Immune Response In Fish Research Articles

Effects of insect meals on fish digestibility, blood parameters, and economic performance: a meta-analysis

Abstract This review examines the use of insect meal (IM) as a substitute for fishmeal (FM) in fish feeds within the past decade. While global interest in this alternative is growing, research on its effects on fish digestibility, blood parameters, and economic performance has been limited. Meta-analysis on the apparent digestibility coefficient revealed a negative effect summary on dry matter (−0.92) and crude lipid (−0.51), although the difference between the two groups was relatively minor. However, a positive effect summary was reported in the apparent digestibility of crude protein (0.12), suggesting a potential advantage in the utilization of protein by fish fed with IM-containing diets. Whereas meta-analysis on fish blood parameters demonstrates varying effects summary, necessitating further research. Analysis of economic performance revealed an overall better economic performance in the IM diet with an effect summary of −0.08 for feed cost and 0.00 for the economic profit index. Overall use of IM in aquafeed shows promise in improving feed quality and fish performance, potentially becoming a sustainable alternative to traditional FM. Recommendations include exploring IM’s impact on fish blood parameters through more investigations. Shifting focus from traditional measures to markers directly linked with fish health and immune response can provide more precise insights. Moreover, exploring various components of IM, such as lipids and functional elements like chitin, through simplified breakdown methods, can significantly enhance our comprehension of their nutritional value. Analyzing how each part influences fish health could pave the way for a sustainable and efficient alternative to FM in aquaculture.

Pesticides and Heavy Metal Toxicity in Fish and Possible Remediation – A Review

Abstract Pesticides and heavy metals are considered as potent contaminants in aquatic environment. Both contaminants are sourced into the aquatic ecosystems by various types of anthropogenic as well as natural practices. Such types of aquatic contamination drastically affect the normal activity of associated living organisms particularly fish. Both the pesticides and heavy metals toxicity cause several negative effects on fish growth, physiology, immune response, reproduction, embryonic and larval development as well as different histopathology of major organs including fish gill, kidney, liver, gonads, and intestine. Besides, the consumption of contaminated fish poses a serious health concern to associated consumers. Considering these serious issues, the current review is designed to investigate the toxic effects of pesticides and heavy metals on different aspects of fishes along with their possible sources, major types, and mode of action as well as role of medicinal herbs to mitigate their toxicity.

Genome-wide identification of DNA methylation marks associated with resistance to Streptococcus agalactiae in the GIFT strain of Nile Tilapia (Oreochromis niloticus)

Epigenetic mechanism plays a pivotal role in the immune responses of fish. Streptococcus agalactiae (SA) infection is a significant challenge to tilapia aquaculture. DNA methylation involved in immune responses in tilapia against SA is unclear. Here, by using a QTLseq strategy integrated with whole-genome bisulfite sequencing-based DNA methylation analysis (methyl-QTLseq) and RNA sequencing (RNA-seq), we identified 3608 differentially methylated regions (DMRs) and 4355 differentially expressed genes (DEGs) in the spleen of Nile tilapia Oreochromis niloticus. Compared to the susceptible group, the up-regulated DMRs (2449) were approximately twice as many as the down-regulated DMRs (1159). Compared to the susceptible group, lower methylation levels for CpG, CHG and CHH in TEs and for CHG and CHH in genes and significant decreased expression for 8 of the 11 DNA methyltransferase genes in the resistant group were detected. 46 DEGs with differentially methylated promoter regions (DMPs) were significantly enriched in immune processes such as T cell differentiation and adaptive immunity. We detected 4 methyl-QTLs located on LG8:5332501–5,336,400, LG14:2307301–2,353,500, LG16:16889101–16,903,500, and LG22:25238401–2,536,880 across the tilapia genome. The methyl-QTL region located within the chromosome LG22:25238401–25,368,800 contains the most DMRs (91) and DMGs (7). Interestingly, most of the annotated genes that located within or under the peak of the methyl-QTL interval belong to the HOX protein family including hoxa1, hoxa2, hoxa4a and hoxa5a. Bisulfite sequencing PCR and expression analysis indicated that DNA methylation in the promoter regions of hoxa4a, lcp2a, and ccr9a regulated gene expression in spleen in response to SA infection. Overall, our study provides epigenetics evidences involving in immune responses against SA infection in tilapia.

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.

Comprehensive profiling of lncRNAs in the immune response of largemouth bass to Nocardia Seriolae infection

Long noncoding RNAs (lncRNAs) are crucial regulators of various biological processes. However, it remains unclear how lncRNAs can be involved in the immune response to Nocardia seriolae invasion in largemouth bass (Micropterus salmoides). Here we leveraged the whole transcriptome RNA-seq technique to screen lncRNAs associated with the head kidney infected with Nocardia seriolae. A total of 5,661 lncRNAs were identified, comprising 2,427 known lncRNAs and 3,234 novel lncRNAs. Among these, 531 lncRNAs were found to be differentially expressed, with 213 showing increased expression and 318 showing reduced expression. In these differentially expressed lncRNAs, 176 lncRNAs may have cis-regulatory relationships with 243 protein-coding genes. For example, MSTRG.17818.1, MSTRG.10160.1 target mapk1 and rela, respectively, thereby regulating gene expression. We then exploited Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) to analyze the enrichment of target genes of lncRNAs. These target genes were found to be significantly enriched in immune signaling pathways, including RIG-I-like receptor signaling and Toll-like receptor signaling. Furthermore, we harnessed a total of 12 mRNAs, 33 miRNAs, and 167 lncRNAs to construct two lncRNA-miRNA-mRNA network maps. CeRNA maps revealed that some lncRNAs can competitively bind to the same miRNA and affect the expression of immune-related genes. For instance, MSTRG.13668.1 and MSTRG.5180.1 can simultaneously bind to mir-155–5p to increase irak4 expression. These findings suggest that lncRNAs may participate in the immune response process of infected largemouth bass with Nocardia seriolae. Overall, this work presents a thorough lncRNAs expression profile of Nocardia seriolae-infected largemouth bass and offers insights into the ceRNA regulatory processes that influence fish's immune response to bacterial infections.

Application of nervous necrosis virus capsid protein-based antigen-presenting particles for vaccine development

Nervous necrosis virus (NNV) capsid protein plays an important role in producing viral particles without any genetic elements. Thus, NNV is a promising candidate for vaccine development and is widely used for constructing vaccines, including DNA, recombinant proteins, and virus-like particles (VLPs). Our study aimed to investigate the potential of NNV capsid protein (NNV) and NNV capsid protein fused to enhanced green fluorescent protein (NNV-EGFP) through VLP formation and whether their application can induce specific antibody responses against certain antigens. We focused on producing DNA and recombinant protein vaccines consisting of the genes for NNV, EGFP, and NNV-EGFP. The approach using NNV-EGFP allowed NNV to act as a carrier or inducer while EGFP was incorporated as part of the capsid protein, thereby enhancing the immune response. In vitro studies demonstrated that all DNA vaccines expressed in HINAE cells resulted in varying protein expression levels, with particularly low levels observed for pNNV and pNNV-EGFP. Consequently, structural proteins derived from HINAE cells could not be observed using transmission electron microscopy (TEM). In contrast, recombinant proteins of NNV and NNV-EGFP were expressed through the Escherichia coli expression system. TEM revealed that rNNV was assembled into VLPs with an approximate size of 30 nm, whereas rNNV-EGFP presented particles ranging from 10 nm to 50 nm in size. For the vaccination test, DNA vaccination marginally induced specific antibody responses in Japanese flounder compared to unvaccinated fish. Meanwhile, NNV and NNV-EGFP recombinant vaccines enhanced a greater anti-NNV antibody response than the others, whereas antibody responses against EGFP were also marginal. These results indicate that NNV capsid protein-based antigens, presenting as particles, play an important role in eliciting a specific anti-NNV antibody response and have the potential to improve fish immune responses.

A meta‐analysis of the effects of black soldier fly meal on fish immune response and antioxidant capacity

Black soldier fly (BSF) meal possesses a balanced nutritional profile, making it a promising substitute for fishmeal. Several studies have been conducted to investigate the effects of replacing fishmeal with BSF meal on fish immune response and antioxidant capacity. However, considering the varying effects of BSF meal on different fish species demonstrated in earlier studies, a meta-analysis study was imperative to determine the efficacy of BSF meal in aquafeed. This meta-analysis examined 38 studies on finfish. Subgroup analysis and meta-regression were conducted to investigate the source of heterogeneity in the immunostimulant and antioxidant efficacy of BSF meal. Categorical variables used in subgroup analysis included the BSF development stage (larvae versus prepupae or pupae), BSF processing method (full-fat versus defatted), and fish dietary habits. Two continuous variables were evaluated for meta-regression analysis: dietary BSF inclusion level and treatment duration. The datasets were assessed for publication bias using funnel plots and Egger's test with the Pustejovsky–Rodgers Approach. The results revealed that BSF meal influences immune performance and antioxidant ability. Subgroup analysis indicated that different BSF development stages significantly influence the immunostimulant and antioxidant efficacy of BSF meals, with BSF prepupae or pupae outperforming BSF larvae. In terms of processing, full-fat BSF was superior to defatted BSF. Furthermore, BSF meal demonstrated the highest efficacy in omnivorous fishes. Meta-regression outcomes revealed that a higher concentration of BSF meal may inhibit immune response and antioxidant ability and that treatment duration exerts little impact. In conclusion, the present meta-analysis demonstrated that BSF is a promising ingredient in aquafeed to improve fish immune response and antioxidant capacity.

Insights into the connection between pathogen water eDNA and disease progression in zebrafish infected with Vibrio anguillarum

The host-pathogen interactions are tripartite and include the host, the pathogen, and the environment. For a long time, attention has mainly been addressed to the host's immune mechanisms and the pathogen's virulence factors while the environmental factor has received less interest. About a decade ago, studies on environmental DNA (eDNA) started to emerge as this approach is versatile for numerous research fields and interest is persistently growing. In the present study, the relationship between disease progression and pathogen water environmental DNA level was investigated. To perform this investigation, an infection model was setup using zebrafish and the gram-negative bacteria Vibrio anguillarum. Two different fish densities and bacterial concentrations were used to determine different patterns of pathogen eDNA in the fish tanks. Water sampling to collect eDNA was conducted alongside with observation of the fish Clinical Signs, mortalities, and immune responses. Water eDNA relative abundance of the pathogen could be determined directly after fish challenge, when Clinical Signs occurred, and when mortality started. Moreover, immune-relevant gene expression in zebrafish gills showed that il-1β, il-8, il-10, nf-κb and saa correlated to the pathogen eDNA signal, depending on fish density and bacterial concentration. In conclusion, this study demonstrated that water eDNA is a promising non-invasive tool to state disease progression and immune response in zebrafish infected with V. anguillarum.

Effects of Flour Extract of Leaves of Terminalia catappa (L) on Aeromonas Motile Septicemia in Cyprinus carpio (L) Larvae

This study aimed to evaluate the effectiveness of Terminalia catappa (L) leaf flour extract in controlling Motile Aeromonas Septicemia (MAS) disease caused by A. hydrophila in common carp larvae. The research method used in this study is an experimental method using a complete randomized design (RAL). This research consists of 2 stages; in vitro and in vivo tests using T. catappa leaf extract. In vitro test, T. catappa leaf extract consists of 5 different doses; The treatments consisted of 0 (negative control), 20, 40, 80, and 100 g L-1 T. catappa leaf flour extract and Stroptomycinsulphate 0.005 g (positive control). In vivo test, 3 best doses were selected based on the diameter zone of inhibition; 60, 80, and 100 g L-1, with positive (using Stroptomycinsulphate 0.005 g and untreated sample (without T. catappa leaf flour extract), each with 3 replicates. The results showed that using T. catappa leaf flour extract can significantly increase the fish's immune response, resistance, and survival. Duncan's further test showed that the 100 g L-1 dose treatment revealed an increase in immune response and survival rate compared to the F and G treatments.

Nervous necrosis virus capsid protein and Protein A dynamically modulate the fish cGAS-mediated IFN signal pathway to facilitate viral evasion.

Nervous necrosis virus (NNV), an aquatic RNA virus belonging to Betanodavirus, infects a variety of marine and freshwater fishes, leading to massive mortality of cultured larvae and juveniles and substantial economic losses. The enzyme cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) is widely recognized as a central component in the innate immune response to cytosolic DNA derived from different pathogens. However, little is known about the response of cGAS to aquatic RNA viruses. This study found that Epinephelus coioides cGAS (EccGAS) overexpression inhibited NNV replication, whereas EccGAS silencing promoted NNV replication. The anti-NNV activity of EccGAS was involved in interferon (IFN) signaling activation including tumor necrosis factor receptor-associated factor family member-associated NF-kappa-B activator-binding kinase 1 (TBK1) phosphorylation, interferon regulatory factor 3 (IRF3) nuclear translocation, and the subsequent induction of IFNc and ISGs. Interestingly, NNV employed its capsid protein (CP) or Protein A (ProA) to negatively or positively modulate EccGAS-mediated IFN signaling by simultaneously targeting EccGAS. CP interacted with EccGAS via the arm-P, S-P, and SD structural domains and promoted its polyubiquitination with K48 and K63 linkages in an EcUBE3C (the ubiquitin ligase)-dependent manner, ultimately leading to EccGAS degradation. Conversely, ProA bound to EccGAS and inhibited its ubiquitination and degradation. In regulating EccGAS protein content, CP's inhibitory action was more pronounced than ProA's protective effect, allowing successful NNV replication. These novel findings suggest that NNV CP and ProA dynamically modulate the EccGAS-mediated IFN signaling pathway to facilitate the immune escape of NNV. Our findings shed light on a novel mechanism of virus-host interaction and provide a theoretical basis for the prevention and control of NNV.IMPORTANCEAs a well-known DNA sensor, cGAS is a pivotal component in innate anti-viral immunity to anti-DNA viruses. Although there is growing evidence regarding the function of cGAS in the resistance to RNA viruses, the mechanisms by which cGAS participates in RNA virus-induced immune responses in fish and how aquatic viruses evade cGAS-mediated immune surveillance remain elusive. Here, we investigated the detailed mechanism by which EccGAS positively regulates the anti-NNV response. Furthermore, NNV CP and ProA interacted with EccGAS, regulating its protein levels through ubiquitin-proteasome pathways, to dynamically modulate the EccGAS-mediated IFN signaling pathway and facilitate viral evasion. Notably, NNV CP was identified to promote the ubiquitination of EccGAS via ubiquitin ligase EcUBE3C. These findings unveil a novel strategy for aquatic RNA viruses to evade cGAS-mediated innate immunity, enhancing our understanding of virus-host interactions.

Environmental influence on the Atlantic salmon transcriptome and methylome during sea lice infestations

The fish's immune response is affected by different factors, including a wide range of environmental conditions that can also disrupt or promote changes in the host-pathogen interactions. How environmental conditions modulate the salmon genome during parasitism is poorly understood here. This study aimed to explore the environmental influence on the Salmo salar transcriptome and methylome infected with the sea louse Caligus rogercresseyi. Atlantic salmon were experimentally infected with lice at two temperatures (8 and 16 °C) and salinity conditions (32 and 26PSU). Fish tissues were collected from the infected Atlantic salmon for reduced representation bisulfite sequencing (RRBS) and whole transcriptome sequencing (RNA-seq) analysis. The parasitic load was highly divergent in the evaluated environmental conditions, where the lowest lice abundance was observed in fish infected at 8 °C/26PSU. Notably, transcriptome profile differences were statistically associated with the number of alternative splicing events in fish exposed to low temperature/salinity conditions. Furthermore, the temperature significantly affected the methylation level, where high values of differential methylation regions were observed at 16 °C. Also, the association between expression levels of spliced transcripts and their methylation levels was determined, revealing significant correlations with Ferroptosis and TLR KEEG pathways. This study supports the relevance of the environmental conditions during host-parasite interactions in marine ecosystems. The discovery of alternative splicing transcripts associated with DMRs is also discussed as a novel player in fish biology.

TLR21 is involved in the NF-κB and IFN-β pathways in largemouth bass (Micropterus salmoides) and interacts with TRIF but not with the Myd88 adaptor

Toll-like receptors (TLRs) are pattern recognition receptors that trigger host immune responses against various pathogens by detecting evolutionarily conserved pathogen-associated molecular patterns (PAMPs). TLR21 is a member of the Toll-like receptor family, and emerging data suggest that it recognises unmethylated CpG DNA and is considered a functional homologue of mammalian TLR9. However, little is known regarding the role of TLR21 in the fish immune response. In the present study, we isolated the cDNA sequence of TLR21 from the largemouth bass (Micropterus salmoides) and termed it MsTLR21. The MsTLR21 gene contained an open reading frame (ORF) of 2931 bp and encodes a polypeptide of 976 amino acids. The predicted MsTLR21 protein has two conserved domains, a conserved leucine-rich repeats (LRR) domain and a C-terminal Toll-interleukin (IL) receptor (TIR) domain, similar to those of other fish and mammals. In healthy largemouth bass, the TLR21 transcript was broadly expressed in all the examined tissues, with the highest expression levels in the gills. After challenge with Nocardia seriolae and polyinosinic polycytidylic acid (Poly[I:C]), the expression of TLR21 mRNA was upregulated or downregulated in all tissues tested. Overexpression of TLR21 in 293T cells showed that it has a positive regulatory effect on nuclear factor-kappaB (NF-κB) and interferons-β (IFN-β) activity. Subcellular localisation analysis showed that TLR21 was expressed in the cytoplasm. We performed pull-down assays and determined that TLR21 did not interact with myeloid differentiation primary response gene 88 (Myd88); however, it interacted with TIR domain-containing adaptor inducing interferon-β (TRIF). Taken together, these findings suggest that MsTLR21 plays important roles in TLR/IL-1R signalling pathways and the immune response to pathogen invasion.

Role of Medaka (Oryzias latipes) Foxo3 in Resistance to Nervous Necrosis Virus Infection.

Upon encountering a virus, fish initiate an innate immune response, guided by IFNs. Foxo3 plays a part in the body's immune response; however, its specific role in the IFN-guided immune response in fish is yet to be clarified. In this study, we characterized foxo3 in Japanese medaka (Oryzias latipes) and examined its role in the IFN-dependent immune response upon infection with the RGNNV. The results show that the coding region of the medaka foxo3 gene is 2007 base pairs long, encoding 668 amino acids, and possesses a typical forkhead protein family structural domain. The product of this gene shares high homology with foxo3 in other fish species and is widely expressed, especially in the brain, eyes, testes, and heart. Upon RGNNV infection, foxo3-/- mutant larvae showed a lower mortality rate, and adults exhibited a significant reduction in virus replication. Moreover, the absence of foxo3 expression led to an increase in the expression of irf3, and a decrease in the expression of other IFN-related genes such as tbk1 and mapk9, implying that foxo3 may function as a negative regulator in the antiviral signaling pathway. These findings provide crucial insights for disease-resistant breeding in the aquaculture industry.

Vegetable omega-3 and omega-6 fatty acids differentially modulate the antiviral and antibacterial immune responses of Atlantic salmon

The immunomodulatory effects of omega-3 and omega-6 fatty acids are a crucial subject of investigation for sustainable fish aquaculture, as fish oil is increasingly replaced by terrestrial vegetable oils in aquafeeds. Unlike previous research focusing on fish oil replacement with vegetable alternatives, our study explored how the omega-6 to omega-3 polyunsaturated fatty acid (PUFA) ratio in low-fish oil aquafeeds influences Atlantic salmon's antiviral and antibacterial immune responses. Atlantic salmon were fed aquafeeds rich in soy oil (high in omega-6) or linseed oil (high in omega-3) for 12 weeks and then challenged with bacterial (formalin-killed Aeromonas salmonicida) or viral-like (polyriboinosinic polyribocytidylic acid) antigens. The head kidneys of salmon fed high dietary omega-3 levels exhibited a more anti-inflammatory fatty acid profile and a restrained induction of pro-inflammatory and neutrophil-related genes during the immune challenges. The high-omega-3 diet also promoted a higher expression of genes associated with the interferon-mediated signaling pathway, potentially enhancing antiviral immunity. This research highlights the capacity of vegetable oils with different omega-6 to omega-3 PUFA ratios to modulate specific components of fish immune responses, offering insights for future research on the intricate lipid nutrition-immunity interplay and the development of novel sustainable low-fish oil clinical aquaculture feeds.

Use of Bacillus subtilis multiplicate in the water used for biofloc formation: Growth, hemato-biochemistry, intestinal bacteria colonies, and bacterial resistance evaluations of Nile tilapia

Probiotics in the biofloc technology (BFT) system improve fish growth and immune response and promote a favorable intestinal microbiota balance. This study aimed to investigate the growth, hemato-biochemical parameters, bacterial resistance, and the number of intestinal bacteria colonies of Nile tilapia (6.23 g) reared in the BFT system with graded levels of Bacillus subtilis multiplicate (BSM) in the water. The multiplication of these microorganisms was performed in a biofactory. Fish were distributed into four different groups with graded BSM concentrations in the water of 0.00, 0.25, 0.50, and 0.75% (or 0; 750; 1500; and 2250 mL; called BSM0 (control), BSM25, BSM50, and BSM75, respectively). The experimental procedure had 45 days for growth performance evaluations and seven additional days of bacterial challenge with Aeromonas hydrophila. The experimental design was randomized into four treatments in triplicate (n = 20 fish per tank; initial stocking density of 0.50 kg m−3). Survival was 100% before and after the bacterial challenge. Increasing BSM in the BFT system had a positive linear effect on nitrite, nitrate, settled solids, hemoglobin, and hematimetric indices. BSM50 showed the highest specific growth rate, weight gain, intestinal total bacteria, and B. subtilis counts and the lowest feed conversion rate. In BSM50 and BSM75, liver glycogen levels and aspartate aminotransferase (AST) activity were higher and lower, respectively, than in the other treatments. Plasma total cholesterol, total proteins, albumin, and skin mucus total proteins and albumin were highest in BSM25. After the bacterial challenge, the number of lesions was lower in BSM75 than in the control group. In conclusion, we recommended BSM50 because it increased the growth performance and bacterial colonization in the intestine. It also decreased liver AST activity in Nile tilapia reared in the BFT system without compromising water quality and hematological and plasmatic parameters.

Micro-and nano-plastics induce kidney damage and suppression of innate immune function in zebrafish (Danio rerio) larvae

Aquatic environments serve as critical repositories for pollutants and have significantly accumulated micro- and nanoplastics (MNPs) due to the extensive production and application of plastic products. While the disease resistance and immunity of fish are closely linked to the condition of their aquatic habitats, the specific effects of nanoplastics (NPs) and microplastics (MPs) within these environments on fish immune functions are still not fully understood. The present study utilized zebrafish (Danio rerio) embryos and larvae as model organisms to examine the impacts of polystyrene NPs (100 nm) and MPs (5 μm) on fish immune responses. Our findings reveal that NPs and MPs tend to accumulate on the surfaces of embryos and within the intestines of larvae, triggering oxidative stress and significantly increasing susceptibility to Edwardsiella piscicida infection in zebrafish larvae. Transmission electron microscopy examined that both NPs and MPs inflicted damage to the kidney, an essential immune organ, with NPs predominantly inducing endoplasmic reticulum stress and MPs causing lipid accumulation. Transcriptomic analysis further demonstrated that both NPs and MPs significantly suppress the expression of key innate immune pathways, notably the C-type lectin receptor signaling pathway and the cytosolic DNA-sensing pathway. Within these pathways, the immune factor interleukin-1 beta (il1b) was consistently downregulated in both exposure groups. Furthermore, exposure to E. piscicida resulted in restricted upregulation of il1b mRNA and protein levels, likely contributing to diminished disease resistance in zebrafish larvae exposed to MNPs. Our findings suggest that NPs and MPs similarly impair the innate immune function of zebrafish larvae and weaken their disease resistance, highlighting the significant environmental threat posed by these pollutants.

Dietary microalgal-fabricated selenium nanoparticles improve Nile tilapia biochemical indices, immune-related gene expression, and intestinal immunity

BackgroundFeed supplements, including essential trace elements are believed to play an important role in augmenting fish immune response. In this context, selenium nanoparticles (SeNPs) in fish diets via a green biosynthesis strategy have attracted considerable interest. In this investigation, selenium nanoparticles (SeNPs, 79.26 nm) synthesized from the green microalga Pediastrum boryanum were incorporated into Nile tilapia diets to explore its beneficial effects on the immune defense and intestinal integrity, in comparison with control basal diets containing inorganic Se source. Nile tilapia (No. 180, 54–57 g) were fed on three formulated diets at concentrations of 0, 0.75, and 1.5 mg/kg of SeNPs for 8 weeks. After the trial completion, tissue bioaccumulation, biochemical indices, antioxidant and pro-inflammatory cytokine-related genes, and intestinal histological examination were analyzed.ResultsOur finding revealed that dietary SeNPs significantly decreased (P < 0.05) serum alkaline phosphatase (ALP), lactate dehydrogenase (LDH), and cholesterol, while increasing (P < 0.05) high-density lipoproteins (HDL). The Se concentration in the muscle tissues showed a dose-dependent increase. SeNPs at a dose of 1.5 mg/kg significantly upregulated intestinal interleukin 8 (IL-8) and interleukin 1 beta (IL-1β) gene transcription compared with the control diet. Glutathione reductase (GSR) and glutathione synthetase (GSS) genes were significantly upregulated in both SeNPs-supplemented groups compared with the control. No apoptotic changes or cell damages were observed as indicated by proliferating cell nuclear antigen (PCNA) and caspase-3 gene expression and evidenced histopathologically. SeNPs supplementation positively affects mucin-producing goblet cells (GCs), particularly at dose of 1.5 mg/kg.ConclusionTherefore, these results suggest that Green synthesized SeNPs supplementation has promising effects on enhancing Nile tilapia immunity and maintaining their intestinal health.

Characterization and functional analysis of SOCS9 from orange-spotted grouper (Epinephelus coioides) during virus infection

The suppressor of cytokine signaling (SOCS) proteins family have twelve members including eight known mammalian SOCS members (CISH, SOCS1-7) and four new discovery members (SOCS3b, SOCS5b, SOCS8 and SOCS9) that is regarded as a classic feedback inhibitor of cytokine signaling. Although the function of the mammalian SOCS proteins have been well studied, little is known about the roles of SOCS in fish during viral infection. In this study, the molecular characteristics of SOCS9 from orange-spotted grouper (Epinephelus coioides, EcSOCS9) is investigated. The EcSOCS9 protein encoded 543 amino acids with typical SH2 (389-475aa) and SOCS_box (491-527aa), sharing high identities with reported fish SOCS9. EcSOCS9 was expressed in all detected tissues and highly expressed in kidney. After red-spotted grouper nervous necrosis virus (RGNNV) infection, the expression of EcSOCS9 was significantly induced in vitro. Furthermore, EcSOCS9 overexpression enhanced RGNNV replication, promoted virus-induced mitophagy that evidenced by the increased level of LC3-Ⅱ, BCL2, PGAM5 and decreased level of BNIP3 and FUNDC1. Besides, EcSOCS9 overexpression suppressed the expression levels of ATP6, CYB, ND4, ATP level and induced ROS level. The expression levels of interferon (IFN) related factors (IRF1, IRF3, IRF7, P53), inflammatory factors (IL1-β, IL8, TLR2, TNF-α) and IFN-3, ISRE, NF-κB, AP1 activities were also reduced by overexpressing EcSOCS9. These date suggests that EcSOCS9 impacts RGNNV infection through modulating mitophagy, regulating the expression levels of IFN- related and inflammatory factors, which will expand our understanding of fish immune responses during viral infection.

Are fish immunocompetent enough to face climate change?

Ongoing climate change has already been associated with increased disease outbreaks in wild and farmed fish. Here, we evaluate the current knowledge of climate change-related ecoimmunology in teleosts with a focus on temperature, hypoxia, salinity and acidification before exploring interactive effects of multiple stressors. Our literature review reveals that acute and chronic changes in temperature and dissolved oxygen can compromise fish immunity which can lead to increased disease susceptibility. Moreover, temperature and hypoxia have already been shown to enhance the infectivity of certain pathogens/parasites and to accelerate disease progression. Too few studies exist that have focussed on acidification, but direct immune effects seem to be limited while salinity studies have led to contrasting results. Likewise, multi-stressor experiments essential for unravelling the interactions of simultaneously changing environmental factors are still scarce. This ultimately impedes our ability to estimate to what extent climate change will hamper fish immunity. Our review about epigenetic regulation mechanisms highlights the acclimation potential of the fish immune response to changing environments. However, due to the limited number of epigenetic studies, overarching conclusions cannot be drawn. Finally, we provide an outlook on how to better estimate the effects of realistic climate change scenarios in future immune studies in fish.

Amphiprion clarkii DDX41 modulates fish immune responses: Characterization by expression profiling, antiviral assay, and macrophage polarization analysis

DDX41, a member of the DEAD-box helicase family, serves as a vital cytosolic DNA sensor and plays a pivotal role in controlling the activation of type I interferon responses in mammals. However, the functional aspects of fish DDX41 remain relatively unexplored. In this study, we identified and characterized the DDX41 gene in Amphiprion clarkii transcriptomes and designated the gene as AcDDX41. The complete open reading frame of AcDDX41 encoded a putative protein comprising 617 amino acids. Notably, the predicted AcDDX41 protein shared several structural features that are conserved in DDX41, including DEXDc, HELICc, and zinc finger domains, as well as conserved sequence "Asp-Glu-Ala-Asp (D-E-A-D).” AcDDX41 exhibited the highest sequence homology (99.68 % similarity) with DDX41 from Acanthochromis polyacanthus. Phylogenetic analysis revealed that DDX41s from fish formed a branch distinct from that in other animals. All investigated tissues were shown to express AcDDX41 constitutively, with blood showing the highest expression levels, followed by the brain. Furthermore, AcDDX41 expression was significantly induced upon stimulation with poly I:C, lipopolysaccharide, and Vibrio harveyi, indicating its responsiveness to immune stimuli. We confirmed the antiviral function of AcDDX41 by analyzing gene expression and viral replication during viral hemorrhagic septicemia virus infection. Additionally, using a luciferase reporter assay, we validated the ability of AcDDX41 to activate the NF-κB signaling pathway upon stimulation with poly I:C. Finally, AcDDX41 influenced cytokine gene expression and played a regulatory role in macrophage M1 polarization in RAW 264.7 cells. Collectively, these results highlight the significance of AcDDX41 as an immune-related gene that contributes substantially to antiviral defense and regulation of NF-κB activity.