A Microbial Feed Additive Abates Intestinal Inflammation in Atlantic Salmon

Inhibition of TNBS-induced intestinal inflammation in crucian carp (Carassius carassius) by oral administration of bioactive Bioactive food derived peptides

Intestinal enteritis is a main issue in crucian carp production which results in massive economic loss. Traditional antibiotics used for disease prevention of crucian carp (Carassius carassius) have been banned, thus an alternative approach needs to be identified. In this study, the bioactive peptide was evaluated as a diet supplement for preventing intestinal inflammation in crucian carp. Intestinal inflammation was induced by intrarectal administration of a 2,4,6-trinitrobenzene sulfonic acid (TNBS) solution. The fish samples were fed with different diets for 14 days. The disease activity index (DAI), which included, fish swimming, food intake, anal inflammation, body surface, and ascites was determined daily. Intestine segments were stained with haematoxylin and eosin (H.E.) for histopathological analysis. The expression of cytokines, including interleukin-1β (IL-1β), interleukin-8 (IL-8), tumor necrosis factor α (TNF-α), and myeloperoxidase (MPO) in crucian carp were determined. In TNBS-induced groups, the DAI scores were dramatically increased compared to the control group. The histopathological analysis showed that the damage of the fish intestine after the injection of TNBS. The relative expression levels of pro-inflammation cytokines (TNF-α, IL-1β, IL-8, MPO) were significantly increased compared to the control group on day 1. In the TNBS-induced group feed with a diet supplemented with bioactive peptide, the symptoms of intestinal inflammation were relieved on day 3 and the mRNA expression levels of pro-inflammation cytokines (TNF-α, IL-1β, IL-8, MPO) were reduced compared to day 1. On day 7, the fish samples enrofloxacin group and bioactive peptide group were recovered from TNBS-induced intestinal inflammation. This study showed that the fish diet supplemented with bioactive peptide could help to prevent and recover from intestinal inflammation. Thus, the bioactive peptide can be used as a replacement for antibiotics to prevent disease in aquaculture production.

Alleviating effects of essential oil from Artemisia vulgaris on enteritis in zebrafish via modulating oxidative stress and inflammatory response

Artemisia vulgaris (A. vulgaris) is a traditional Chinese medicine widely distributed in China and contains many bioactive compounds with pharmacological effects. However, the anti-inflammatory effects and mechanism of essential oil from A. vulgaris on enteritis in fish are still unclear. In this study, in order to elucidate the underlying mechanism of essential oil from A. vulgaris on zebrafish enteritis, zebrafish were used for establishing animal models to observe the histopathological changes of intestines, determine the activities of immune-related enzymes and oxidative stress indicators, and the mRNA expression of genes in MyD88/TRAF6/NF-KB signaling pathways. The results showed that different doses of A. vulgaris essential oil could effectively alleviate zebrafish enteritis in a dose- and time-dependent manner by improving the intestinal histopathological damage, decreasing the intestinal oxidative stress, repairing the intestinal immune ability, changing the expression levels of IL-1β, IL-10 and genes in MyD88/TRAF6/NF-κB pathway. In addition, co-treatment with oxazolone and MyD88 inhibitor could alleviate the morphological damage, the induction of oxidative stress, and the levels of immune-related enzymes and the mRNA expression of genes in MyD88/TRAF6/NF-κB signaling pathway. Moreover, essential oil from A. vulgaris had more significantly therapeutic effects on enteritis of male zebrafish than that of female zebrafish. This result will clarify the therapeutic effect and anti-inflammatory mechanism of essential oil from A. vulgaris on zebrafish enteritis, and provide a theoretical basis for further research on the rationality of A. vulgaris to replace feed antibiotics.

In silico, in vitro and in vivo characterization of host-associated Latilactobacillus curvatus strains for potential probiotic applications in farmed Atlantic salmon (Salmo salar)

Salmon aquaculture is the fastest growing animal protein production system in the world; however, intensive farming leads to poor weight gain, stress, and disease outbreaks. Probiotics offer the potential to enhance growth performance and feed efficiency in Atlantic salmon, as well as immunostimulate fish against common pathogens, benefitting farmers and consumers with more efficient production. Here, we isolated and identified 900 native microbial isolates including 18 Lactobacilli from the farmed salmon intestines. Based on whole-genome sequencing and phylogenetic analysis, the Lactobacillus candidates belonged to Latilactobacillus curvatus (L. curvatus) species and formed two distinct phylogenetic groups. Using bioinformatics and in vitro analyses, we selected two candidates L. curvatus ATCC PTA-127116 and L. curvatus ATCC PTA-127117, which showed desirable safety and probiotic properties. The two L. curvatus candidates were evaluated for safety and efficacy (higher final weight) in Atlantic salmon alongside spore-forming Bacilli isolated from salmon, poultry, and swine. All the tested candidates were safe to salmon with no adverse effects. While we did not see efficacy in any Bacillus supplemented groups, compared to untreated group, the group administered with the two L. curvatus strains consortium in feed for seven weeks in freshwater showed indicators of improvement in final body weight by 4.2%. Similarly, the two L. curvatus candidates were also evaluated for safety and efficacy in Atlantic salmon in saltwater; the group administered with the two L. curvatus strains consortium in feed for 11 weeks showed indicators of improvement in final body weight by 4.7%. Comprehensive metabolomics analyses in the presence of different prebiotics and/or additives identified galactooligosaccharide as a potential prebiotic to enhance the efficacy of two L. curvatus candidates. All together, these data provide comprehensive genomic, phenotypic and metabolomic evidence of safety and desirable probiotic properties as well as indicators of in vivo efficacy of two novel endogenous L. curvatus candidates for potential probiotic applications in Atlantic salmon. The in vivo findings need to be confirmed in larger performance studies, including field trials.

Use of Probiotic Bacteria and Bacteriocins as an Alternative to Antibiotics in Aquaculture

In addition to their use in human medicine, antimicrobials are also used in food animals and aquaculture, and their use can be categorized as therapeutic against bacterial infections. The use of antimicrobials in aquaculture may involve a broad environmental application that affects a wide variety of bacteria, promoting the spread of bacterial resistance genes. Probiotics and bacteriocins, antimicrobial peptides produced by some types of lactic acid bacteria (LAB), have been successfully tested in aquatic animals as alternatives to control bacterial infections. Supplementation might have beneficial impacts on the intestinal microbiota, immune response, development, and/or weight gain, without the issues associated with antibiotic use. Thus, probiotics and bacteriocins represent feasible alternatives to antibiotics. Here, we provide an update with respect to the relevance of aquaculture in the animal protein production sector, as well as the present and future challenges generated by outbreaks and antimicrobial resistance, while highlighting the potential role of probiotics and bacteriocins to address these challenges. In addition, we conducted data analysis using a simple linear regression model to determine whether a linear relationship exists between probiotic dose added to feed and three variables of interest selected, including specific growth rate, feed conversion ratio, and lysozyme activity.

Single and Multi-Strain Probiotics Supplementation in Commercially Prominent Finfish Aquaculture: Review of the Current Knowledge

The Nile tilapia Oreochromis niloticus, Atlantic salmon Salmo salar, rainbow trout Oncorhynchus mykiss, olive flounder Paralichthys olivaceus, common carp Cyprinus carpio, grass carp Ctenopharyngodon idella and rohu carp Labeo rohita are farmed commercially worldwide. Production of these important finfishes is rapidly expanding, and intensive culture practices can lead to stress in fish, often reducing resistance to infectious diseases. Antibiotics and other drugs are routinely used for the treatment of diseases and sometimes applied preventatively to combat microbial pathogens. This strategy is responsible for the emergence and spread of antimicrobial resistance, mass killing of environmental/beneficial bacteria, and residual effects in humans. As an alternative, the administration of probiotics has gained acceptance for disease control in aquaculture. Probiotics have been found to improve growth, feed utilization, immunological status, disease resistance, and to promote transcriptomic profiles and internal microbial balance of host organisms. The present review discusses the effects of single and multi-strain probiotics on growth, immunity, heamato-biochemical parameters, and disease resistance of the above-mentioned finfishes. The application and outcome of probiotics in the field or open pond system, gaps in existing knowledge, and issues worthy of further research are also highlighted.

Fishing for the right probiotic: Host-microbe interactions at the interface of effective aquaculture strategies

Effective aquaculture management strategies are paramount to global food security. Growing demands stimulate the intensification of production and create the need for practices that are both economically viable and environmentally sustainable. Importantly, pathogenic microbes continue to be detrimental to fish growth and survival. In terms of host health, the intestinal mucosa and its associated consortium of microbes have a critical role in modulating fitness and present an attractive opportunity to promote health at this interface. In light of this, the administration of probiotic microorganisms is being considered as a means to restore and sustain health in fish. Current evidence suggests that certain probiotic strains might be able to augment immunity, enhance growth rate, and protect against infection in salmonids, the most economically important family of farmed finfish. This review affirms the relevance of host-microbe interactions in salmonids in light of emerging evidence, with an emphasis on intestinal health. In addition, the current understanding of the mode of action of probiotics in salmonid fish is discussed, along with delivery systems that can effectively carry the living microbes.

Skin damage caused by scale loss modifies the intestine of chronically stressed gilthead sea bream (Sparus aurata, L.)

The present study was designed to test if the damage caused by scale loss provokes a change in other innate immune barriers such as the intestine and how chronic stress affects this response. Sea bream (Sparus aurata) were kept in tanks at low density (16 kg m^-3, LD) or exposed to a chronic high density (45 kg m^-3, HD) stress for 4 weeks. Scales were then removed (approximately 50%) from the left flank in the LD and HD fish. Intestine samples (n = 8/group) were examined before and at 12 h, 3 days and 7 days after scale removal. Changes in the morphology of the intestine revealed that chronic stress and scale loss was associated with intestinal inflammation. Specifically, enterocyte height and the width of the lamina propria, submucosa and muscle layer were significantly increased (p < 0.05) 3 days after skin damage in fish under chronic stress (HD) compared to other treatments (LDWgut3d or HDgut0h). This was associated with a significant up-regulation (p < 0.05) in the intestine of gene transcripts for cell proliferation (pcna) and anti-inflammatory cytokine tgfβ1 and down-regulation of gene transcripts for the pro-inflammatory cytokines tnf-α and il1β (p < 0.05) in HD and LD fish 3 days after scale removal compared to the undamaged control (LDgut0h). Furthermore, a significant up-regulation of kit, a marker of mast cells, in the intestine of HDWgut3d and LDWgut3d fish suggests they may mediate the crosstalk between immune barriers. Skin damage induced an increase in cortisol levels in the anterior intestine in HDWgut12 h fish and significant (p < 0.05) down-regulation of mr expression, irrespective of stress. These results suggest glucocorticoid levels and signalling in the intestine of fish are modified by superficial cutaneous wounds and it likely modulates intestine inflammation.

Dietary Inclusion of Black Soldier Fly (Hermetia Illucens) Larvae Meal and Paste Improved Gut Health but Had Minor Effects on Skin Mucus Proteome and Immune Response in Atlantic Salmon (Salmo Salar)

The present study investigated effects of dietary inclusion of black soldier fly larvae (BSFL) (Hermetia illucens) meal and paste on gut health, plasma biochemical parameters, immune response and skin mucus proteome in pre-smolt Atlantic salmon (Salmo salar). The seven-week experiment consisted of seven experimental diets: a control diet based on fishmeal and plant protein (Control-1); three BSFL meal diets, substituting 6.25% (6.25IM), 12.5% (12.5IM) and 25% (25IM) of protein; two BSFL paste diets, substituting 3.7% (3.7IP) and 6.7% (6.7IP) of protein and an extra control diet with 0.88% of formic acid (Control-2). The 6.25IM diet reduced enterocyte steatosis in pyloric caeca, improved distal intestine histology, and reduced IgM in distal intestine. The fish fed 12.5IM diet reduced enterocyte steatosis in pyloric caeca, improved distal intestine histology, had a higher plasma lysozyme content compared to 6.25IM, and tend to increase phagocytic activity in head-kidney macrophages-like cells. On the other hand, 25IM diet improved distal intestine histology, but showed mild-moderate enterocyte steatosis in pyloric caeca, increased IFNγ and reduced IgM in distal intestine. In the case of BSFL paste diets, 3.7IP diet caused mild inflammatory changes in distal intestine, although it reduced enterocyte steatosis in pyloric caeca. The 6.7IP diet reduced enterocyte steatosis in pyloric caeca and improved distal intestine histology. Increasing level of BSFL meal in the diet linearly decreased plasma C-reactive protein, whereas increasing level of BSFL paste linearly increased plasma antioxidant capacity. Dietary inclusion of BSFL meal and paste had minor effects on the expression profile of proteins in skin mucus and no effects on immune markers in splenocytes. BSFL meal showed no negative effect on liver and muscle health as indicated by plasma alanine aminotranseferase, asparate aminotransferase and creatine kinase. The present study showed that replacing conventional protein sources with low to moderate levels of BSFL meal (6.25% and 12.5%) or paste (3.7% and 6.7%) reduced enterocyte steatosis in pyloric caeca, while replacing up to 25% with BSFL meal or 6.7% with paste improved distal intestine histology. Further, dietary inclusion of BSFL meal and paste had minor effects on skin mucus proteome and immune response in Atlantic salmon.

Nutrient Digestibility, Growth, Mucosal Barrier Status, and Activity of Leucocytes From Head Kidney of Atlantic Salmon Fed Marine- or Plant-Derived Protein and Lipid Sources

Nutrient digestibility, growth, and mucosal barrier status of fish skin, gills, and distal intestine were studied in Atlantic salmon fed feeds based on marine or plant-derived ingredients. The barrier status was assessed by considering the expression of four mucin genes, five genes that encode antimicrobial proteins, distal intestine micromorphology, and design-based stereology of the midgut epithelium. In addition, the head kidney leukocytes were examined using flow cytometry; to understand the differences in their counts and function. Five experimental feeds containing the main components i) fishmeal and fish oil (BG1), ii) soybean meal (BG2; to induce enteritis), iii) fishmeal as the main protein source and rapeseed oil as the main lipid source (BG3), iv) a mix of plant protein concentrates as the protein sources and fish oil as the lipid source (BG4), and v) plant and marine ingredients in the ratio 70:30 (BG5) were produced for the study. Atlantic salmon with initial weight 72.7 ± 1.2 g was offered the experimental feeds for 65 days. The results revealed that the weights of all fish groups doubled, except for fish fed BG2. Fish fed the BG2 diet had lower blood cholesterol concentration, developed enteritis, had lower expression of muc2 in the distal intestine, and had a compromised barrier status in the intestine. Expression of both the mucin genes and genes that encode antimicrobial peptides were tissue-specific and some were significantly affected by diet. The fish fed BG1 and BG3 had more head kidney lymphocyte-like cells compared to BG5-fed fish, and the phagocytic activity of macrophage-like cells from the head kidney was the highest in fish fed BG1. The intestinal micromorphology and the mucosal mapping suggest two different ways by which plant-based diets can alter the gut barrier status; by either reducing the mucous cell sizes, volumetric densities and barrier status (as noted for BG2) or increasing volumetric density of mucous cells (as observed for BG4 and BG5). The results of the compromised intestinal barrier in fish fed plant ingredients should be further confirmed through transcriptomic and immunohistochemical studies to refine ingredient composition for sustainable and acceptable healthy diets.

Intestinal Transcriptome Analysis Reveals Soy Derivative-Linked Changes in Atlantic Salmon

Intestinal inflammation in farmed fish is a non-infectious disease that deserves attention because it is a major issue linked to carnivorous fishes. The current norm is to formulate feeds based on plant-derived substances, and the ingredients that have antinutritional factors are known to cause intestinal inflammation in fishes such as Atlantic salmon. Hence, we studied inflammatory responses in the distal intestine of Atlantic salmon that received a feed rich in soybean derivatives, employing histology, transcriptomic and flow cytometry techniques. The fish fed on soy products had altered intestinal morphology as well as upregulated inflammation-associated genes and aberrated ion transport-linked genes. The enriched pathways for the upregulated genes were among others taurine and hypotaurine metabolism, drug metabolism-cytochrome P450 and steroid biosynthesis. The enriched gene ontology terms belonged to transmembrane transporter- and channel-activities. Furthermore, soybean products altered the immune cell counts; lymphocyte-like cell populations were significantly higher in the whole blood of fish fed soy products than those of control fish. Interestingly, the transcriptome of the head kidney did not reveal any differential gene expression, unlike the observations in the distal intestine. The present study demonstrated that soybean derivatives could evoke marked changes in intestinal transport mechanisms and metabolic pathways, and these responses are likely to have a significant impact on the intestine of Atlantic salmon. Hence, soybean-induced enteritis in Atlantic salmon is an ideal model to investigate the inflammatory responses at the cellular and molecular levels.

Anatomy, immunology, digestive physiology and microbiota of the salmonid intestine: Knowns and unknowns under the impact of an expanding industrialized production

Increased industrialized production of salmonids challenges aspects concerning available feed resources and animal welfare. The immune system plays a key component in this respect. Novel feed ingredients may trigger unwarranted immune responses again affecting the well-being of the fish. Here we review our current knowledge concerning salmon intestinal anatomy, immunity, digestive physiology and microbiota in the context of industrialized feeding regimes. We point out knowledge gaps and indicate promising novel technologies to improve salmonid intestinal health.

Salmonid Antibacterial Immunity: An Aquaculture Perspective

The aquaculture industry is continuously threatened by infectious diseases, including those of bacterial origin. Regardless of the disease burden, aquaculture is already the main method for producing fish protein, having displaced capture fisheries. One attractive sector within this industry is the culture of salmonids, which are (a) uniquely under pressure due to overfishing and (b) the most valuable finfish per unit of weight. There are still knowledge gaps in the understanding of fish immunity, leading to vaccines that are not as effective as in terrestrial species, thus a common method to combat bacterial disease outbreaks is the use of antibiotics. Though effective, this method increases both the prevalence and risk of generating antibiotic-resistant bacteria. To facilitate vaccine design and/or alternative treatment efforts, a deeper understanding of the teleost immune system is essential. This review highlights the current state of teleost antibacterial immunity in the context of salmonid aquaculture. Additionally, the success of current techniques/methods used to combat bacterial diseases in salmonid aquaculture will be addressed. Filling the immunology knowledge gaps highlighted here will assist in reducing aquaculture losses in the future.

The Application of Single-Cell Ingredients in Aquaculture Feeds—A Review

Single-cell ingredients (SCI) are a relatively broad class of materials that encompasses bacterial, fungal (yeast), microalgal-derived products or the combination of all three microbial groups into microbial bioflocs and aggregates. In this review we focus on those dried and processed single-cell organisms used as potential ingredients for aqua-feeds where the microorganisms are considered non-viable and are used primarily to provide protein, lipids or specific nutritional components. Among the SCI, there is a generalised dichotomy in terms of their use as either single-cell protein (SCP) resources or single-cell oil (SCO) resources, with SCO products being those oleaginous products containing 200 g/kg or more of lipids, whereas those products considered as SCP resources tend to contain more than 300 g/kg of protein (on a dry basis). Both SCP and SCO are now widely being used as protein/amino acid sources, omega-3 sources and sources of bioactive molecules in the diets of several species, with the current range of both these ingredient groups being considerable and growing. However, the different array of products becoming available in the market, how they are produced and processed has also resulted in different nutritional qualities in those products. In assessing this variation among the products and the application of the various types of SCI, we have taken the approach of evaluating their use against a set of standardised evaluation criteria based around key nutritional response parameters and how these criteria have been applied against salmonids, shrimp, tilapia and marine fish species.

Screening of Host Specific Lactic Acid Bacteria Active Against Escherichia coli From Massive Sample Pools With a Combination of in vitro and ex vivo Methods

A novel three-step combination of in vitro and ex vivo screening was established to massively screen host derived lactic acid bacteria (LAB) from the broiler chicken intestine with inhibitory activity against Escherichia coli. In a first step, a massive sample pool consisting of 7102 broiler-derived colonies from intestinal contents were established and sub-cultured. Supernatants thereof were incubated with an E. coli model strain to screen suitable isolates with inhibitory activity. A total of 76 isolates of interest were subsequently further studied based on either pH dependent or -independent activity in the second step of the assay. Here, in-depth growth inhibition of the E. coli model strain and the potential of isolates for lactic acid production as inhibitory substance were indexed for all isolates. Resulting scatter plots of both parameters revealed five isolates with exceptional inhibitory activity that were further studied under ex vivo condition in the third step of the assay. These isolates were taxonomically classified as strains of the species Lactobacillus agilis, Lactobacillus salivarius, and Pediococcus acidilactici. Samples from the broiler chicken intestine were inoculated with the Lactobacillus isolates and the E. coli model strain. After 8 and 24 h incubation, respectively, growth of the E. coli model strain was monitored by cultivation of the E. coli strain in antibiotic supplemented medium. By their superior inhibitory activity against the E. coli model strain, one L. agilis and one L. salivarius strain were selected and characterized for further application as probiotics in broiler chicken. Additionally, their antibiotic resistance patterns and resilience under gastric stress of isolates were also characterized. The results of this study demonstrate that the novel isolation procedure was able to efficiently and rapidly isolate and identify bacterial strains from a massive sample pool with inhibitory potential against specific types of bacteria (here E. coli). The introduction of the final ex vivo selection step additionally confirmed the inhibitory activity of the strains under conditions simulating the intestinal tract of the host. Furthermore, this method revealed a general potential for the isolation of antagonistic strains that active against other pathogenic bacteria with specific biomarker.

Influence of Dietary Supplementation of Probiotic Pediococcus acidilactici MA18/5M During the Transition From Freshwater to Seawater on Intestinal Health and Microbiota of Atlantic Salmon (Salmo salar L.)

The aim of this study was to assess the effect of the transfer from freshwater to seawater on the distal intestinal bacterial communities of Atlantic salmon (Salmo salar L.) and to evaluate the effect of dietary inclusion of Pediococcus acidilactici MA18/5M (at 1.19 × 10⁶ CFU/g). In this context, fish health and antiviral response were also investigated. A 12-week feeding trial was conducted in a flow-through rearing system involving 6 weeks in freshwater and 6 weeks in seawater. Fish received a control and probiotic diet. The composition of the salmon gut bacterial communities was determined by high-throughput sequencing of digesta and mucosa samples from both the freshwater and seawater stage. The main phyla detected during both freshwater and seawater stages were Firmicutes, Proteobacteria, Fusobacteria, and Actinobacteria. Significant differences were observed between the intestinal microbiota in the digesta and the mucosa. Both probiotic supplementation and the seawater transfer (SWT) had a substantial impact on the microbial communities, with most pronounced changes detected in the mucosal communities after SWT. This last finding together with a significantly higher antiviral response (mx-1 and tlr3 gene expression) in the distal intestine of fish fed the probiotic diet suggest a causal link between the microbiota modulation and activation of antiviral response. Feeding probiotics during the freshwater stage did not significantly increase survival after infectious pancreatic necrosis virus (IPNV) challenge after SWT, although higher survival was observed in one out of two replicate challenge tanks. In conclusion, this study demonstrated that both dietary probiotic supplementation and transfer from freshwater to seawater have an important role in modulating the bacterial communities in the distal intestine of Atlantic salmon. Furthermore, supplementation of the diet with P. acidilactici MA18/5M can modulate antiviral response.

A New Isolate of Pediococcus pentosaceus (SL001) With Antibacterial Activity Against Fish Pathogens and Potency in Facilitating the Immunity and Growth Performance of Grass Carps

Probiotic-feeding continues to be a promising strategy to control the bacterial pathogens in aquaculture. A new Pediococcus pentosaceus strain (SL001) was isolated from 1000s of soil samples, which exhibited wide antimicrobial spectrum of against fish pathogens, involving Aeromonas hydrophila, Aeromonas veronii, Aeromonas sobria, Edwardsiella tarda, Lactococcus garvieae, and Plesiomonas shigelloide. The challenge test against A. hydrophila showed that the survival rate of SL001-supplemented group was significantly higher than that of control group (P < 0.05). Moreover, SL001 could stably colonize in gut of grass carp and increased mucus-secreting goblet cells and extended intestinal villi could be observed in SL001-supplemented group (P < 0.05). Feeding with SL001 supplemented diet could significantly enhance the growth rate (P < 0.05) and markedly affect gut microbiota structure of grass carps, resulting in reduced potential pathogens and increased potential probiotics. Furthermore, feeding grass carps with SL001 caused the up-regulated expression of insulin-like growth factor (IGF-1 and IGF-2) and down-regulated expression of myostatin (MSTN-1 and MSTN-2) (P < 0.05), which probably also account for the increased growth rate of SL001-fed group. Meanwhile, relative mRNA expression levels of immune-related genes in liver, spleen, and head kidney were analyzed in grass carps after feeding for 30 days with SL001 supplemented diets. In all three immune organs, the expression levels of immunoglobulin M (IgM) and complement 3 (C3) were significantly increased (P < 0.05), whereas the interleukin-8 (IL-8) was down-regulated (P < 0.05). Besides, whole genome sequencing revealed several probiotics properties of SL001, including organic acid synthesis, bacteriocin synthesis (coagulin), superoxide dismutase, and digestive enzymes. In conclusion, P. pentosaceus SL001 which could enhance immunity and promoter growth rate of grass carps, is prospective to be used as a dietary probiotic in freshwater fish aquaculture.

Dietary fatty acid source has little effect on the development of the immune system in the pyloric caeca of Atlantic salmon fry

The quality and relative amounts of dietary lipids may affect the health and growth of cultured Atlantic salmon. So far, little is known about their effects on the performance of the fish immune system during early life stages and, in particular their importance in the transition from endogenous nutrition (yolk) in the alevin stage to exogenous nutrition in the later fry stage. We investigated the immunomodulatory effects of fish oil, vegetable oil and phospholipid-rich oil in feeds for farmed Atlantic salmon using a transcriptomic approach. The experiment allowed a fine-scale monitoring of gene expression profiles in two tissues, the pyloric caeca of the intestine and the liver, in a 94 days-long first feeding experiment. The analysis of transcriptional profiles revealed that first feeding induced a strong immunomodulation in the pyloric caeca after 48 days of feeding, lasting up to day 94 and possibly beyond. On the other hand, the differential effect of the three dietary regimes was negligible. We interpret this upregulation, undetectable in liver, as a potentiation of the immune system upon the first contact of the digestive system with exogenous feed. This process involved a complex network of gene products involved in both cellular and humoral immunity. We identified the classical pathway of the complement system, acting at the crossroads between innate and adaptive immunity, as a key process modulated in response to the switch from endogenous to exogenous nutrition.

Feeding European sea bass (Dicentrarchus labrax) juveniles with a functional synbiotic additive (mannan oligosaccharides and Pediococcus acidilactici): An effective tool to reduce low fishmeal and fish oil gut health effects?

The aim of this study was to assess the effects of dietary mannan oligosaccharides (MOS), Pediococcus acidilactici or their conjunction as a synbiotic in low fish meal (FM) and fish oil (FO) based diets on European sea bass (Dicentrarchus labrax) disease resistance and gut health. For that purpose, sea bass juveniles were fed one of 6 diets containing different combinations of MOS (Biomos^® and Actigen^©; Alltech, Inc., Kentucky, USA) and Pediococcus acidilactici (BAC, Bactocell^®; Lallemand Inc., Cardiff, UK) replacing standard carbohydrates as follows (MOS (%)/BAC (commercial recommendation): high prebiotic level (HP) = 0.6/0, low prebiotic level (LP) = 0.3/0, only probiotic (B) = 0/+, high prebiotic level plus probiotic (HPB) = 0.6/+, low prebiotic level plus probiotic (LPB) = 0.3/+, control (C) = 0/0 for 90 days. After 60 and 90 days of feeding trial, fish were subjected to an experimental infection against Vibrio anguillarum. Additionally, inducible nitric oxide synthase (iNOS) and tumor necrosis factor α (TNFα) gut patterns of immunopositivity and major histocompatibility complex class II (MHCII), transforming growth factor β (TGF-β), regulatory T-cell subset (CD4⁺T lymphocytes) and effector T cell (CD8α⁺T lymphocytes) gene expression patterns in gut by in situ hybridization were evaluated after 90 days of feeding. The effects of both additives on posterior gut through Gut Associated Lymphoid Tissue (GALT) gene expression was also studied. Fish fed the prebiotic and its combination with P. acidilactici presented increased weight regardless of the dose supplemented after 90 days of feeding, however no effect was detected on somatic indexes. For posterior gut, morphometric patterns and goblet cells density was not affected by MOS, P. acidilactici or its combination. Anti-iNOS and anti-TNFα gut immunopositivity patterns were mainly influenced by MOS supplementation and not by its combination with P. acidilactici. MHCII-β, TCR-β, CD4 and CD8-α positive cells distribution and incidence was not affected by diet. Fish fed HP dose presented a clear up-regulation of TNF-α, cyclooxygenase-2 (COX-2), CD4 and IL10, whereas P. acidilactici dietary supplementation increased the number of interleukin-1β (IL1β) and COX-2 gene transcripts. Synbiotic supplementation resulted in a reduction of MOS-induced gut humoral proinflammatory response by increasing the expression of some cellular-immune system related genes. Fish mortality after V. anguillarum infection was reduced in fish fed LPB and LP diets compared to fish fed the non-suppelmented diet after 90 days of feeding. Thus, overall pointing to the combination of a low dose of MOS and P. acidilactici as synbiont (LPB) as a viable tool to potentiate European sea bass juvenile's growth and disease resistance when supplemented in low FM and FO diets.

Fermented Soybean Meal Increases Lactic Acid Bacteria in Gut Microbiota of Atlantic Salmon (Salmo salar)

The main goal of the present study was to address the effect of feeding fermented soybean meal-based diet to Atlantic salmon on gut microbiota. Further, expression of genes of interest, including cathelicidin antimicrobial peptide (cath), mucin 2 (muc2), aquaporin (aqp8ab), and proliferating cell nuclear antigen (pcna), in proximal intestine of fish fed either experimental diet was analyzed. Three experimental diets, including a control fishmeal (30% FM), soybean meal (30% SBM), or fermented soybean meal diet (30% FSBM) were randomly assigned to triplicate tanks during a 50-day trial. The PCR-TTGE showed microbiota composition was influenced by experimental diets. Bands corresponding to genus Lactobacillus and Pediococcus were characteristic in fish fed the FSBM-based diet. On the other hand, bands corresponding to Isoptericola, Cellulomonas, and Clostridium sensu stricto were only observed in fish FM-based diet, while Acinetobacter and Altererythrobacter were detected in fish fed SBM-based diet. The expression of muc2 and aqp8ab were significantly greater in fish fed the FSBM-based diet compared with the control group. Our results suggest feeding FSBM to Atlantic salmon may (1) boost health and growth physiology in fish by promoting intestinal lactic acid bacteria growth, having a prebiotic-like effect, (2) promote proximal intestine health by increasing mucin production, and (3) boost intestinal trans-cellular uptake of water. Further research to better understands the effects of bioactive compounds derived from the fermentation process of plant feedstuff on gut microbiota and the effects on health and growth in fish is required.

Under control: how a dietary additive can restore the gut microbiome and proteomic profile, and improve disease resilience in a marine teleostean fish fed vegetable diets

BACKGROUND

The constant increase of aquaculture production and wealthy seafood consumption has forced the industry to explore alternative and more sustainable raw aquafeed materials, and plant ingredients have been used to replace marine feedstuffs in many farmed fish. The objective of the present study was to assess whether plant-based diets can induce changes in the intestinal mucus proteome, gut autochthonous microbiota and disease susceptibility of fish, and whether these changes could be reversed by the addition of sodium butyrate to the diets. Three different trials were performed using the teleostean gilthead sea bream (Sparus aurata) as model. In a first preliminary short-term trial, fish were fed with the additive (0.8%) supplementing a basal diet with low vegetable inclusion (D1) and then challenged with a bacteria to detect possible effects on survival. In a second trial, fish were fed with diets with greater vegetable inclusion levels (D2, D3) and the long-term effect of sodium butyrate at a lower dose (0.4%) added to D3 (D4 diet) was tested on the intestinal proteome and microbiome. In a third trial, the long-term effectiveness of sodium butyrate (D4) to prevent disease outcome after an intestinal parasite (Enteromyxum leei) challenge was tested.

RESULTS

The results showed that opposed forces were driven by dietary plant ingredients and sodium butyrate supplementation in fish diet. On the one hand, vegetable diets induced high parasite infection levels that provoked drops in growth performance, decreased intestinal microbiota diversity, induced the dominance of the Photobacterium genus, as well as altered the gut mucosal proteome suggesting detrimental effects on intestinal function. On the other hand, butyrate addition slightly decreased cumulative mortality after bacterial challenge, avoided growth retardation in parasitized fish, increased intestinal microbiota diversity with a higher representation of butyrate-producing bacteria and reversed most vegetable diet-induced changes in the gut proteome.

CONCLUSIONS

This integrative work gives insights on the pleiotropic effects of a dietary additive on the restoration of intestinal homeostasis and disease resilience, using a multifaceted approach.

Nannochloropsis oceania-derived defatted meal as an alternative to fishmeal in Atlantic salmon feeds

Defatted microalgal biomass derived from biorefinery can be potential feed ingredients for carnivorous fish. The present study investigated the growth, feed intake:gain and health parameters in Atlantic salmon fed for 84 days with defatted Nannochloropsis oceania as a fishmeal replacer. Fish fed feeds containing the algal biomass (at 10 and 20% inclusion, alga groups) were compared with groups that consumed alga-devoid feeds (control group). The fish that received 20% alga tended to have reduced weight gain and specific growth rate. Condition factor, feed conversion ratio and feed intake of this fish group were significantly different when compared with the control group. Hepatosomatic and viscerosomatic indices, whole body and fillet proximate composition were not affected by the dietary treatments. Digestibility of dry matter, protein, lipid, ash and energy, as well as retention of lipid and energy of the fish that received feed with 20% alga meal were also significantly different from those of the control group. Serum superoxide dismutase activity of the 10% alga-fed fish was significantly higher compared with the control fish. Although alga feeding did not cause any distal intestinal inflammation, the intestinal proteins that were altered upon feeding 20% algal meal might be pointing to systemic physiological disturbances. In conclusion, feeds with 20% alga had a negative effect on feed intake, FCR, lipid and energy retention and health of the fish. The defatted Nannochloropsis oceania can be used at modest inclusion levels, around 10%, without negative effects on the performance of Atlantic salmon.

Dietary Yeast Cell Wall Extract Alters the Proteome of the Skin Mucous Barrier in Atlantic Salmon (Salmo salar): Increased Abundance and Expression of a Calreticulin-Like Protein

In order to improve fish health and reduce use of chemotherapeutants in aquaculture production, the immunomodulatory effect of various nutritional ingredients has been explored. In salmon, there is evidence that functional feeds can reduce the abundance of sea lice. This study aimed to determine if there were consistent changes in the skin mucus proteome that could serve as a biomarker for dietary yeast cell wall extract. The effect of dietary yeast cell wall extract on the skin mucus proteome of Atlantic salmon was examined using two-dimensional gel electrophoresis. Forty-nine spots showed a statistically significant change in their normalised volumes between the control and yeast cell wall diets. Thirteen spots were successfully identified by peptide fragment fingerprinting and LC-MS/MS and these belonged to a variety of functions and pathways. To assess the validity of the results from the proteome approach, the gene expression of a selection of these proteins was studied in skin mRNA from two different independent feeding trials using yeast cell wall extracts. A calreticulin-like protein increased in abundance at both the protein and transcript level in response to dietary yeast cell wall extract. The calreticulin-like protein was identified as a possible biomarker for yeast-derived functional feeds since it showed the most consistent change in expression in both the mucus proteome and skin transcriptome. The discovery of such a biomarker is expected to quicken the pace of research in the application of yeast cell wall extracts.

Recognition of purified beta 1,3/1,6 glucan and molecular signalling in the intestine of Atlantic salmon

Atlantic salmon was orally intubated with a highly purified β-glucan product (MacroGard(®)) to study the recognition of the molecule by the receptor genes, the regulation of the downstream signalling genes and global proteins, and the micromorphological changes in the intestine. The β-glucan receptor genes of Atlantic salmon, sclra, sclrb, sclrc and cr3, seem to recognize the molecule, and initiate the downstream ITAM-motif signalling, as evident from the significantly high mRNA levels of ksyk, mapkin2, il1b and mip2a levels. Among the altered proteins, the Apoa4 (involved in carbohydrate and lipid metabolism); Tagln, Actb (uptake of β-glucan); Psma2 (associated with substrate recognition); and Ckt (energy metabolism-related) were the overexpressed ones. The underexpressed proteins included the Uk114, Rpl9, Ctsb and Lgal that are connected to proliferation, LPS-stimulation, Il1b and lactose recognition, respectively. Furthermore, the mRNA levels of igt and the number of immune cells in the distal intestine were found to increase upon β-glucan uptake by the fish. This study provides some clues on the mechanisms by which the β-glucan evokes response in Atlantic salmon, particularly at the intestinal level.