Fish Immunity Research Articles

The composition and unrevealed immune role of non-RLR DExD/H box RNA helicases in fish

The large superfamily of DExD/H box RNA helicases are involved in various life processes, such as RNA metabolism, transcriptional regulation, translation, tumorigenesis, cell cycle, and viral infection, and RIG-like receptors (RLRs) in the superfamily have been confirmed with crucial roles in viral infection by recognizing viral RNA. In this review, non-RLR DExD/H box RNA helicases were possibly summarized in relation with their composition and antiviral immune responses in teleost, with at least 52 genes in the helicase subfamily. Compared with mammals, most DExD/H box RNA helicases in teleost are conservatively present, but some are present in a fish-specific gene duplication manner or have been lost in evolution, which may imply the obvious compositional difference in fish. The comparison in innate immune roles of mammalian and teleost DExD/H box RNA helicases indicated that DDX3a, DDX3b, DHX9, DDX41, DDX43 are functional positively in anti-viral/bacterial immunity in fish, while DDX1, DDX3a, DDX5, DDX19, DDX23 negatively in the immunity. In the future, the composition, possible immune recognition, signalling and interaction with other immune pathways, as well as other biological functions are all of significant importance for research, which may contribute to the development of disease prevention and control strategies in aquaculture.

Single-cell transcriptome landscape of the kidney reveals potential innate immune regulation mechanisms in hybrid yellow catfish after Aeromonas hydrophila infection

Aeromonas hydrophila, the pathogen that is the causative agent of motile Aeromonas septicemia (MAS) disease, commonly attacks freshwater fishes, including yellow catfish (Pelteobagrus fulvidraco). Although the kidney is one of the most important organs involved in immunity in fish, its role in disease progression has not been fully elucidated. Understanding the cellular composition and innate immune regulation mechanisms of the kidney of yellow catfish is important for the treatment of MAS. In this study, single-cell RNA sequencing (scRNA-seq) was performed on the kidney of hybrid yellow catfish (Pelteobagrus fulvidraco ♀ × Pelteobagrus vachelli ♂) after A. hydrophila infection. Nine types of kidney cells were identified using marker genes, and a transcription module of marker genes in the main immune cells of hybrid yellow catfish kidney tissue was constructed using in-situ hybridization. In addition, the single-cell transcriptome data showed that the differentially expressed genes of macrophages were primarily enriched in the Toll-like receptor and Nod-like receptor signaling pathways. The expression levels of genes involved in these pathways were upregulated in macrophages following A. hydrophila infection. Transmission electron microscopy and TUNEL analysis revealed the cellular characteristics of macrophages before and after A. hydrophila infection. These data provide empirical support for in-depth research on the role of the kidney in the innate immune response of hybrid yellow catfish.

Immune response and protection efficacy of formalin-killed vaccines against Streptococcus iniae in four-finger threadfin Eleutheronema tetradactylum.

Four-finger threadfin, Eleutheronema tetradactylum farming in southern Taiwan has been facing disease problems caused by Streptococcus iniae since 2018. The development of a vaccine against infectious S. iniae in the cultured threadfin industry is necessary. Thus, this study aimed to examine the efficacy of threadfin immunized formalin-killed cells (FKC) from S. iniae GSI-111 for 42 days post-vaccination (dpv) using two doses of FKC alone (a booster at 14 dpv) as group A, and FKC mixed with ISA763A adjuvant using a single dose as group B or double doses as group C. Immunoglobulin (Ig)-M was purified from threadfin, and rabbit anti-threadfin IgM polyclonal antibodies were used to detect antibody level in immunized fish; the vaccinated group A displayed higher levels at 3 dpv and all vaccinated treatments demonstrated high antibody levels between 14 and 42 dpv. All vaccine groups showed significantly higher values of lysozyme activity at 42 dpv compared with the control group; the vaccinated A group peaked at 14 dpv. The expression profiles of pro-inflammatory and immune-related genes, TNF-α, IL-12A, and C2 were upregulated at 3 dpv, while CD8A and chemokine receptor CXCR4 were upregulated at 42 dpv. Finally, the threadfins were challenged with S. iniae at 42 dpv. The average relative percent survival was 96% for vaccination A and B treatments, and 100% for vaccination C treatment. In summary, this study demonstrated that FKC vaccines whether formulated with an adjuvant could stimulate immune response and effective protect threadfins against S. iniae infection.

Utilization of recombinant Chlorella expressing dsRNA for protection against grouper nervous necrosis virus

In mammals and fish, dsRNA can induce the type I interferon (IFN-I), leading to the expression of antiviral and immune-related genes. The use of microalgae expressing dsRNA as an oral delivery system to activate innate immunity in fish has not been documented. In this study, wild Chlorella sorokiniana was transformed with NNV (nervous necrosis virus) RdRp and GIV (grouper iridovirus) ORF086R dsRNA expression vectors. The recombinant Chlorella strains effectively protected pearl gentian groupers (Epinephelus fuscoguttatus♀ × Epinephelus lanceolatus♂) against NNV and reduced viral titers. The survival rates of the NNV RdRp and GIV ORF086R dsRNA treatment groups increased by 32 % and 38 %, respectively, compared with that of the control group. These findings indicate that recombinant Chlorella has the potential to be used as an oral delivery strategy for protection against NNV disease in groupers.

Characterization of the impact of dietary immunostimulant CpG on the expression of mRNA biomarkers involved in the immune responses in Atlantic salmon (Salmo salar)

Infectious diseases have significantly impacted Atlantic salmon aquaculture worldwide. Modulating fish immunity with immunostimulant-containing functional feeds could be an effective strategy in mitigating disease problems. Previously, we characterized the impact of polyriboinosinic polyribocytidylic acid (pIC) and formalin-killed typical Aeromonas salmonicida bacterin on miRNA expression in Atlantic salmon fed a commercial diet with and without immunostimulant CpG. A set of miRNA biomarkers of Atlantic salmon head kidney responding to pIC and/or bacterin immune stimulations was identified (Xue et al., 2019) [1]. Herein, we report a complementary qPCR study that investigated the impact of the pIC, bacterin and dietary CpG on the expression of immune-relevant mRNAs (n = 31) using the same samples as in the previous study (Xue et al., 2019) [1]. Twenty-six of these genes were predicted target transcripts of the pIC- and/or bacterin-responsive miRNAs identified in the earlier study. The current data showed that pIC and/or bacterin stimulations significantly modulated the majority of the qPCR-analyzed genes involved in various immune pathways. Some genes responded to both stimulations (e.g. tnfa, il10rb, ifng, irf9, cxcr3, campb) while others appeared to be stimulation specific [e.g. irf3, irf7a, il1r1, mxa, mapk3 (pIC only); clra (bacterin only)]. A. salmonicida bacterin stimulation produced a strong inflammatory response (e.g. higher expression of il1b, il8a and tnfa), while salmon stimulated with pIC showed robust interferon responses (both type I and II). Furthermore, the current data indicated significant down-regulation of immune-relevant transcripts (e.g. tlr9, irf5, il1r1, hsp90ab1, itgb2) by dietary immunostimulant CpG, especially among pre-injection and PBS-injected fish. Together with our prior miRNA study, the present research provided complementary information on Atlantic salmon anti-viral and anti-bacterial immune responses and on how dietary CpG may modulate these responses.

Oleic acid enriched diet affects the metabolome composition of the hybrid grouper infected with vibriosis.

This study focuses in investigating the fatty acid contents of surviving infected hybrid grouper fed with oleic acid immunostimulant. After a 6-week feeding trial, Epinephelus fuscoguttatus × Epinephelus lanceolatus fingerlings were infected with Vibrio vulnificus. One week after bacterial challenge, fish oil was extracted from body tissue of surviving infected fingerlings using the Soxhlet extraction method. The extracted samples were then sent for GC-MS analysis. The raw GC-MS data were analyzed using software programs and databases (i.e., MetaboAnalyst, SIMCA-P, NIST Library, and KEGG). A total of 39 metabolites were putatively identified, with 18 metabolites derived from the fatty acid group. Our further analysis revealed that most metabolites were highly abundant in the oleic acid dietary samples, including oleic acid (4.56%), 5,8,11-eicosatrienoic acid (3.45%), n-hexadecenoic acid (3.34%), cis-erucic acid (2.76%), and 9-octadecenoic acid (2.5%). Worthy of note, we observed a greater abundance of α-linoleic acid (15.57%) in the control diet samples than in the oleic acid diet samples (14.59%) with no significant difference in their results. The results obtained from this study revealed that surviving infected hybrid grouper expressed more immune-related fatty acids due to the effect of oleic acid immunostimulant. Therefore, in this study, we propose oleic acid as a potential immunostimulant in enhancing fish immunity in aquaculture industry.

Eco-innovative aquafeeds biofortified with Asparagopsis taxiformis to improve the resilience of farmed white seabream (Diplodus sargus) to marine heatwave events

Extreme weather events, like marine heatwaves (MHWs), are becoming more frequent and severe due to climate change, posing several challenges to marine ecosystems and their services. As disease outbreaks are often prompted by these acute phenomena, it is essential to develop eco-innovative strategies that can efficiently improve farmed fish resilience, especially under sub-optimal rearing conditions, thereby ensuring a sustainable aquaculture production.This study aimed to unveil farmed juvenile white seabream (Diplodus sargus, 28.50 ± 1.10 g weight, n = 150) immune and antioxidant responses under a category II MHW in the Mediterranean Sea (+4 °C, 8 days of temperature increase plus 15 days of plateau at the peak temperature) and to investigate whether a 30 days period of prophylactic biofortification with Asparagopsis taxiformis (1.5 %, 3 % and 6 %) enhanced fish resilience to these extreme events. Several biomarkers from different organization levels (individual, cellular, biochemical and molecular) were assessed upon 30 days of biofortification (T30), exposure (after 8 days of temperature increase + 15 days at peak temperature, T53) and recovery (8 days of temperature decrease, T61) from the MHW.Results showed that MHW negatively affected the fish physiological status and overall well-being, decreasing specific growth rate (SGR) and haematocrit (Ht) and increasing erythrocyte nuclear abnormalities (ENAs) and lipid peroxidation (LPO). These adverse effects were alleviated through biofortification with A. taxiformis. Seaweed inclusion at 1.5 % was the most effective dose to minimize the severity of MHW effects, significantly improving immune responses of D. sargus (i.e. increased levels of immunoglobulin M, peroxidase activity and lysozyme expression) and modulating antioxidant responses (i.e. decreased LPO, catalase and glutathione S-transferase activity). These findings confirm that A. taxiformis is a functional ingredient of added value to the aquaculture industry, as its inclusion in marine fish diets can beneficially modulate fish immunity and resilience under optimal and adverse rearing conditions.

Effects of dietary puerarin on growth, digestive enzyme, antioxidant capacity, immune and liver health of Acanthopagrus latus

This study was conducted to investigate the effects of puerarin on growth, digestive enzymes, antioxidant capacity, immunity and liver health of Acanthopagrus latus. Four diets were formulated: a control diet (C) and C supplemented with 200, 400, and 600 mg/kg puerarin (CP2, CP4, and CP6, respectively) and a eight-week feeding trial was conducted of fish. The results showed that the addition of 400 mg/kg puerarin significantly increased weight gain (WG), specific growth rate (SGR), and decreased the feed conversion ratio (FCR) compared to C group. Dietary supplementation with 600 mg/kg puerarin significantly increased lipase (LPS) activity compared to the C group. The addition of 200 mg/kg puerarin significantly reduced low-density lipoprotein cholesterol (LDL-C) and 400 mg/kg puerarin significantly reduced total cholesterol (T-CHO), triglycerides (TG) and HDL-C compared to the C group. Dietary supplementation with 400 mg/kg puerarin significantly increased serum and liver glutathione (GSH) activity and decreased malondialdehyde (MDA) content compared to the C group. Addition of 400 mg/kg puerarin significantly increased liver catalase (CAT) activity compared to the C group. Supplementation of 600 mg/kg and 400 mg/kg of puerarin significantly increased serum alkaline phosphatase (AKP) and lysozyme (LZM) activities, respectively. Compared to the C group, the addition of 200 mg/kg of puerarin significantly increased the activities of acid phosphatase (ACP) and alkaline phosphatase (AKP) in the liver. CP4-feeding significantly upregulated the expression of nrf2, ho-1, and gclc while downregulating the expression of keap1 compared to the C group. The addition of puerarin significantly reduced the expression of tnf-α and il-6 compared to the C group. Supplementation of 200 mg/kg puerarin significantly reduced the expression of bax compared to the C group. In conclusion, dietary supplementation with puerarin had positive effects on the growth, digestive enzymes, antioxidant capacity, immunity, and liver health of fish, particularly at 503.5 mg/kg.

Dietary administration of green macroalgae (Ulva intestinalis) on growth performance, serum immune parameters, and gene expression in Common carp (Cyprinus carpio)

Abstract The purpose of this experiment was to assess the effects of the green macroalgae (Ulva intestinalis) on growth performance, immune parameters of serum and mucus, liver enzymes and the expression of genes related to growth (GH and IGF-1), and immunity (IL1-β and Lyz) in common carp (Cyprinus carpio). The test was carried out in eight weeks with the treatments supplemented with 0 (control), 0.25%, 0.5%, and 1% macroalgae and three replications for each group. At the end of the course, growth indices, serum and mucus total protein, total immunoglobulin, lysozyme, and liver enzymes including alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase were evaluated. Additionally, the expression of growth (GH and IGF-1) and Immunity (IL1-β and Lyz) genes was evaluated using real-time PCR in the brain, liver, and intestine. Based on the results, a significant difference was observed in the levels of total protein, total immunoglobulin, and mucus lysozyme in the fish that received 1% U. intestinalis compared to the control group (P<0.05). In addition, the amount of total protein, total immunoglobulin, and lysozyme in the control group and the other treatments represented a significant difference (P<0.05). Although the initial weight did not show a significant difference among the treatments (P>0.05), the final growth parameters significantly varied in different treatments, with the highest final weight observed in fish fed with 0.25% algae (P<0.05). The results of the expression of immune genes lysozyme (Lyz) and interleukin-1 (IL-1) indicated a significant difference with the control group (P<0.05), representing an increasing pattern with the rising percentage of macroalgae (P<0.05). The supplement was also found effective in promoting the expression of growth hormone (GH) and insulin-like growth factor (IGF-1) compared to the control fish (P<0.05), revealing an increasing pattern for the IGF-1 gene with the elevated level of the supplement. In general, according to the results of the present study, U.intestinalis can be recommended in carp aquaculture, most preferably at the level of 1% of daily feed, as it could significantly enhance the growth and innate immunity of fish.

Fish HERC7: Phylogeny, Characterization, and Potential Implications for Antiviral Immunity in European Sea Bass.

E3 ubiquitin ligases, key components of the ubiquitin proteasome system, orchestrate protein degradation through ubiquitylation and profoundly impact cellular biology. Small HERC E3 ligases (HERC3-6) have diverse functions in mammals, including roles in spermatogenesis, protein degradation, and immunity. Until now, only mammals' HERC3, HERC5, and HERC6 are known to participate in immune responses, with major involvement in the antiviral response. Interestingly, an exclusive HERC7 has been characterized in fish showing great molecular conservation and antiviral roles. Thus, this study identifies and characterizes the herc7 gene in the European sea bass teleost. The European sea bass herc7 gene and the putative protein show good conservation of the promoter binding sites for interferons and the RCC1 and HECT domains characteristic of HERC proteins, respectively. The phylogenetic analysis shows a unique cluster with the fish-exclusive HERC7 orthologues. During ontogeny, the herc7 gene is expressed from 3 days post-fertilization onwards, being constitutively and widely distributed in adult tissues. In vitro, stimulated leucocytes up-regulate the herc7 gene in response to mitogens and viruses, pointing to a role in the immune response. Furthermore, sea bass herc7 expression is related to the interferon response intensity and viral load in different tissues upon in vivo infection with red-grouper betanodavirus (RGNNV), suggesting the potential involvement of fish HERC7 in ISGylation-based antiviral activity, similarly to mammalian HERC5. This study broadens the understanding of small HERC proteins in fish species and highlights HERC7 as a potential contributor to the immune response in European sea bass, with implications for antiviral defense mechanisms. Future research is needed to unravel the precise actions and functions of HERC7 in teleost fish immunity, providing insights into direct antiviral activity and viral evasion.

The TAK1/JNK axis participates in adaptive immunity by promoting lymphocyte activation in Nile tilapia

The transforming growth factor beta-activated kinase 1 (TAK1)/c-Jun N-terminal kinase (JNK) axis is an essential MAPK upstream mediator and regulates immune signaling pathways. However, whether the TAK1/JNK axis harnesses the strength in regulation of signal transduction in early vertebrate adaptive immunity is unclear. In this study, by modeling on Nile tilapia (Oreochromis niloticus), we investigated the potential regulatory function of TAK1/JNK axis on lymphocyte-mediated adaptive immune response. Both OnTAK1 and OnJNK exhibited highly conserved sequences and structures relative to their counterparts in other vertebrates. Their mRNA was widely expressed in the immune-associated tissues, while phosphorylation levels in splenic lymphocytes were significantly enhanced on the 4th day post-infection by Edwardsiella piscicida. In addition, OnTAK1 and OnJNK were significantly up-regulated in transcriptional level after activation of lymphocytes in vitro by phorbol 12-myristate 13-acetate plus ionomycin (P + I) or PHA, accompanied by a predominant increase in phosphorylation level. More importantly, inhibition of OnTAK1 activity by specific inhibitor NG25 led to a significant decrease in the phosphorylation level of OnJNK. Furthermore, blocking the activity of OnJNK with specific inhibitor SP600125 resulted in a marked reduction in the expression of T-cell activation markers including IFN-γ, CD122, IL-2, and CD44 during PHA-induced T-cell activation. In summary, these findings indicated that the conserved TAK1/JNK axis in Nile tilapia was involved in adaptive immune responses by regulating the activation of lymphocytes. This study enriched the current knowledge of adaptive immunity in teleost and provided a new perspective for understanding the regulatory mechanism of fish immunity.

The Immunostimulatory Potential and Resistance Aeromonas hydrophila of Pineapple Peel Extract in Nile Tilapia (Oreochromis niloticus)

This study described the efficiency of pineapple peel extract (PPE) in increasing the immunity of Nile tilapia (Oreochromis niloticus) and in inhibiting Aeromonas hydrophila infections. The PPE concentrations used in this study were: 62.5, 125, and 250 mg/mL. 0.1 mL of PPE was administered via intraperitoneal injection into the fish. On day 7, fish was intraperitoneally injected with 0.1 mL A. hydrophila (density 108 CFU/mL). Hematology and biochemical serum parameters were observed on day 1 and 7 after injected with PPE and day 7 and 14 post-challenge with A. hydrophila. The results indicated that, red blood cells, white blood cells, and hematocrit of PPE-injected fish were significantly higher than those in the control group (p<0.05). Alkaline phosphatase, aspartate transaminase, and alanine transaminase in the fish groups receiving PPE were lower than those of the control group. After challenge test, fish injected with 125 mg/mL PPE concentration was able to significantly reduce the mortality rate compare to control (from 80.50% to 47.22%). It can be concluded that PPE was effective in preventing A. hydrophila infections, and had a positive impact on the immunity of fish. So that pineapple is an alternative plant that can be used to improve fish health.

Effects of puerarin on growth, liver immunity and antioxidant capacity of yellowfin seabream (Acanthopagrus latus) under oxidized fish oil stress

Puerarin, an isoflavone, exhibits protective effects against liver damage. This study investigated the effects of puerarin on the growth, liver immunity, and antioxidant capacity of yellowfin seabream fed with oxidized fish oil. A total of 135 yellowfin seabream (13.00±0.05 g) were randomly divided into nine tanks (15 fish per tank), and fed with three types of diets for 56 days: a normal control fed with 6 % fresh fish oil (NC), an experimental control fed with 6 % oxidized fish oil (OFO), and a treatment fed with 6 % oxidized fish oil and supplemented with 400 mg/kg puerarin (OFP). Results showed, oxidized fish oil decreased the growth of fish, caused liver damage, and suppressed the fish's immunity. Compared to the NC group, the weight gain (WG) and specific growth rate (SGR) of the fish in the OFO group were significantly reduced; the activities of superoxide dismutase (SOD) and catalase (CAT) in serum were significantly decreased; liver morphology showed loose cytoplasm with a large amount of fatty degeneration; the lysozyme (LZM) activity in serum and liver was significantly reduced. On the other hand, compared to the NC and OFO groups, the WG and SGR of fish in the OFP group were significantly improved. Additionally, compared to the OFO group, the serum SOD and liver CAT activities in the fish of the OFP group were significantly increased, and the MDA content in serum and liver was significantly reduced. The extensive fatty degeneration in the liver was alleviated. The LZM activity in the serum and liver of fish in the OFP group was significantly higher than that in the OFO group, returning to the levels of the NC group. Meanwhile, puerarin significantly enhanced the expression of Nrf2. In conclusion, puerarin alleviated the adverse reactions induced by oxidized fish oil and promoted the growth of yellowfin seabream.

LECT2 mediates antibacterial immune response induced by Nocardia seriolae infection in the northern snakehead

Leukocyte-derived chemotaxin-2 (LECT2) is a multifunctional immunoregulator that plays several pivotal roles in the host's defense against pathogens. This study aimed to elucidate the specific functions and mechanisms of LECT2 (CaLECT2) in the northern snakehead (Channa argus) during infections with pathogens such as Nocardia seriolae (N. seriolae). We identified CaLECT2 in the northern snakehead, demonstrating its participation in the immune response to N. seriolae infection. CaLECT2 contains an open reading frame (ORF) of 459 bp, encoding a peptide of 152 amino acids featuring a conserved peptidase M23 domain. The CaLECT2 protein shares 62%–84 % identities with proteins from various other fish species. Transcriptional expression analysis revealed that CaLECT2 was constitutively expressed in all examined tissues, with the highest expression observed in the liver. Following intraperitoneal infection with N. seriolae, CaLECT2 transcription increased in the spleen, trunk kidney, and liver. In vivo challenge experiments showed that injecting recombinant CaLECT2 (rCaLECT2) could protect the snakehead against N. seriolae infection by reducing bacterial load, enhancing serum antibacterial activity and antioxidant capacity, and minimizing tissue damage. Moreover, in vitro analysis indicated that rCaLECT2 significantly enhanced the migration, respiratory burst, and microbicidal activity of the head kidney-derived phagocytes. These findings provide new insights into the role of LECT2 in the antibacterial immunity of fish.

Functional insights of digestion, absorption, and immunity in different segments of the intestine in Hemibarbus labeo from transcriptomic analysis

The intestine is an important organ for food digestion and absorption and body immunity in fish. In this study, we investigated the abundance of transcripts from different segments of the intestinal tract using transcriptome sequencing technology in Hemibarbus labeo, to provide functional insights into digestion, absorption, and immunity in the anterior intestine (AI), middle intestine (MI), and posterior intestine (PI). We found 5646 differentially expressed genes (DEGs), which were significantly enriched to GO terms of carbohydrate metabolic process, transmembrane transport, iron ion binding, lipid metabolic process, and KEGG pathway of fat digestion and absorption, mineral absorption, protein digestion and absorption, vitamin digestion and absorption, indicating that the digestion and absorption function of food is different in AI, MI, and PI. In practice, most genes, enriched in the KEGG pathway for digestion and absorption of nutrients, are upregulated in AI and MI, indicating stronger roles for food digestion and absorption in these segments. Furthermore, we found that genes involved in the KEGG pathway of lysosome and endocytosis pathway are upregulated in PI, suggesting stronger antigen-presenting capabilities in PI. However, some cytokine receptor genes, including ccr4, cxcr2, tnfrsf9, il6r, csf3r, and cxcr4, are highly expressed in AI, reflecting the regional immune specialization in different segments. This study provides functional insights into digestion, absorption, and immunity in different segments of the intestine and supports the regional functional specialization within different segments of the intestine in H. labeo.

Immune protection of grass carp by oral vaccination with recombinant Bacillus methylotrophicus expressing the heterologous tolC gene

In the field of aquaculture, the enhancement of animal health and disease prevention is progressively being tackled using alternatives to antibiotics, including vaccines and probiotics. This study was designed to evaluate the potential of a recombinant Bacillus methylotrophicus, engineered to express the outer membrane channel protein TolC of Aeromonas hydrophila AH3 and the green fluorescent protein GFP, as an oral vaccine. Initially, the genes encoding tolC and GFP were cloned into a prokaryotic expression system, and anti-TolC mouse antiserum was generated. Subsequently, the tolC gene was subcloned into a modified pMDGFP plasmid, which was transformed into B. methylotrophicus WM-1 for protein expression. The recombinant B. methylotrophicus BmT was then administered to grass carp via co-feeding, and its efficacy as an oral vaccine was assessed. Our findings demonstrated successful expression of the 55 kDa TolC and 28 kDa GFP proteins, and the preparation of polyclonal antibodies with high specificity. The BmT exhibited stable expression of the GFP-TolC fusion protein and excellent genetic stability. Following oral immunization, significant elevations were observed in serum-specific IgM levels and the activities of acid phosphatase (ACP), alkaline phosphatase (AKP), superoxide dismutase (SOD), and lysozyme (LZM) in grass carp. Concurrently, significant upregulation of immune-related genes, including IFN-I, IL-10, IL-1β, TNF-α, and IgT, was noted in the intestines, head kidney, and spleen of the grass carp. Colonization tests further revealed that the BmT persisted in the gut of immunized fish even after a fasting period of 7 days. Notably, oral administration of BmT enhanced the survival rate of grass carp following A. hydrophila infection. These results suggest that the oral BmT vaccine developed in this study holds promise for future applications in aquaculture.

Sea water acclimation of rainbow trout (Oncorhynchus mykiss) modulates the mucosal transcript immune response induced by Vibrio anguillarum and Aeromonas salmonicida vaccine, and prevents further transcription of stress-immune genes in response to acute stress

Mucosal tissues appear to be more important in fish than in mammals due to living in a microbial-rich aquatic milieu, yet the complex interaction between the immune and the neuroendocrine system in these tissues remains elusive. The aim of this work was to investigate the mucosal immune response in immunized rainbow trout vaccinated with Alpha ject vaccine (bivalent), kept in fresh water (FW) or transferred to seawater (SW), and to evaluate their response to acute stress (chasing). Acute stress resulted in higher levels of plasma cortisol (Sham + Stress and Vaccine + Stress). A similar response was observed in skin mucus, but it was lower in Vaccine + Stress compared with stressed fish. With a few exceptions, minimal alterations were detected in the transcriptomic profile of stress-immune gene in the skin of vaccinated and stressed fish in both FW and SW. In the gills, the stress elicited activation of key stress-immune components (gr1, mr, β-ar, hsp70, c3, lysozyme, α-enolase, nadph oxidase, il1β, il6, tnfα, il10 and tgfβ1) in FW, but fewer immune changes were induced by the vaccine (nadph oxidase, il6, tnfα, il10 and igt) in both SW and FW. In the intestine, an array of immune genes was activated by the vaccine particularly those related with B cells (igm, igt) and T cells (cd8α) in FW with no stimulation observed in SW. Therefore, our survey on the transcriptomic mucosal response demonstrates that the immune protection conferred by the vaccine to the intestine is modulated in SW. Overall, our results showed: i) plasma and skin mucus cortisol showed no additional stress effect induced by prolonged SW acclimation, ii) the stress and immune response were different among mucosal tissues which indicates a tissue-specific response to specific antigens/stressor. Further, the results suggest that the systemic immune organs may be more implicated in infectious events in SW (as few changes were observed in the mucosal barriers of immunized fish in SW) than in FW.

Commensal Bacillus pumilus SE5-Derived Peptidoglycan and Lipoteichoic Acid Showed Synergistic Effects in Improving Growth, Immunity, and Intestinal Health of Grouper (Epinephelus coioides).

Commensal-derived peptidoglycan (PG) or lipoteichoic acid (LTA) can improve the growth, immunity, and intestinal health of fish, but it is not clear whether the two components have synergistic effects. To clarify this, grouper (Epinephelus coioides) was fed basal diet (CG) or diets containing 1.0 × 108CFU/g heat-inactivated SE5 (HIB), PG (21.30mg/kg), LTA (6.70mg/kg), mixture (PL1) of PG (10.65mg/kg) and LTA (3.35mg/kg), and mixture (PL2) of PG (21.30mg/kg) and LTA (6.70mg/kg). Improved growth performance and feed utilization were observed in groups PG, LTA, PL1, and PL2, and the optimum growth performance was recorded in group PL1. Furthermore, improved serum alkaline phosphatase (AKP) activity and immunoglobulin M (IgM) and complement C3 (C3) contents were observed in all treatments, and the AKP activity in group PL1 was significantly superior to that of groups PG and LTA. Although PG and LTA alone or in combination exert comparable effects on intestinal microbiota and physical structure, obviously enhanced intestinal protease activity was observed in group PL1. The combined efficacy of PL1 could further potentiate the immune response by modulating the nucleotide-binding oligomerization domain-containing protein 2 (NOD2) and upregulating the expression of antimicrobial peptides (epinecidin-1, hepcidin-1, and β-defensin) as well as IgM. At the same time, group PL1 could further mitigate intestinal inflammation by downregulating pro-inflammatory cytokines and upregulating anti-inflammatory cytokines. In conclusion, probiotic B. pumilus SE5-derived PG and LTA mixture (10.65mg/kg PG and 3.35mg/kg LTA) exhibits better potential for improving the growth performance, intestinal health, and immune function compared to another mixture (21.30mg/kg PG and 6.70mg/kg LTA) and PG or LTA alone in grouper.

Effect of Dietary Supplementation on the Growth and Immunity of Fish and Shellfish

With the rapid development of aquaculture, the shortage of high-quality dietary ingredients has become a critical problem limiting the sustainable development of aquaculture [...]

Optimum eicosapentaenoic acid + docosahexaenoic acid levels for farmed Atlantic salmon: closing the gap between science and commercial practice

The shift from fish oil to vegetable oil (VO) sources has lowered eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) levels in salmon aquafeeds. VOs are high in omega-6 and low in omega-3 essential fatty acids like EPA and DHA, crucial for fish metabolism and immunity. Algal oil (AO), with high EPA + DHA and lower omega-6 levels supports fish health and growth, but transferring lab-controlled conditions to real-world commercial farming remains a challenge. This study explored the benefits of high dietary EPA + DHA levels through a commercial farm (CF) study in Chile and a Big Data (BD) study in Norway. The CF study, involving 625,000 Atlantic salmon, compared standard feed with AO-supplemented feed. The latter resulted in improved health responses and better fillet quality. The BD study analyzed real data from 232.6 million fish, revealing that EPA + DHA levels > 8% reduce mortality variability by 21%, improve economic feed conversion ratio by 11%, and increase the likelihood of superior harvests by 27%, demonstrating productivity benefits. Both studies emphasize the advantages of feeds with EPA + DHA levels above typical industry practices, enhancing growth, health, and nutritional quality. Importantly, the BD study complements the CF study, bridging the gap between science and aquafarms, and providing evidence that diets with EPA + DHA > 8% offer biological performance benefits for farmers, regardless of farming environments.