Immunity In Rainbow Trout Research Articles

Molecular mechanism of TRIM32 in antiviral immunity in rainbow trout (Oncorhynchus mykiss)

TRIM family proteins are widely found in multicellular organisms and are involved in a wide range of life activities, and also act as crucial regulators in the antiviral natural immune response. This study aimed to reveal the molecular mechanism of rainbow trout TRIM protein in the anti-IHNV process. The results demonstrated that 99.1 % homology between the rainbow trout and the chinook salmon (Oncorhynchus tshawytscha) TRIM32. When rainbow trout were infected with IHNV, the TRIM32 was highly expressed in the gill, spleen, kidney and blood. Meanwhile, rainbow trout TRIM32 has E3 ubiquitin ligase activity and undergoes K29-linked polyubiquitination modifications dependent on the RING structural domain was determined by immunoprecipitation. TRIM32 could interact with the NV protein of IHNV and degrade NV protein through the ubiquitin-proteasome pathway, and was also able to activate NF-κB transcription, thereby inhibiting the replication of IHNV. Moreover, the results of the animal studies showed that the survival rate of rainbow trout overexpressing TRIM32 was 70.2 % which was significantly higher than that of the control group, and stimulating the body to produce high levels of IgM when the host was infected with the virus. In addition, TRIM32 can activate the NF-κB signalling pathway and participate in the antiviral natural immune response. The results of this study will help us to understand the molecular mechanism of TRIM protein resistance in rainbow trout, and provide new ideas for disease resistance breeding, vaccine development and immune formulation development in rainbow trout.

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.

Dietary supplementation of Chinese herbal medicines enhances the immune response and resistance of rainbow trout (Oncorhynchus mykiss) to infectious hematopoietic necrosis virus.

Rainbow trout is a widely farmed economical cold-water fish worldwide, but the prevalence of infectious hematopoietic necrosis virus (IHNV) presents a severe risk to the aquaculture industry, resulting in high mortality and huge economic losses. In this study, the impacts of different concentrations (0, 10, 20, and 30 g/kg) of Chinese herbal medicine mixture (CHMM) on the immune response and resistance of rainbow trout to IHNV infection were evaluated. The results show that CHMM noticeably increased (P < 0.05) T-SOD, CAT, AST, ALT, ACP, and AKP activities and decreased MDA content. NF-κB, TNF-α, IFN-β, IL-1β, JAK1, HSP70, and HSP90 expressions were significantly upregulated (P < 0.05) in all CHMMs, while SOCS2 expression was downregulated (P < 0.05). Following infection with IHNV, feeding rainbow trout with varying amounts of CHMM resulted in noticeably increased (P < 0.05) T-SOD, ACP, and AKP activities and significantly decreased (P < 0.05) MDA content and AST and ALT activities. TNF-α, IFN-β, IL-1β, HSP70, and HSP90 expressions were significantly upregulated (P < 0.05) in all CHMMs, while the expressions of JAK1 and SOCS2 were downregulated. The expression level of the IHNV G protein gene at a dosage of 20 g/kg was notably lower than that of the other CHMM feeding groups. This study provides a solid scientific basis for promoting CHMM as an immunostimulant for boosting antiviral immunity in rainbow trout.

Optimizing turmeric and green tea fermentation with Lactobacillus brevis to enhance growth performance, digestive enzymes, and immunity in rainbow trout

This study aimed to find the optimal fermentation technology of medicinal plants (turmeric, Curcuma longa and green tea, Camellia sinensis) mixed with Lactobacillus brevis (FML) and the effects of FML on the growth performance, immune response, and anti-microbial ability of rainbow trout fingerlings. To optimize the fermentation process, response to surface methodology (RSM) was applied. The optimal fermentation conditions were 8% probiotic and 25-h fermentation time. Fish (n = 600; 9.37 ± 0.24 g initial weight) was subjected to a feeding experiment involving five different diets. These diets included a control group without any additives as well as groups supplemented with various amounts of FML: 0.2% (FML1), 0.5% (FML2), 0.8% (FML3), and 1% (FML4) for a period of 60 days. Afterwards, a subset of 15 fish was selected from each tank and exposed to Yersinia ruckeri for 14 days. After the feeding trial, the growth indices significantly increased in FML-added groups (p < 0.05). The protease activity markedly increased in all FML-treated groups (except for FML1) compared to the control group (p < 0.05). Moreover, the serum bactericidal activity, immunoglobulin, total protein (TP), and globulin levels increased in FML3 and FML4 groups compared to those receiving the control and FML1 diets (p < 0.05). The skin mucus alkaline phosphatase and serum TP levels significantly increased in the fish fed with FML3 and FML4 diets compared to other treatments (p < 0.05). The highest sivival rate was observed in FML4 (83.3%) followed by FML3 (66.7%) group. Overall, dietary FML, especially in FML4 diet, has a beneficial role to ameliorate growth rate, immune functions, and disease resistance against Y. ruckeri in rainbow trout.

Growth promoting and immunomodulatory effects of dietary Moringa oleifera leaf powder in rainbow trout (Oncorhynchus mykiss)

This study aimed to manifest the dietary effect of Moringa oleifera (MO) leaf powder on growth performance and immunity in rainbow trout before and after Aeromonas hydrophila infection. The fish (N = 360; 35.49 ± 0.50 g) were fed with incremental levels of MO at 0, 10, 25, and 50 g/kg for eight weeks and then challenged with A. hydrophila for 10 days in triplicates. The final weight (114.6 g) and feed conversion ratio (1.28) were significantly decreased in MO-50 compared to other MO-added groups (P < 0.05). In the unchallenged fish, the total white blood cells (WBC), lymphocyte, and neutrophil population size did not change between the experimental and the control groups (P < 0.05), while after the bacterial infection, the number of circulating lymphocytes and WBC were significantly increased in both MO-25 and MO-50 groups compared to the control group. Before the challenge test, the expression level of lysozyme gene in the head kidney was significantly (P < 0.05) increased in all MO-added groups, while the serum and skin mucus lysozyme, bactericidal, and complement activities were notably increased in MO-25 group. A similar trend was observed in the expression levels of IL-1β and TNF-1α genes in the head kidney of MO-added groups, while the total mucus immunoglobulin and protein levels were elevated in both MO-25 and MO-50 groups. The expression levels of SOD, CAT, and GPx genes were markedly down-regulated in MO-25 compared to the control group pre- and post-challenge test. The fish survival rate after challenging with A. hydrophila significantly increased from 46.7% in the control group to 76.7% in MO-25 group. In conclusion, using the supplemental diets with MO for rainbow trout at 19.3–25.0 and 27.5–30.5 g/kg is recommended based on the polynomial regression analyses to accelerate growth performance and provide immunostimulation, respectively.

Probiotics Mediate Intestinal Microbiome and Microbiota-Derived Metabolites Regulating the Growth and Immunity of Rainbow Trout (Oncorhynchus mykiss).

Emerging evidence confirms using probiotics in promoting growth and immunity of farmed fish. However, the molecular mechanisms underlying the host-microbiome interactions mediated by probiotics are not fully understood. In this study, we used rainbow trout (Oncorhynchus mykiss) as a model to investigate the internal mechanisms of host-microbiome interactions influenced by two probiotic bacteria, Bacillus velezensis and Lactobacillus sakei. We carried out experiments, including intestinal histology, serum physiology, and transcriptome and combined intestinal microbiome and metabolite profiling. Our results showed that both probiotics had a positive effect on growth, immunity, serum enzyme activity, the gut microbiome, and resistance to Aeromonas salmonicida in rainbow trout. Moreover, the intestinal microbial structure was reshaped with increased relative abundance of potential beneficial bacteria, such as Ruminococcus, Lachnospiraceae ucg-004, Leptotrichia, Bacillus coagulans, Porphyromonadaceae, Anaerococcus, and Photobacterium in the B. velezensis group and Paenibacillaceae and Eubacterium hallii in the L. sakei group. Metabolomic profiling and transcriptome analysis revealed upregulated metabolites as biomarkers, i.e., sucrose and l-malic acid in the B. velezensis group, and N-acetyl-l-phenylalanine, N-acetylneuraminic acid, and hydroxyproline in the L. sakei group. Additionally, a multiomics combined analysis illustrated significant positive correlations between the relative abundance of microflora, metabolites, and gene expression associated with immunity and growth. This study highlights the significant role of probiotics as effectors of intestinal microbial activity and shows that different probiotics can have a species-specific effect on the physiological regulation of the host. These findings contribute to a better understanding of the complex host-microbiome interactions in rainbow trout and may have implications for the use of probiotics in aquaculture. IMPORTANCE Probiotics are kinds of beneficial live microbes that impart beneficial effects on the host. Recent studies have proven that when given supplementation with probiotics, farmed fish showed improved disease prevention and growth promotion. However, the underlying metabolic functions regarding their involvement in regulating growth phenotypes, nutrient utilization, and immune response are not yet well understood in the aquaculture field. Given the active interactions between the gut microbiota and fish immune and growth performance, we conducted the supplementation experiments with the probiotics Bacillus velezensis and Lactobacillus sakei. The results showed that probiotics mediated intestinal microbiome- and microbiota-derived metabolites regulating the growth and immunity of fish, and different probiotics participated in the species-specific physiological regulation of the host. This study contributed to a better understanding of the functional interactions associated with host health and gut microbiota species.

Molecular mechanisms of the virulence and efficacy of a highly virulent Vibrio anguillarum strain and its formalin-inactivated vaccine in rainbow trout.

In this study, we have isolated four strains of Vibrio anguillarum, revealing that they share the same serotype of O1, biochemical characteristics and virulence factor genes. However, there were differences in haemolytic activity among the bacterial strains; a strain with lower pathogenicity showed γ-haemolytic activity, whereas other virulent strains showed α-haemolytic activity on blood agar and higher empA gene expression in RTG-2 cell line. The most virulent strain was V. anguillarum RTBHR from diseased masu salmon (Oncorhynchus masou), which resulted in mortality of 100% and 93.3% when injected intraperitoneally at concentrations of 9 × 105 and 6.3 × 105 colony-forming units/fish in rainbow trout (Oncorhynchus mykiss) and Coho salmon (Oncorhynchus kisutch), respectively. A formalin-inactivated vaccine of V. anguillarum RTBHR induced a protective and specific immunity in rainbow trout as the vaccinated fish exhibited low cumulative mortality in a challenge test and a high specific antibody response in enzyme-linked immunosorbent assay at 8 weeks post-vaccination. The produced antibody was bound to bacterial proteins of 30-37 kDa in size. This adaptive immune response was detected as early as day 1, with quantitative polymerase chain reaction analysis revealing the upregulated expression of genes encoding for TCRα, T-bet, mIgM and sIgM in rainbow trout. This suggested that the vaccine inducedT (probably a more dominant Th1 response) and B cell responses. In conclusion, the vaccine successfully protected fish from V. anguillarum infection by eliciting cellular and humoral immune responses.

An inactivated vaccine against infectious pancreatic necrosis virus in rainbow trout (Oncorhynchus mykiss)

Infectious pancreatic necrosis virus (IPNV), belonging to the genus Aquabirnavirus within the family Birnaviridae, causes huge economic loss to the global salmonid industry every year. Recently, outbreaks of disease caused by genogroup I IPNV were found in many rainbow trout (Oncorhynchus mykiss) farms worldwide. An inactivated vaccine was prepared using a genogroup I IPNV isolate with an optimized procedure as incubation with β-propanolactone (BPL) at the final concentration of 0.5% at room temperature for 48 h. The inactivated vaccine was used to immunize rainbow trout, and the protection efficiency was evaluated by viral loads determination, immune-related genes quantification, and neutralizing antibody tests. The viral loads in immunized rainbow trout were significantly decreased and the strongest antiviral effect was observed on 30 days post-immunization (d.p.i). The expression of innate immune-related genes IFN-1, and Mx-1 genes were significantly up-regulated on 3, 7, and 15 d.p.i (p < 0.05), and adaptive immune-related genes CD4, CD8, and IgM genes were significantly up-regulated on 15 and 30 d.p.i (p < 0.05). Neutralizing antibodies were firstly detected on 30 d.p.i and the highest titer was observed on 45 d.p.i, which began to decrease on 60 d.p.i, but was still significantly higher than that in negative control fish. The results indicated that the vaccine prepared in this study could stimulate the non-specific and specific immune response and provide significant immune protection to the vaccinated rainbow trout.

The Synergistic Effects of Combined Use of Mentha longifolia, Thymus carmanicus, and Trachyspermum copticum on Growth Performance, Feed Utilization, and Expression of Key Immune Genes in Rainbow Trout (Oncorhynchus mykiss).

Medicinal plants exhibit remarkable positive effects on different aspects of fish physiology. This study aimed to evaluate the possible impact of a combination of plants (Mentha longifolia, Thymus carmanicus, and Trachyspermum copticum) on growth performance, immune responses and key immune gene expression of rainbow trout. For this purpose, four diets were designed, including zero, 0.25, 0.5, and 1% of a mixture of plants per kg of diet, representing dietary treatments of control, T1, T2, and T3, respectively. Two hundred forty fish (weighing 23.11 ± 0.57 g) were fed 3% of body weight twice a day for 45 days. The results showed that growth parameters of weight gain (except for T1) and FCR were significantly improved in fish receiving all levels of plants, with T3 showing the best growth results. Digestive enzymes activities were notably increased in T1 and T2 compared to the control. Stress biomarkers (glucose and cortisol) were significantly decreased in T1 and T2, while T3 was not significantly different from the control. Immunological responses were significantly improved in T2, while T1 andT3 did not show a statistical difference in terms of lysozyme activity. Catalase activity was noticeably decreased in T1, although superoxide dismutase and malondialdehyde were highest in T2. Immune-related genes were significantly up-regulated in T3 compared to other treatments. Also, antioxidant enzyme coding genes were strongly up-regulated in T2 and T3. Overall, the present results suggest that 1% inclusion of the mixture of M. longifolia, T. carmanicus, and T. copticum (T2) can be used to improve the growth and immunity of rainbow trout.

Growth performance, blood biochemistry profile, and immune response of rainbow trout (Oncorhynchus mykiss) fed dietary Persian shallot (Allium stipitatum) powder

Persian shallot is a member of the Alliaceae family and is known for its efficacy as antibacterial and immunostimulant effects, but its application in aquaculture is scarce. Herein, we evaluated the effects of Persian shallot powder (PSP) on the growth performance, blood biochemistry profile, and immune response of rainbow trout. Fish fed dietary PSP at 0, 0.5, 1, and 2% for 56 days, then the growth, serum, and skin mucus indices were evaluated. The final weight, weight gain, and specific growth rate (SGR) were meaningfully enhanced in fish fed 1 and 2%. The voluntary feed intake and protein efficiency ratio were meaningfully higher, while the feed conversion ratio (FCR) was lower in rainbow trout-fed dietary PSP at 1% than the control. The regression analysis illustrated that the optimum dose of PSP powder according to the FCR and SGR results is 1.27–1.35% for rainbow trout. The protease, amylase, and lipase activities were meaningfully increased in rainbow trout-fed PSP powder in a dose-dependent manner. The blood glucose was significantly reduced in fish fed 1 and 2% of PSP than the control. Further, the lactate dehydrogenase was markedly decreased by dietary PSP regardless of the dose. The total serum protein, lysozyme activity, total immunoglobulin (Ig), and complement component C4 were markedly higher in rainbow trout-fed PSP at 1 and 2% than the control. Additionally, the serum complement component C3 is higher in rainbow trout fed 1% PSP than the other groups. The skin mucus total protein level was significantly higher in fish fed PSP at varying levels than the control, and fish fed 1% PSP levels had higher Ig than fish fed 0.5 and 2% levels. The lysozyme and protease activities in the skin mucus samples were higher in fish fed 1 and 2% levels than fish fed 0 and 0.5% levels. The skin mucus Ig is higher in rainbow trout fed 1% PSP than fish fed 0 and 0.5% without difference with 2%. Overall, we recommend the dietary administration of PSP to bolster the performance and immunity of rainbow trout.

Effect of jujube (Ziziphus jujuba) extract on intestinal flora, digestion, and immunity of rainbow trout (Oncorhynchus mykiss)

Jujube (Ziziphus jujuba), as an edible-medicinal fruit, is an important Chinese herbal medicine, which has several beneficial effects on host such as immunomodulation, antioxidant, and gastrointestinal protection. In the study, the beneficial effects of dietary jujube extract supplementation on digestion, nonspecific immunity and intestinal microbial diversity of rainbow trout (Oncorhynchus mykiss) were investigated. The fish were fed for 56 days with diets containing 0 (control), 0.25%, 0.50% and 1.00% jujube extract, and then gastrointestinal digestive enzyme activities, nonspecific immune genes expressions and intestinal microbial diversity were measured. Intestinal protease and α-amylase activities in 0.25% and 0.50% groups, and lactase activity in 0.50% group were significantly improved. The expression of Cu/Zn-superoxide dismutase (SOD) gene was significantly increased in 0.50% and 1.00% groups. Catalase (CAT) and glutathione S-transferase A (GSTA) were significantly increased in 0.50% and 0.25% groups, respectively, while glutathione peroxidase 1 (GPX1) in 0.50% group, complement 3 (C3) in 1.00% group and transforming growth factor-β (TGF-β) in jujube extract groups were all significantly down-regulated. In the gut microflora, there were significant differences in the gut abundances of three phyla (Bacteroidetes, Tenerictes, and Actinobacteria) and eight genera (Dinghuibacter, Lachnospiraceae_ NK4A136_group, Aeromonas, Pseudarthrobacter, Acetatifactor, uncultured_ bacterium mycobacteriumand Rikenellaceae_RC9) among the four experiment groups. Moreover, the abundances of Aeromonas in 0.25% and 0.50% groups were significantly decreased compared with the control group, while Acetatifactor in 0.25% group and Dinghuibacter in 1.00% group were significantly increased. The clusters of orthologous groups of proteins (COG) functional prediction analysis indicated that these differences of intestinal microflora were mainly in metabolism, cellular processes and signaling, and information storage and processing. These results showed that jujube extract can improve the digestive and immune ability, and induce a positive effect on the intestinal flora of rainbow trout.

Dietary effects of a low-molecular weight fraction (

Aquaculture by-products have been of great interest for producing protein hydrolysates with multiple biological activities. The present experiment was carried out to evaluate dietary effects of a low-molecular fraction (<10 kDa) from shrimp waste hydrolysate in forms of unprotected and nanocapsulated on growth and immunity of rainbow trout. Therefore, six diets were designed including a control diet (no supplementation), D1 (1 g kg−1 of unprotected fraction), D2 (1 g kg−1 chitosan nanocapsules), D3 (1 g kg−1 liposome nanocapsules), D4 (1 g kg−1 of fraction-loaded chitosan nanocapsules), D5 (1 g kg−1 of fraction-loaded liposome nanocapsules). Fish (0.91 ± 0.15 g) were fed with experimental diets until apparent satiation for six weeks followed by a 5-day experimental challenge with Streptococcus iniae. Results revealed that growth is strongly affected in fish receiving the fraction with D4 treatment showing the highest weight gain, SGR, final weight and the lowest FCR (p < 0.05). Nanocapsules without fraction did not show remarkable effects when compared to control group. In terms of serum and mucus immune parameters of lysozyme, complement activity, myeloperoxidase activity, and total protease, fish from D4 group showed the highest measured values followed by D5 (p < 0.05). Key immune related genes of IL-6 and TNF-α were noticeably up-regulated in fish from D1, D4, and D5 groups, which were consistent with survival rate after 5 days challenge with Streptococcus iniae. All together, the present findings highlighted the application of chitosan and liposome nanocarriers in aquaculture and potential of low-molecular weight fraction (<10 kDa) from shrimp wastes hydrolysate to improve growth performance and immune status of rainbow trout.

Effects of black mustard (Brassica nigra) seed oil on growth performance, digestive enzyme activities and immune responses in rainbow trout (Oncorhynchus mykiss)

In the present study, effects of black mustard seed oil administration on growth performance, digestive enzyme activities and immune response in rainbow trout (Oncorhynchus mykiss) were evaluated. Rainbow trout were fed with three different doses of black mustard seed oil at the rate of 0.5% (BM0.5), 1% (BM1) and 2% (BM2) along with a control with no supplementation (0%) for 60 days. On 30th and 60th day of the study, digestive enzyme activities and immune responses were examined. At the end of the feeding trial, growth performance and survival against Aeromonas hydrophila infection were also recorded. Growth was positively affected in BM2 fish group, but it was not significantly different. Amylase and lipase levels were not altered compared with control at any sampling time. However, trypsin was increased in all experiential fish groups compared with control (p < 0.05). Pepsin level increased in BM2 fish group only on 60th day of the study (p < 0.05). Respiratory burst activity was significantly decreased in BM2 fish group at both the sampling times compared with control (p < 0.05). Potential killing activity was elevated in BM2 fish group on 30th day (p < 0.05). Lysozyme activity was enhanced in BM1 and BM2 fish groups on 30th day and BM0.5 and BM1 groups on 60th day compared with that of the control (p < 0.05). MPO increased significantly in BM1 and BM2 fish group on 30th day and in all experimental fish groups on 60th day of the study compared with that of the control. No changes in histology of different organs of fish groups were observed. The pro-inflammatory cytokine, IL-1β gene expression in intestine of all treated fish groups was significantly upregulated on 30th day. Similarly, transcription of IL-8 and IL-6, IL-10 and IL-12 cytokine genes was enhanced in intestine cells on 30th day. Similar enhanced levels of these genes were observed in head kidney cells of BM0.5 and BM1 fish groups. Survival against A. hydrophila infection increased insignificantly in all BM-treated groups. All these results indicated that supplementation of BM could elevate intestinal immunity in rainbow trout, and the dietary incorporation of BM at 1%–2% level for 30 days is encouraged.

Dietary methionine as a strategy to improve innate immunity in rainbow trout (Oncorhynchus mykiss) juveniles

Methionine ability to enhance fish immune status and inflammatory response by the modulation of methionine-related pathways has been verified in several fish species. However, no attention has been given to the role of methionine as an immune-modulatory additive in rainbow trout (Oncorhynchus mykiss). Hence, this study was designed to evaluate the effect of short-term feeding a diet supplemented with dl-methionine on the rainbow trout immune status. For this purpose, two diets were formulated: a control (CTRL) diet including the AA profile required to meet the ideal pattern estimated for rainbow trout; and an experimental diet (MET) identical to the CTRL but supplemented with dl-methionine two fold above its requirement level. After 2 and 4 weeks, fish haematological profile, peripheral cell populations, plasma and skin mucus humoral immune parameters as well as head-kidney gene expression were analysed. Results showed that methionine was able to improve peripheral neutrophil numbers after 4 weeks of feeding while reducing the expression of pro-inflammatory genes (i.e. IL1β and IL8). Also, indications of fish physiological ability to regulate polyamine biosynthesis were found by the reduced expression of the spermine synthase enzyme (SMS). Together, these results point to some level of enhancement of the cellular-related innate immune status by dietary dl-methionine supplementation after a short-term feeding period, which could be used as a prophylactic strategy for rainbow trout health management.

Prolactin peptide (pPRL) induces anti-prolactin antibodies, ROS and cortisol but suppresses specific immune responses in rainbow trout

Prolactin has several immune functions in fish however, the effects on innate and specific components of rainbow trout immunity are currently unknown. Therefore in this study, prolactin peptide (pPRL) injection in rainbow trout generated anti-PRL antibodies that were confirmed through Western blot assays of fish brain tissue extract. At the same time, this group of fish was immunized with a viral antigen (VP2) and the specific antibody titer generated by the rainbow trout was subsequently determined, as well as the sero-neutralizing capacity of the antibodies. Interestingly, this group of fish (pPRL-VP2) generated approximately 150% less antibodies compared with fish immunized only with the viral antigen (VP2), and pPRL-VP2 fish increased their cortisol level by 4 times compared to the control. Additionally, through qPCR assay, we determined that the pPRL-VP2 fish group decreased pro-inflammatory transcript expression, and the serum of these (pPRL-VP2) fish stimulated ROS production in untreated fish leukocytes, a phenomenon that was blocked by the pharmacological cortisol receptor inhibitor (RU486). Collectively, this is the first report that indicates that pPRL could modulate both components of immunity in rainbow trout.

Dietary supplementation of garden thyme essential oil ameliorated the deteriorative effects of aflatoxin B1 on growth performance and intestinal inflammatory status of rainbow trout (Oncorhynchus mykiss)

Phytogenics additives have gained considerable attention as efficacious and safe dietary interventions to reduce the toxic effects of aflatoxin B1 contamination in aquatic animals. The present study was conducted to investigate the ameliorative efficacy of Thymus vulgaris essential oil on aflatoxin B1 (AFB1) toxicity in rainbow trout (Oncorhynchus mykiss) in terms of growth performance, innate plasma immune indices and expression of immune related genes. Five experimental diets including a commercial diet as control, control diet +25 ppb AFB1, control diet +50 ppb AFB1, control diet +25 ppb AFB1 + 1% garden thymus essential oil (TEO), and control diet +50 ppb AFB1+ 1% TEO were tested. Triplicate groups of fish averaging 20.77 ± 0.08 g were fed the test diets at a rate of 3% body weight twice daily for 30 days. At the end of the experiment, fish fed TEO supplemented diets showed improved final weight, weight gain, feed conversion ratio and specific growth rates in comparison to groups received AFB1 with no dietary TEO supplementation (P < 0.05). The biochemical (total protein) and innate immune (lysozyme and ACH50) parameters were significantly enhanced in all TEO supplemented groups (P < 0.05). Expression of tumor necrosis factor-alpha, transforming growth factor-β and interleukin-8 were markedly up-regulated following feeding on diet containing high level of AFB1 (P < 0.05). Meanwhile, dietary TEO supplementation ameliorated the increased tumor necrosis factor alpha, transforming growth factor-β and interleukin-8 expression induced by dietary AFB1 contamination (P < 0.05). However, TEO supplementation significantly enhanced interleukin-1β expression (P < 0.05). It can be concluded that, dietary supplementation of 1% TEO can mitigate the AFB1 induced suppression of growth and innate immunity in rainbow trout.

GHRH-SST-GH-IGF axis regulates crosstalk between growth and immunity in rainbow trout (Oncorhynchus mykiss) infected with Vibrio anguillarum

An energy trade-off is existed between immunological competence and growth. The axis of growth hormone releasing hormone, somatostatin, growth hormone, insulin-like growth factor (GHRH-SST-GH-IGF axis) regulates growth performances and immune competences in rainbow trout (Oncorhynchus mykiss). The salmonid-specific whole genome duplication event is known to result in duplicated copies of several key genes in GHRH-SST-GH-IGF axis. In this study, we evaluated the physiological functions of GHRH-SST-GH-IGF axis in regulating crosstalk between growth and immunity. Based on principal components analysis (PCA), we observed the overall expression profiles of GHRH-SST-GH-IGF axis were significantly altered by Vibrio anguillarum infection. Trout challenged with Vibrio anguillarum showed down-regulated igf1s subtypes and up-regulated igfbp1a1. The brain sst genes (sst1a, sst1b, sst3b and sst5) and igfpbs genes (igfbp4s and igfbp5b2) were significantly affected by V. anguillarum infection, while the igfbp4s, igfbp5s, igfbp6s and igf2bps genes showed significant changes in peripheral immune tissues in response to V. anguillarum infection. Gene enrichment analyses showed functional and signaling pathways associated with apoptosis (such as p53, HIF-1 or FoxO signaling) were activated. We further proposed a possible model that describes the IGF and IGFBPs-regulated interaction between cell growth and programmed death. Our study provided new insights into the physiological functions and potentially regulatory mechanisms of the GHRH-SST-GH-IGF axis, indicating the pleiotropic effects of GHRH-SST-GH-IGF axis in regulating crosstalk between growth and immunity in trout.

STAT3/SOCS3 axis contributes to the outcome of salmonid whirling disease.

There are differences in disease susceptibility to whirling disease (WD) among strains of rainbow trout. The North American strain Trout Lodge (TL) is highly susceptible, whereas the German Hofer (HO) strain is more resistant. The suppressor of cytokine signaling (SOCS) proteins are key in inhibiting cytokine signaling. Their role in modulating the immune response against whirling disease is not completely clear. This study aimed at investigating the transcriptional response of SOCS1 and SOCS3 genes to Myxobolus cerebralis along with that of several upstream regulators and immune response genes. M. cerebralis induced the expression of SOCS1, the IL-6-dependent SOCS3, the anti-inflammatory cytokine IL-10 and the Treg associated transcription factor FOXP3 in TL fish at multiple time points, which likely caused a restricted STAT1 and STAT3 activity affecting the Th17/Treg17 balance. The expression of SOCS1 and the IL-6-dependent SOCS3 was induced constraining the activation of STAT1 and STAT3 in TL fish, thereby causing Th17/Treg17 imbalance and leaving the fish unable to establish a protective immune response against M. cerebralis or control inflammatory reactions increasing susceptibility to WD. Conversely, in HO fish, the expression of SOCS1 and SOCS3 was restrained, whereas the expression of STAT1 and IL-23-mediated STAT3 was induced potentially enabling more controlled immune responses, accelerating parasite clearance and elevating resistance. The induced expression of STAT1 and IL-23-mediated STAT3 likely maintained a successful Th17/Treg17 balance and enabled fish to promote effective immune responses favouring resistance against WD. The results provide insights into the role of SOCS1 and SOCS3 in regulating the activation and magnitude of host immunity in rainbow trout, which may help us understand the mechanisms that underlie the variation in resistance to WD.

The effect of Lavandula officinalis nanoemulsion on growth performance, body composition, haematology and immunity parameters of Oncorhynchus mykiss

ABSTRACT Effects of lavender essential oil nanoemulsion (LEON) on the growth, body composition, haematology and immunity of Oncorhynchus mykiss was investigated. A total of 276 healthy fishes were distributed into 12 cages to four treatments in triplicate. The fishe were fed a diet consisting of 0, 100, 150 and 200 ml/kg of LEON for 60 days. Results showed that WG% and SGR (%/day) significantly were increased at the different levels of LEON (p < .05). The highest of WG (%) and SGR were found in 150 ml/kg of LEON (252.16%) followed by 100 and 200 ml/kg. In contrast, FCR was decreased with increasing of dietary supplemental of LEON. The haematology parameters such as RBC, haemoglobin , haematocrit and MCH were significantly increased in 200 ml/kg of LEON compared to the control. ACH50, SOD, lysozyme activity, IgM and total Ig were significantly higher in 200 ml/kg of LEON treatment compared to the control (p < .05). LEON treatments also had a significant influence on body composition like protein and lipid content. Overall, our results interestingly demonstrated that the effect of supplemental dietary LEON especially at the level of 150 and 200 ml/kg had a positive and significant effect on some growth and immunity of rainbow trout.

Dietary probiotic Pediococcus acidilactici MA18/5M modulates the intestinal microbiota and stimulates intestinal immunity in rainbow trout (Oncorhynchus mykiss)

AbstractA study was conducted to evaluate the probiotic effect of Pediococcus acidilactici MA18/5M on rainbow trout, Oncorhynchus mykiss. Fish (310 ± 9 g) were fed a control diet or a P. acidilactici‐supplemented diet (at 2.4 × 106 CFU/g) for 4 weeks. The probiotic was observed to populate the intestine with levels ranging from log 3.7 to 5.4 CFU/g. Furthermore, these populations were able to persist for at least 24 hr after the cessation of probiotic feeding. High‐throughput sequencing analysis of bacterial 16S rRNA libraries demonstrated that P. acidilactici was able to modulate the gut microbiome of rainbow trout and that the probiotic was detected as a common taxon on the mucosa and in the digesta of the probiotic fish (p &lt; .05). Real‐time polymerase chain reaction demonstrated that feeding the probiotic upregulated pro‐inflammatory cytokines, interleukin‐1β, and interleukin‐8 and downregulated anti‐inflammatory interleukin‐10 compared to the control‐fed fish. Furthermore, the mRNA levels for the mucosal antibody immunoglobulin T was also elevated in probiotic‐fed fish. These findings help to explain some of the mechanisms behind the previously reported observed benefits of using this probiotic in the intestinal morphology and immunity of rainbow trout.