabolism pathways were modulated in response to the Vibrio infection, with an increase in the quantity of eicosanoids and gycerophospholipids (GPLs), as well as a decrease in the quantity of bile acids (BAs), vitamin D, and sex hormones. Furthermore, 13 enriched pathways involving 31 DMs were identified through KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment analyses. We identified histamine, 15(S)-HpETE, and anandamide in the transient receptor potential (TRP) channels pathway, as well as (7S,8S)-DiHODE, 5S,8R-DiHODE, and 13(S)-HpODE in the linoleic acid (LA) metabolism pathway. The DM levels increased, which may be attributed to inflammation. The DMs in the thyroid hormone synthesis pathway were identified, and the contents of nicotinamide adenine dinucleotide phosphate (NADPH) and glutathione (GSH) decreased, which may be crucial in antioxidants. Our findings highlighted the dynamic adjustments in lipid metabolism and the response to inflammation and oxidative stress during the infection of V. harveyi in P. leopardus. This study not only deepens our understanding of the metabolic underpinnings of fish immune responses but also lays the groundwork for research into functional metabolomics and mechanisms of disease resistance.

IgT-mediated mucosal immunity and microbiota dynamics in snakehead (Channa argus) post Aeromonas veronii TH0426 and Aeromonas hydrophila TPS infection: implications for aquaculture disease management.

The aquaculture sector, vital to global food security, grapples with bacterial pathogens compromising fish health and industry sustainability. This investigation probes mucosal immune responses and gut microbiota dynamics in snakehead (Channa argus) post-Aeromonas infection, a prevalent aquaculture challenge. Employing infection models, we delineated the integral role of immunoglobulin T (IgT) in mucosal immunity and its interaction with gut microbiota. Fish from a local farm, maintained under controlled conditions, were infected with Aeromonas veronii TH0426 and Aeromonas hydrophila TPS. Post-infection, daily monitoring and sample collection at specified intervals were conducted for comprehensive analysis. Histopathology, quantitative PCR, immunofluorescence, and microbiota profiling revealed significant immune and microbial changes, particularly at day 7. Intestinal IgT, IgM, and pIgR gene expression surged, indicative of a robust response. Immunofluorescence microscopy confirmed increased IgT+ and pIgR+ cell infiltration in the epithelium. Post-infection dysbiosis, with altered bacterial composition, was partially offset by elevated IgT levels. These insights underscore IgT's crucial function in mucosal defense and suggest potential for probiotic and vaccine strategies to enhance aquaculture disease resilience.

Genomic Sequence of Streptococcus salivarius MDI13 and Latilactobacillus sakei MEI5: Two Promising Probiotic Strains Isolated from European Hakes (Merluccius merluccius, L.).

Frequently, diseases in aquaculture have been fought indiscriminately with the use of antibiotics, which has led to the development and dissemination of (multiple) antibiotic resistances in bacteria. Consequently, it is necessary to look for alternative and complementary approaches to chemotheraphy that are safe for humans, animals, and the environment, such as the use of probiotics in fish farming. The objective of this work was the Whole-Genome Sequencing (WGS) and bioinformatic and functional analyses of S. salivarius MDI13 and L. sakei MEI5, two LAB strains isolated from the gut of commercial European hakes (M. merluccius, L.) caught in the Northeast Atlantic Ocean. The WGS and bioinformatic and functional analyses confirmed the lack of transferable antibiotic resistance genes, the lack of virulence and pathogenicity issues, and their potentially probiotic characteristics. Specifically, genes involved in adhesion and aggregation, vitamin biosynthesis, and amino acid metabolism were detected in both strains. In addition, genes related to lactic acid production, active metabolism, and/or adaptation to stress and adverse conditions in the host gastrointestinal tract were detected in L. sakei MEI5. Moreover, a gene cluster encoding three bacteriocins (SlvV, BlpK, and BlpE) was identified in the genome of S. salivarius MDI13. The in vitro-synthesized bacteriocin BlpK showed antimicrobial activity against the ichthyopathogens Lc. garvieae and S. parauberis. Altogether, our results suggest that S. salivarius MDI13 and L. sakei MEI5 have a strong potential as probiotics to prevent fish diseases in aquaculture as an appropriate alternative/complementary strategy to the use of antibiotics.

Effects of hydrogen peroxidase-inactivated vaccine against Streptococcus agalactiae infection in red tilapia (Oreochromis sp.) via different routes of administration

Hydrogen peroxidase-inactivated vaccines have recently developed in controlling infectious diseases in aquaculture. The present study aimed to compare the efficacy of the hydrogen peroxidase-inactivated Streptococcus agalactiae vaccine via different delivery routes (injection, immersion, and oral administration) in red tilapia (Oreochromis sp.) without using adjuvant. Fish were randomly divided into 4 groups including G1: Control treatment (without vaccine), G2: vaccine-based diet (oral administration), G3: vaccinated by immersion and G4: vaccinated by injection. After 6 weeks of the experiment, fish were intraperitoneally injected with S. agalactiae and the mortality was recorded in 14 days. The results showed that lysozyme activity was differentially increased according to the delivery routes of vaccine, organs and time of sampling. However, the specific antibody levels in all vaccinated groups were only increased in week 6 post-vaccination. After the challenge test with S. agalactiae, the serum lysozyme levels in G3 and G4 were significantly higher than the control group (G1), while the total white blood cells and specific antibody levels were significantly increased in G2 and G4 compared to the control (G1). Similarly, the hydrogen peroxidase-inactivated vaccine statistically reduced the cumulative mortality in G2 (35.29%) and G4 (28.95%) compared to G1 (44.12%) after injected with the S. agalactiae. These results showed that the vaccine delivery routes by oral administration or injection may decrease the pathogen and show better protection for red tilapia than the immersion method. Further studies will be investigated to improve the efficacy of hydrogen peroxidaseinactivated vaccine via using different adjuvants.

Bacterial recognition and inhibition activities of an LRR-only protein in the Chinese mitten crab, Eriocheir sinensis

LRR-only protein (LRRop) is an important class of immune molecules that function as pattern recognition receptor in invertebrates, however, the bacterial inhibitory activity of this proteins remain largely unknown. Herein, a novel LRRop was cloned from Eriocheir sinensis and named as EsLRRop2. The EsLRRop2 consists of six LRR motifs and formed a horseshoe shape three-dimension structure. EsLRRop2 was mainly expressed in intestine and hepatopancreas. The transcripts of EsLRRop2 in the intestine and hepatopancreas were induced by Vibrio parahaemolyticus and Staphylococcus aureus, and displayed similar transcriptional profiles. The expression levels of EsLRRop2 responded more rapidly and highly to V. parahaemolyticus than S. aureus in the intestine and hepatopancreas. Although the basal expression level of EsLRRop2 in hemocytes was relatively low, its transcripts in hemocytes were significantly induced by V. parahaemolyticus and S. aureus. The recombinant proteins of EsLRRop2 (rEsLRRop2) displayed a wide range of binding spectrum against vibrios, including V. parahaemolyticus, V. alginolyticus, and V. harveryi. The rEsLRRop2 showed dose- and time-dependent inhibitory activity against V. parahaemolyticus and S. aureus, and it could agglutinate the two bacteria. Furthermore, the inhibitory activities of rEsLRRop2 against V. parahaemolyticus, V. alginolyticus, V. harveryi and S. aureus was slightly affected by pH and salinity, and the rEsLRRop2 displayed the strongest inhibitory activity against all the three vibrios when the salinity was 20 ‰ and pH was 8.0. Collectively, these results elucidate the bacterial binding and inhibitory activities of EsLRRop2, and provide theoretical foundations for the application of rEsLRRop2 in prevention and control of vibrio diseases in aquaculture.

A checklist of the monogenean parasites (Platyhelminthes) of fishes of northeast India.

A checklist was generated by compiling a database of all available published accounts of the monogenean parasites of fish from northeast India. The checklist is presented as a host-parasite list, including 35 nominal species from 14 genera and 3 families of monogeneans. Ten of the monogenean species listed here have been described from native fishes in the region, while 25 had previously been described from other parts of India. Dactylogyridae was the dominant family with 33 species, followed by one species each from the family Sundanonchidae and Diplozoidae. Wallago attu was the most examined fish and was represented by five parasite species. This study is an important step for managing and controlling parasite diseases in regional aquaculture and also for future research on the ecology, evolutionary biology, and biogeography of monogenean parasites and their hosts. More significant efforts are needed to fully understand the diversity of monogenean parasites from the rich fish fauna of northeast India.

Bacillus coagulans restores pathogen-induced intestinal dysfunction via acetate-FFAR2-NF-κB-MLCK-MLC axis in Apostichopus japonicus.

Skin ulceration syndrome (SUS) is currently the main disease threatening Apostichopus japonicus aquaculture due to its higher mortality rate and infectivity, which is caused by Vibrio splendidus. Our previous studies have demonstrated that SUS is accompanied by intestinal microbiota (IM) dysbiosis, alteration of short-chain fatty acids (SCFAs) content and the damage to the intestinal barrier. However, the mediating effect of IM on intestine dysfunction is largely unknown. Herein, we conducted comprehensive intestinal microbiota transplantation (IMT) to explore the link between IM and SUS development. Furthermore, we isolated and identified a Bacillus coagulans strain with an ability to produce acetic acid from both healthy individual and SUS individual with IM from healthy donors. We found that dysbiotic IM and intestinal barrier function in SUS recipients A. japonicus could be restored by IM from healthy donors. The B. coagulans strain could restore IM community and intestinal barrier function. Consistently, acetate supply also restores intestinal homeostasis of SUS-diseased and V. splendidus-infected A. japonicus. Mechanically, acetate was found to specifically bind to its receptor-free fatty acid receptor 2 (FFAR2) to mediate IM structure community and intestinal barrier function. Knockdown of FFAR2 by transfection of specific FFAR2 siRNA could hamper acetate-mediated intestinal homeostasis in vivo. Furthermore, we confirmed that acetate/FFAR2 could inhibit V. splendidus-activated NF-κB-MLCK-MLC signaling pathway to restore intestinal epithelium integrity and upregulated the expression of ZO-1 and Occludin. Our findings provide the first evidence that B. coagulans restores pathogen-induced intestinal barrier dysfunction via acetate/FFAR2-NF-κB-MLCK-MLC axis, which provides new insights into the control and prevention of SUS outbreak from an ecological perspective.IMPORTANCESkin ulceration syndrome (SUS) as a main disease in Apostichopus japonicus aquaculture has severely restricted the developmental A. japonicus aquaculture industry. Intestinal microbiota (IM) has been studied extensively due to its immunomodulatory properties. Short-chain fatty acids (SCFAs) as an essential signal molecule for microbial regulation of host health also have attracted wide attention. Therefore, it is beneficial to explore the link between IM and SUS for prevention and control of SUS. In the study, the contribution of IM to SUS development has been examined. Additionally, our research further validated the restoration of SCFAs on intestinal barrier dysfunction caused by SUS via isolating SCFAs-producing bacteria. Notably, this restoration might be achieved by inhibition of NF-κB-MLCK-MLC signal pathway, which could be activated by V. splendidus. These findings may have important implications for exploration of the role of IM in SUS occurrence and provide insight into the SUS treatment.