Effects of a dietary β-(1,3)(1,6)-D-glucan supplementation on intestinal microbial communities and intestinal ultrastructure of mirror carp (Cyprinus carpio L.)

High-fat diet alters intestinal microbiota and induces endoplasmic reticulum stress via the activation of apoptosis and inflammation in blunt snout bream

The primary organ for absorbing dietary fat is the gut. High dietary lipid intake negatively affects health and absorption by causing fat deposition in the intestine. This research explores the effect of a high-fat diet (HFD) on intestinal microbiota and its connections with endoplasmic reticulum stress and inflammation. 60 fish (average weight: 45.84 ± 0.07 g) were randomly fed a control diet (6% fat) and a high-fat diet (12 % fat) in four replicates for 12 weeks. From the result, hepatosomatic index (HSI), Visceralsomatic index (VSI), abdominal fat (ADF), Intestosomatic index (ISI), mesenteric fat (MFI), Triglycerides (TG), total cholesterol (TC), non-esterified fatty acid (NEFA) content were substantially greater on HFD compared to the control diet. Moreover, fish provided the HFD significantly obtained lower superoxide dismutase (SOD) and glutathione peroxidase (GPX) activities. In contrast, an opposite result was seen in malondialdehyde (MDA) content in comparison to the control. HFD significantly altered intestinal microbiota in blunt snout bream, characterized by an increased abundance of Aeromonas, Plesiomonas proteobacteria, and firmicutes with a reduced abundance of Cetobacterium and ZOR0006. The transcriptional levels of glucose-regulated protein 78 (grp78), inositol requiring enzyme 1 (ire1), spliced X box-binding protein 1 (xbp1), DnaJ heat shock protein family (Hsp40) member B9 (dnajb9), tumor necrosis factor alpha (tnf-α), nuclear factor-kappa B (nf-κb), monocyte chemoattractant protein-1 (mcp-1), and interleukin-6 (il-6) in the intestine were markedly upregulated in fish fed HFD than the control group. Also, the outcome was similar in bax, caspases-3, and caspases-9, ZO-1, Occludin-1, and Occludin-2 expressions. In conclusion, HFD could alter microbiota and facilitate chronic inflammatory signals via activating endoplasmic reticulum stress.

An Evaluation of Laminarin Additive in the Diets of Juvenile Largemouth Bass (Micropterus salmoides): Growth, Antioxidant Capacity, Immune Response and Intestinal Microbiota

A 28 day feeding trial was conducted to investigate the growth performance, immune response and intestinal microbiota of laminarin (LAM) supplemented diets in juvenile largemouth bass (Micropterus salmoides). Four hundred and eighty fish (initial average weight: 0.72 ± 0.04 g) were randomly divided into four groups (40 fish per tank with three replicates in each group) Four diets were prepared with LAM supplementation at the doses of 0 (control), 5 g Kg^-1 (LL), 10 g Kg^-1 (ML) and 15 g Kg^-1 (HL), respectively. No significant difference in the specific growth rate (SGR) and hepatosomatic index (HSI) was observed in fish among the four groups, or in the lipid and ash content of fish flesh. In addition, fish in the LL group exhibited much higher antioxidant capacity (p < 0.05), while the diets with the inclusion of 5 and 10 g Kg^-1 LAM remarkably decreased the antioxidant capacity of fish (p > 0.05). Dietary LAM at the dose of 5 g Kg^-1 inhibited the transcription of interleukin-1β (il-1β) and tumor necrosis factor-α (tnf-α), while promoting the expression of transforming growth factor-β (tgf-β) in fish intestine. Moreover, the beneficial intestinal bacteria Bacteroide, Comamonas and Mycoplasma abundance significantly increased in fish from the LL group, while the content of opportunistic pathogens Plesiomonas, Aeromonas and Brevinema in fish of the HL group was substantially higher than the control group. Overall, the appropriate dose of supplemented LAM in the diet was 5 g Kg^-1, while an excessive supplementation of LAM in the diet led to microbial community instability in largemouth bass.

Effects of Bee Pollen on Growth Performance, Intestinal Microbiota and Histomorphometry in African Catfish

This study aimed to determine the dietary effects of honeybee pollen (BP) on growth parameters, intestinal microbiota, hepatic histoarchitecture, and intestinal histomorphometry of African catfish Clarias gariepinus juveniles. The feeding experiment was carried out in a recirculating aquaculture system under controlled conditions for 21 days to achieve more than a 10-fold increase in weight in fish from the control group. Fish were fed well-balanced commercial feed without any supplements and served as a reference group (group C) and other diets enriched with varying BP levels as 1% (BP1), 2% (BP2), and 3% (BP3). Results showed a significant (p < 0.05) effect of the dietary BP not only on the growth parameters (such as final body weight: 5.0 g to 6.6−7.5 g, weight gain: 0.23 g/d to 0.31−0.35 g/d, body length: 84.7 mm to 93.8−95.9 mm, and specific growth rate: 11.7%/d to 13.1−13.7%/d, group C vs. experimental groups, respectively) but also on the development of beneficially important gut microbiota, such as lactic acid-producing bacteria. In BP-enriched groups, an average of 45% higher body weight gain was observed compared to those reared in the control group. The histological analysis showed that dietary BP may have a positive effect on the development of the intestinal tract and may enhance the absorption of nutrients with the potential ability to maintain a normal hepatic histoarchitecture of the treated African catfish. The results obtained suggest the optimum level of BP additive to feed for African catfish should be 1%.

Modulation of gut microbiota, blood metabolites, and disease resistance by dietary β-glucan in rainbow trout (Oncorhynchus mykiss)

BACKGROUND

Prebiotics are known to have a positive impact on fish health and growth rate, and β-glucans are among the most used prebiotics on the market. In this study, rainbow trout (Oncorhynchus mykiss) were treated with a β-1,3;1,6-glucan dietary supplement (at a dose of 0 g, 1 g, 10 g, and 50 g β-glucan per kg of feed). After 6 weeks, the effect of the β-glucan was evaluated by determining the changes in the microbiota and the blood serum metabolites in the fish. The impact of β-glucan on the immune system was evaluated through a challenge experiment with the bacterial fish pathogen Yersinia ruckeri.

RESULTS

The microbiota showed a significant change in terms of composition following β-glucan treatment, notably an increase in the relative abundance of members of the genus Aurantimicrobium, associated with a decreased abundance of the genera Carnobacterium and Deefgea. Furthermore, analysis of more than 200 metabolites revealed that the relative levels of 53 metabolites, in particular compounds related to phosphatidylcholines, were up- or downregulated in response to the dietary supplementation, this included the amino acid alanine that was significantly upregulated in the fish that had received the highest dose of β-glucan. Meanwhile, no strong effect could be detected on the resistance of the fish to the bacterial infection.

CONCLUSIONS

The present study illustrates the ability of β-glucans to modify the gut microbiota of fish, resulting in alteration of the metabolome and affecting fish health through the lipidome of rainbow trout.

β-Glucan-Induced Immuno-Modulation: A Role for the Intestinal Microbiota and Short-Chain Fatty Acids in Common Carp

Dietary supplementation of fish with β-glucans has been commonly associated with immunomodulation and generally accepted as beneficial for fish health. However, to date the exact mechanisms of immunomodulation by β-glucan supplementation in fish have remained elusive. In mammals, a clear relation between high-fibre diets, such as those including β-glucans, and diet-induced immunomodulation via intestinal microbiota and associated metabolites has been observed. In this study, first we describe by 16S rRNA sequencing the active naive microbiota of common carp intestine. Based on the abundance of the genus Bacteroides, well known for their capacity to degrade and ferment carbohydrates, we hypothesize that common carp intestinal microbiota could ferment dietary β-glucans. Indeed, two different β-glucan preparations (curdlan and MacroGard^®) were both fermented in vitro, albeit with distinct fermentation dynamics and distinct production of short-chain fatty acids (SCFA). Second, we describe the potential immunomodulatory effects of the three dominant SCFAs (acetate, butyrate, and propionate) on head kidney leukocytes, showing effects on both nitric oxide production and expression of several cytokines (il-1b, il-6, tnfα, and il-10) in vitro. Interestingly, we also observed a regulation of expression of several gpr40L genes, which were recently described as putative SCFA receptors. Third, we describe how a single in vivo oral gavage of carp with MacroGard^® modulated simultaneously, the expression of several pro-inflammatory genes (il-1b, il-6, tnfα), type I IFN-associated genes (tlr3.1, mx3), and three specific gpr40L genes. The in vivo observations provide indirect support to our in vitro data and the possible role of SCFAs in β-glucan-induced immunomodulation. We discuss how β-glucan-induced immunomodulatory effects can be explained, at least in part, by fermentation of MacroGard^® by specific bacteria, part of the naive microbiota of common carp intestine, and how a subsequent production of SFCAs could possibly explain immunomodulation by β-glucan via SCFA receptors present on leukocytes.

Hot water extract of Pleurotus pulmonarius stalk waste enhances innate immune response and immune-related gene expression in red hybrid tilapia Oreochromis sp. following challenge with pathogen-associated molecular patterns

In aquaculture, commercial fish such as red hybrid tilapia are usually raised at high density to boost the production within a short period of time. This overcrowded environment, however, may cause stress to the cultured fish and increase susceptibility to infectious diseases. Antibiotics and chemotherapeutics are used by fish farmers to overcome these challenges, but this may increase the production cost. Studies have reported on the potential of mushroom polysaccharides that can act as immunostimulants to enhance the immune response and disease resistance in fish. In the current study, hot water extract (HWE) from mushroom stalk waste (MSW) was used to formulate fish feed and hence administered to red hybrid tilapia to observe the activation of immune system. Upon 30 days of feeding, the fish were challenged with pathogen-associated molecular patterns (PAMPs) such as lipopolysaccharides (LPS) and polyinosinic:polycytidylic acid (poly (I:C)) to mimic bacterial and viral infection, respectively. HWE supplementation promoted better feed utilisation in red hybrid tilapia although it did not increase the body weight gain and specific growth rate compared to the control diet. The innate immunological parameters such as phagocytic activity and respiratory burst activity were significantly higher in HWE-supplemented group than that of the control group following PAMPs challenges. HWE-supplemented diet also resulted in higher mRNA transcription of il1b and tnfa in midgut, spleen and head kidney at 1-day post PAMPs injection. Tlr3 exhibited the highest upregulation in the HWE fed fish injected with poly (I:C). At 3-days post PAMPs injection, both ighm and tcrb expression were upregulated significantly in the spleen and head kidney. Results showed that HWE supplementation enhances the immune responses of red hybrid tilapia and induced a higher serum bactericidal activity against S. agalactiae.

Yarrowia lipolytica N6-glucan protects goat leukocytes against Escherichia coli by enhancing phagocytosis and immune signaling pathway genes

Immunostimulant and protective effects of Yarrowia lipolytica glucans against important pathogens, such as Escherichia coli, have not been investigated in goats and other ruminants. This study aimed to characterize Y. lipolytica N6-glucan (Yl-glucan) and its possible role in immunological signaling pathway activation and immunoprotection against E. coli in goat leukocytes. Characterization analyses showed that Y. lipolytica content had a mix of β and α-D-glucans, molecular weight of 3301.53 kDa and low solubility after the heat treatment. The stimulation of goat leukocytes with Yl-glucan induced protection against E. coli challenge. Remarkably, Yl-glucan and E. coli interaction increased gene expression of dectin-1 and TLR-2 receptors, signaling pathway Syk/NFκB, and cytokines, such as TNF-α and IL-10. As a consequence of signaling activation, phagocytosis, and nitric oxide production enhanced killing of pathogens. Altogether, Y. lipolytica-glucan demonstrated to possess an immunoprotective potential against E. coli through innate immune response modulation in goat leukocytes.

Recovery from Hypersaline-Stress-Induced Immunity Damage and Intestinal-Microbiota Changes through Dietary β-glucan Supplementation in Nile tilapia (Oreochromis niloticus)

Simple Summary

Long-term hypersaline stress can induce coagulation disorders and splenomegaly and down-regulate the complement pathway in tilapia, which can increase risk in healthy breeding. As a prebiotic, β-glucan dietary supplementation can significantly reduce enlarged spleen resulting from hypersaline stress. The hematological aspects of the red blood cell count, hematocrit, red cell distribution width, platelet count, and plateletcrit were also decreased by supplementation with dietary β-glucan. In the spleen and intestine, β-glucan intake significantly decreased the high expression of immune-related genes due to hypersaline stress resulting from β-glucan intake in tilapia. β-glucan supplementation also significantly increased the abundance of beneficial microbiota such as Lactobacillus, Phycicoccus, and Rikenellaceae in the intestine. In summary, β-glucan intake can relieve tissue damage and optimize the intestinal microbiota of tilapia in brackish water and improve fish health.

Abstract

Long-term exposure to hyperosmotic environments can induce severe immune damage and increase risk in tilapia breeding. As an effective immunoregulator, β-glucan has attracted extensive attention in nutritional research and given rise to high expectations of improving health status and alleviating organismal damage in tilapia, Oreochromis niloticus, in brackish water. In this study, an 8-week cultivation experiment was conducted on tilapia fed a basal diet or diets with β-glucan supplementation in freshwater (control) and brackish water. Growth performance, hematological aspects, immune cytokine expression, and the intestinal microbiota of tilapia were analyzed. The results indicated that supplementation with β-glucan significantly reduced the enlarged spleen of tilapia resulting from hypersaline stress. Tilapia fed β-glucan showed significantly-greater decreases in the red blood cell count, hematocrit, red cell distribution width, platelet count, and plateletcrit than those fed the basal diet. β-glucan significantly decreased the high expression of immune-related genes in the spleen induced by hyperosmotic stress. In the intestine, the high migration inhibitory factor-2 (MIF-2) and IL-1β gene expression induced by hypersaline stress was significantly reduced. β-glucan supplementation also significantly increased the abundance of beneficial microbiota such as Lactobacillus, Phycicoccus, and Rikenellaceae. Therefore, dietary β-glucan supplementation can significantly reduce spleen enlargement and improve immune function in tilapia in brackish water. β-glucan intake can also optimize the intestinal microbiota of tilapia in brackish water and improve fish health.

Development of Fish Immunity and the Role of β-Glucan in Immune Responses

Administration of β-glucans through various routes, including immersion, dietary inclusion, or injection, have been found to stimulate various facets of immune responses, such as resistance to infections and resistance to environmental stress. β-Glucans used as an immunomodulatory food supplement have been found beneficial in eliciting immunity in commercial aquaculture. Despite extensive research involving more than 3000 published studies, knowledge of the receptors involved in recognition of β-glucans, their downstream signaling, and overall mechanisms of action is still lacking. The aim of this review is to summarize and discuss what is currently known about of the use of β-glucans in fish.

Effect of β-1/3,1/6-glucan upon immune responses and bacteria in the gut of healthy common carp (Cyprinus carpio)

β-glucans are frequently included in the diet of healthy common carp Cyprinus carpio as a pre-emptive measure for combatting disease. In order to study the effect this has on the relationship between the gut bacteria and host immune response, carp were maintained on either a β-glucan free diet or feed containing 0.1% MacroGard®, a β-1/3, 1/6-glucan, for up to 7 weeks and analysis of innate immune gene expression and molecular analysis of the gut bacteria was performed. The data reveals feeding of MacroGard® to healthy carp does not induce bactericidal innate immune gene expression in the gut but does appear to alter bacterial species richness that did not have a negative effect on overall health. Analysis of innate immune gene expression within the upper midgut revealed that there were significant changes over time in the expression of Interleukin (il)-1β, inducible nitric oxide synthase (inos), mucin (muc2) and C-reactive protein (crp2). Diet did not affect the number of copies of the bacterial 16s rDNA gene in the gut, used as a as a measure of total bacteria population size. However, PCR-denaturing gradient gel electrophoresis (DGGE) analysis revealed a shift in bacterial species richness with MacroGard feeding. Bactericidal immune gene expression of crp2, muc2 and il-1β was weakly correlated with gut bacteria population size indicating a potentially limited role of these genes in interacting with the gut bacteria in healthy carp in order to maintain gut homeostatic conditions. These findings highlight the importance of considering both host immunity and the microbiome together in order to fully elucidate the effeect of immunomodulants, such as β-glucans, upon gut health.

Yeast β-glucans and microalgal extracts modulate the immune response and gut microbiome in Senegalese sole (Solea senegalensis)

One bottleneck to sustainability of fish aquaculture is the control of infectious diseases. Current trends include the preventive application of immunostimulants and prebiotics such as polysaccharides. The present study investigated how yeast β-glucan (Y), microalgal polysaccharide-enriched extracts (MAe) and whole Phaeodactylum tricornutum cells (MA) modulated the gut microbiome and stimulated the immune system in Senegalese sole (Solea senegalensis) when administered by oral intubation. Blood, intestine and spleen samples were taken at 3 h, 24 h, 48 h and 7 days after treatment. The short-term response (within 48 h after treatment) consisted of up-regulation of il1b and irf7 expression in the gut of the Y treated group. In contrast, administration of MAe decreased expression of tnfa and the chemokine cxc10 in the gut and spleen. Both treatments down-regulated the expression of irf3 with respect to the control group. Lysozyme activity in plasma decreased at 48 h only in the MAe-treated soles. Medium-term response consisted of the up-regulation of clec and irf7 expression in the gut of the Y, MAe and MA groups and of il1b mRNAs in the spleen of the MA group compared to the control group. Microbiome analysis using 16S rDNA gene sequencing indicated that the intestine microbiome was dominated by bacteria of the Vibrio genus (>95%). All the treatments decreased the relative proportion of Vibrio in the microbiome and Y and MAe decreased and MA increased diversity. Quantitative PCR confirmed the load of bacteria of the Vibrio genus was significantly decreased and this was most pronounced in Y treated fish. These data indicate that orally administrated insoluble yeast β-glucans acted locally in the gut modulating the immune response and controlling the Vibrio abundance. In contrast, the MAe slightly reduced the Vibrio load in the intestine and caused a transient systemic anti-inflammatory response. The results indicate that these polysaccharides are a promising source of prebiotics for the sole aquaculture industry.

Haematological and intestinal health parameters of rainbow trout are influenced by dietary live yeast and increased water temperature

Live yeast may be a sustainable protein source in salmonid diets while exhibiting a probiotic effect to counteract environmental stressors, such as increased water temperature that is being exacerbated by climate change. The objective of this study was to evaluate the effects of feeding a high dietary inclusion of live yeast and increased water temperature on growth, haematological and intestinal physiology of rainbow trout. For six weeks, 129 g fish in 16 tanks (n = 4) were fed either a diet based on fishmeal or based on live yeast (214 g kg^-1 of diet or 7.6 log CFU g^-1 of Saccharomyces cerevisiae) that replaced 40% of fishmeal protein while fish were reared in water temperatures of either 11 °C (cold) or 18 °C (warm). Fish weights, caudal blood and proximal and distal intestines were collected and analysed. Fish fed live yeast resulted in reduced growth (SGR and WG) and higher FCR, while growth in cold and warm water was similar despite differences in TGC. However, increased mortality, plasma cortisol, and intestinal oedema and villous damage indicated fish reared in warm water were subjected to chronic stress. Temperature had a significant effect on haematocrit and red blood cell counts that resulted in significantly higher haemoglobin levels in fish kept in warm water attributed to an elevated oxygen demand. In the proximal intestine, increased temperature resulted in reduced expression of pro-inflammatory cytokines, e.g. TNFα and IL8, that were further reduced in fish fed live yeast. In addition, feeding live yeast reduced gene expression of CLD6 involved in gut barrier function, which suggests that the level of yeast was too high and masked any beneficial effects on fish health. In conclusion, feeding a high inclusion of live yeast reduced fish growth and expression of intestinal genes, while increasing the temperature from 11 to 18 °C subjected fish to chronic stress that restricted growth, suppressed innate immunity and induced intestinal damage. Replacing 40% of fishmeal protein with live yeast did not counteract negative effects caused by increased temperature, thus alternative strategies need to be explored and implemented to protect the growth and health of rainbow trout from seasonal and long-term rises in water temperature.

Different β-glucans improve the growth performance and bacterial resistance in Nile tilapia

The role of glucan as a biologically active immunomodulator has been well documented for more than 40 years. However, the wide diversity of β-glucan forms and the extraction process has implications for the benefits of these compounds. Biorigin developed two samples of β-glucans using different biotechnological processes. Thus, in the present study, we fed Nile tilapia (Oreochromis niloticus) diets containing these two β-glucan molecules (BG01 and BG02) for 30 days prior to bacterial infection with Streptococcus agalactiae. The results showed that the different β-glucan samples exhibited biologically differently behaviors, but both increased the resistance against bacterial infection. Specifically, BG01 increased immunostimulation, while BG02 improved growth performance. In summary, these findings confirm the benefits of β-glucans in aquaculture and also provide further evidence of the growth promotion of these compounds.

Dietary β-glucans differentially modulate immune and stress-related gene expression in lymphoid organs from healthy and Aeromonas hydrophila-infected rainbow trout (Oncorhynchus mykiss)

Although β-glucans stimulating effects have already been demonstrated on the immune system of numerous animal species, available data remain relatively variable and more research should be done regarding the complexity of underlying mechanisms. In this context, the present study aimed to evaluate the stress and immune-related effects of dietary β-glucans (i.e. Macrogard^®) by considering a number of influencing factors such as the dose (0, 0.1, 0.2 and 0.5% in food), feeding duration (15 versus 30 days), tissue (blood, kidney, spleen, gills) and infection status (healthy or infected). Blood parameters (lysozyme, ACH50 activities, leucocyte populations) and mRNA expression level of several immune- and stress-related genes (TFN-α1, IL-1β, IL10, COX-2, TGF-β, MC2R, HSP70) were measured. Our results suggest that spleen may be a highly responsive organ to dietary β-glucans both in healthy or infected fish, and that this organ may therefore significantly contribute to the immune reinforcement induced by such immunostimulatory diet. Our study further reveals that overdoses of β-glucans and/or prolonged medication can lead to a non-reactive physiological status and, consequently, to a poor immune response. All in all, the current data emphasizes the need for further extensive research in the field of dietary β-glucans as a preventive method for farmed fish protection.

Long-lived effects of administering β-glucans: Indications for trained immunity in fish

Over the past decades, it has become evident that immune-modulation of fish with β-glucans, using injection, dietary or even immersion routes of administration, has stimulating but presumed short-lived effects on both intestinal and systemic immunity and can increase protection against a subsequent pathogenic challenge. Although the exact effects can be variable depending on, among others, fish species and administration route, the immune-stimulating effects of β-glucans on the immune system of fish appear to be universal. This review provides a condensed update of the most recent literature describing the effects of β-glucans on the teleost fish immune system. We shortly discuss possible mechanisms influencing immune-stimulation by β-glucans, including microbial composition of the gut, receptor recognition and downstream signalling. Of interest, in mammalian monocytes, β-glucans are potent inducers of trained immunity. First, we screened the literature for indications of this phenomenon in fish. Criteria that we applied include indications for at least one out of three features considered characteristic of trained immunity; (i) providing protection against a secondary infection in a T- and B-lymphocyte independent manner, (ii) conferring increased resistance upon re-infection and, (iii) relying on key roles for innate immune cell types such as natural killer cells and macrophages. We conclude that several indications exist that support the notion that the innate immune system of teleost fish can be trained. Second, we screened the literature for indications of long-lived effects on innate immunity of fish after administering β-glucans, a criterion which could help to identify key roles for macrophages on resistance to infection. We discuss whether β-glucans, as well-known immune-stimulants, are able to train the immune system of fish and argue in favour of further studies designed to specifically investigate this phenomenon in fish.

Dietary β-glucan improved growth performance, Vibrio counts, haematological parameters and stress resistance of pompano fish, Trachinotus ovatus Linnaeus, 1758

This study evaluated effects of graded levels of dietary β-glucan (0, 0.5, 1, 2 and 4 g kg(-1)) on growth performance, haematological parameters, intestinal Vibrio counts, dose requirement and salinity stress resistance in pompano fish Trachinotus ovatus (6.45 g ± 0.06 (SEM)). After 8-weeks of diet feeding, growth was significantly higher in fish fed diets with 0.10% β-glucan compared to fish fed control diet (no β-glucan). Survival increased significantly in fish fed 0.05 and 0.10% β-glucan compared to control diet. There were significant increases in red blood cells (in 0.20% β-glucan diet), in total leukocytes (in 0.05-0.20% β-glucan diet), in both lymphocyte and monocyte count in fish fed 0.10%-0.40% β-glucan diet. However, dietary β-glucan did not affect neutrophil, eosinophil and basophil counts. Intestinal Vibrio counts were reduced in fish fed any level of β-glucan compared to control. In addition, dietary β-glucan levels highly correlated with growth, survival, intestinal Vibrio counts and haematological index. Optimal β-glucan levels for maximal growth of fish were predicted to be 0.122% at day 21 (R(2) = 98.53%), 0.120% at day 28 (R(2) = 78.55%), 0.115% at day 42 (R(2) = 62.21%) and 0.090% at day 56 (R(2) = 75.18%), showing a decreasing β-glucan requirement with increasing fish size. Furthermore, optimal β-glucan levels for maximal haematological parameters based on lymphocyte count, was estimated to be 0.120% (R(2) = 98.53%) at day 56. Also, fish fed 0.05%-0.20% β-glucan showed better resistance against salinity stress. In conclusion, β-glucan supplementation is effective for improving growth, intestinal Vibrio counts and boosted stress resistance of the pompano fish, T. ovatus.

Environmental cues and symbiont microbe-associated molecular patterns function in concert to drive the daily remodelling of the crypt-cell brush border of the Euprymna scolopes light organ

Recent research has shown that the microbiota affects the biology of associated host epithelial tissues, including their circadian rhythms, although few data are available on how such influences shape the microarchitecture of the brush border. The squid-vibrio system exhibits two modifications of the brush border that supports the symbionts: effacement and repolarization. Together these occur on a daily rhythm in adult animals, at the dawn expulsion of symbionts into the environment, and symbiont colonization of the juvenile host induces an increase in microvillar density. Here we sought to define how these processes are related and the roles of both symbiont colonization and environmental cues. Ultrastructural analyses showed that the juvenile-organ brush borders also efface concomitantly with daily dawn-cued expulsion of symbionts. Manipulation of the environmental light cue and juvenile symbiotic state demonstrated that this behaviour requires the light cue, but not colonization. In contrast, symbionts were required for the observed increase in microvillar density that accompanies post dawn brush-border repolarization; this increase was induced solely by host exposure to phosphorylated lipid A of symbiont cells. These data demonstrate that a partnering of environmental and symbiont cues shapes the brush border and that microbe-associated molecular patterns play a role in the regulation of brush-border microarchitecture.

Dietary β-glucan (MacroGard®) enhances survival of first feeding turbot (Scophthalmus maximus) larvae by altering immunity, metabolism and microbiota

Reflecting the natural biology of mass spawning fish aquaculture production of fish larvae is often hampered by high and unpredictable mortality rates. The present study aimed to enhance larval performance and immunity via the oral administration of an immunomodulator, β-glucan (MacroGard(®)) in turbot (Scophthalmus maximus). Rotifers (Brachionus plicatilis) were incubated with or without yeast β-1,3/1,6-glucan in form of MacroGard(®) at a concentration of 0.5 g/L. Rotifers were fed to first feeding turbot larvae once a day. From day 13 dph onwards all tanks were additionally fed untreated Artemia sp. nauplii (1 nauplius ml/L). Daily mortality was monitored and larvae were sampled at 11 and 24 dph for expression of 30 genes, microbiota analysis, trypsin activity and size measurements. Along with the feeding of β-glucan daily mortality was significantly reduced by ca. 15% and an alteration of the larval microbiota was observed. At 11 dph gene expression of trypsin and chymotrypsin was elevated in the MacroGard(®) fed fish, which resulted in heightened tryptic enzyme activity. No effect on genes encoding antioxidative proteins was observed, whilst the immune response was clearly modulated by β-glucan. At 11 dph complement component c3 was elevated whilst cytokines, antimicrobial peptides, toll like receptor 3 and heat shock protein 70 were not affected. At the later time point (24 dph) an anti-inflammatory effect in form of a down-regulation of hsp 70, tnf-α and il-1β was observed. We conclude that the administration of MacroGard(®) induced an immunomodulatory response and could be used as an effective measure to increase survival in rearing of turbot.

Intestinal microbiota and immune related genes in sea cucumber (Apostichopus japonicus) response to dietary β-glucan supplementation

β-glucan is a prebiotic well known for its beneficial outcomes on sea cucumber health through modifying the host intestinal microbiota. High-throughput sequencing techniques provide an opportunity for the identification and characterization of microbes. In this study, we investigated the intestinal microbial community composition, interaction among species, and intestinal immune genes in sea cucumber fed with diet supplemented with or without β-glucan supplementation. The results show that the intestinal dominant classes in the control group are Flavobacteriia, Gammaproteobacteria, and Alphaproteobacteria, whereas Alphaproteobacteria, Flavobacteriia, and Verrucomicrobiae are enriched in the β-glucan group. Dietary β-glucan supplementation promoted the proliferation of the family Rhodobacteraceae of the Alphaproteobacteria class and the family Verrucomicrobiaceae of the Verrucomicrobiae class and reduced the relative abundance of the family Flavobacteriaceae of Flavobacteria class. The ecological network analysis suggests that dietary β-glucan supplementation can alter the network interactions among different microbial functional groups by changing the microbial community composition and topological roles of the OTUs in the ecological network. Dietary β-glucan supplementation has a positive impact on immune responses of the intestine of sea cucumber by activating NF-κB signaling pathway, probably through modulating the balance of intestinal microbiota.

Teleost microbiomes: the state of the art in their characterization, manipulation and importance in aquaculture and fisheries

Indigenous microbiota play a critical role in the lives of their vertebrate hosts. In human and mouse models it is increasingly clear that innate and adaptive immunity develop in close concert with the commensal microbiome. Furthermore, several aspects of digestion and nutrient metabolism are governed by intestinal microbiota. Research on teleosts has responded relatively slowly to the introduction of massively parallel sequencing procedures in microbiomics. Nonetheless, progress has been made in biotic and gnotobiotic zebrafish models, defining a core microbiome and describing its role in development. However, microbiome research in other teleost species, especially those important from an aquaculture perspective, has been relatively slow. In this review, we examine progress in teleost microbiome research to date. We discuss teleost microbiomes in health and disease, microbiome ontogeny, prospects for successful microbiome manipulation (especially in an aquaculture setting) and attempt to identify important future research themes. We predict an explosion in research in this sector in line with the increasing global demand for fish protein, and the need to find sustainable approaches to improve aquaculture yield. The reduced cost and increasing ease of next generation sequencing technologies provides the technological backing, and the next 10 years will be an exciting time for teleost microbiome research.