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Xylooligosaccharides (XOSs) are being explored as prebiotics in fish diets; however, their effects and modes of action have not been well evaluated. Reports have shown that dietary XOS has the potential to improve the proliferation of beneficial gut microbes, and their metabolites, and enhance disease resistance in several fish species. In contrast, other studies report no substantial changes in immune and growth parameters compared to control groups. Like all prebiotics, the mode of action of XOS is based on their selective stimulation of beneficial gut microbiota, which will outcompete and prevent pathogen proliferation in the gut, and produce metabolites that modulate host immune responses. The reports of improved growth performance of XOS fed fish may be due to improved intestinal microbiome, enhanced glycolysis activity and elevated gastrointestinal enzymatic activities. Dietary XOSs have different effects on fish performance depending on the fish species and the structure of XOSs (degree of XOS polymerization and substitution). Nevertheless, further research is essential to determine the optimal dosage, degree of polymerization, and substitution levels required to improve each fish species' gut health and growth performance. This review highlights the prebiotic effects of XOSs, their mechanism of action, and knowledge gaps. [ABSTRACT FROM AUTHOR]

With the rising awareness of antimicrobial resistance, the development and use of functional feed additives (FFAs) as an alternative prophylactic approach to improve animal health and performance is increasing. Although the FFAs from yeasts are widely used in animal and human pharma applications already, the success of future candidates resides in linking their structural functional properties to their efficacy in vivo. Herein, this study aimed to characterise the biochemical and molecular properties of four proprietary yeast cell wall extracts from S. cerevisiae in relation to their potential effect on the intestinal immune responses when given orally. Dietary supplementation of the YCW fractions identified that the α-mannan content was a potent driver of mucus cell and intraepithelial lymphocyte hyperplasia within the intestinal mucosal tissue. Furthermore, the differences in α-mannan and β-1,3-glucans chain lengths of each YCW fraction affected their capacity to be recognised by different PRRs. As a result, this affected the downstream signalling and shaping of the innate cytokine milieu to elicit the preferential mobilisation of effector T-helper cell subsets namely Th17, Th1, Tr1 and FoxP3+-Tregs. Together these findings demonstrate the importance of characterising the molecular and biochemical properties of YCW fractions when assessing and concluding their immune potential. Additionally, this study offers novel perspectives in the development specific YCW fractions derived from S. cerievisae for use in precision animal feeds. [ABSTRACT FROM AUTHOR]

A 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 < .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. [ABSTRACT FROM AUTHOR]

Fish were fed a single‐strain yeast fraction (SsYF; 2 g/kg) or a multistrain yeast fraction (MsYF; 0.8 g/kg) for 10 weeks. The results demonstrated significant (p ≤ 0.03) elevations in weight gain, specific growth rate, protein efficiency ratio, and feed conversion ratio in fish fed the yeast fraction‐supplemented diets. In the distal intestine, a significant elevation in microvilli density was observed after 5 and 10 weeks of dietary supplementation with MsYF and SsYF, respectively, compared to control fed fish (p < 0.001). A significant elevation (p = 0.02) in the perimeter ratio was observed in fish fed diets supplemented with the yeast fractions. After 10 weeks of feeding on the experimental diets, Rt‐qPCR demonstrated a significant downregulation (p < 0.05) in the stress response genes, heat‐shock protein 70 (hsp70) and proliferating cell nuclear antigen (pcna), in fish fed diets supplemented with the yeast fractions. Significant (p < 0.05) elevations in interleukin 1‐beta (il1β) and interleukin‐10 (il10) gene expression were observed in fish fed diets supplemented with the MsYF compared to the other dietary groups. These findings suggest that feeding an MsYF specifically at a lower incorporation rate < 1 g/kg, compared to a commercial SsYF at 2 g/kg, is effective in improving the intestinal health status and growth performance of European seabass. [ABSTRACT FROM AUTHOR]

Previous studies have shown that the gut microbiota of fish differs depending on host feeding habits and these populations may also be influenced by dietary ingredients. In this study, the bacterial populations of the intestinal tract of the opportunistic omnivore jundiá Rhamdia quelen and the typical omnivore tilapia Oreochromis niloticus were investigated in two experiments. In experiment I, the levels of amylolytic, cellulolytic, lipolytic, proteolytic and total culturable bacteria were compared in the proximal, mid and distal intestine using selective agar. Higher levels of amylolytic, cellulolytic, lipolytic, proteolytic and total culturable bacteria were observed in the tilapia than jundiá, in all intestinal regions. Jundiá contained higher levels of proteolytic bacteria and lipid digesting bacteria in the distal intestinal portion as compared with the mid intestine; both fish species also presented more amylolytic bacteria in the distal intestine. In experiment II, the amylolytic intestinal microbiota between the two species was compared after administration of diets containing different carbohydrate sources. Jundiá fed broken rice presented higher total culturable bacterial levels; however, dietary cassava bagasse and ground corn significantly elevated the population of amylolytic bacteria in tilapia ( P > 0.05). PCR- DGGE was also used to assess the bacterial communities in experiment II. A Cetobacterium spp. was detected in jundiá fed diets containing broken rice, and tilapia fed cassava bagasse, dextrin, broken rice and ground corn. Microbial differentiation was further demonstrated between jundiá and tilapia, because an uncultured bacterium was unique in tilapia and an uncultured spirochete was observed only in jundiá; the presence of these bacterial species was also influenced by dietary carbohydrate sources. [ABSTRACT FROM AUTHOR]

Abstract: The effects of dietary applications of a commercial probiotic (Bacillus spp.) and prebiotic (mannan oligosaccharides [MOS]), used singularly and combined (i.e. synbiotic), on larval survival, growth, intestinal microbial communities and stress resistance of larval European lobster, Homarus gammarus, were assessed. Larvae were reared in green water culture for 12days from hatch until metamorphosis to zoea III. Un-supplemented Artemia nauplii (control) or Artemia nauplii enriched with probiotics (Bacillus spp. 100mgl−1), prebiotic (MOS 12mgl−1) or synbiotics (100mgl−1 Bacillus spp.+MOS 12mgl−1) were each fed to 3 replicate groups of zoea I lobsters for 12days. The effects on gut microbiota were assessed using culture-dependent methods at 1, 7 and 12days post-hatch (dph) and PCR-DGGE at 1 and 12dph. PCR-DGGE was also used to assess microbial communities of the live feeds. Carapace length and weight of five H. gammarus from each replicate was recorded on 1, 7, and 12dph and survival to zoea III was recorded. A low salinity stress test was used as a measure of organism fitness at day 12. After 12dph, H. gammarus larvae fed experimental treatments had significantly (P <0.02) improved weight, carapace length and weight gain, compared to larvae fed control treatments. Survival to 12dph was elevated by all treatments and was significantly (P <0.001) increased for the Bacillus and MOS fed larvae. Salinity stress tolerance was greatest in larvae fed Bacillus although all experimental treatments produced enhanced tolerance to salinity stress in comparison to larvae fed control treatment. Culture-dependent analysis of the gut microbiota of larval lobsters demonstrated the colonisation of Bacillus spp. in larvae fed probiotic or synbiotic enriched live feeds. There was also a reduction in Vibrio levels in certain biotic fed larvae and live feed treatments. PCR-DGGE revealed that the number of observed taxonomical units (OTUs), species richness and species diversity increased in zoea III lobsters fed probiotic, prebiotic and synbiotic. Subsequently, the microbial profiles were dissimilar to the control group with the synbiotic group showing the greatest dissimilarity to the control (36.54±2.54%). The similarity between bacterial communities associated with Artemia and zoea III larvae was highest in the Bacillus treatments (53.86%). The present study demonstrates the benefit of applying dietary supplementation of Bacillus, MOS and Bacillus +MOS on the GI microbiota of lobster larvae which subsequently improved growth performance and stress tolerance. [Copyright &y& Elsevier]

The article presents a study on the influence of different feeding schemes on enzyme activities of gut microbiota in Atlantic cod (Gadus morhua L.). It examines enzyme producing bacteria that were isolated from the gastrointestinal (GI) tract and determines the most promising enzyme-producing bacteria through 16S ribosomal RNA (rRNA). It suggests that the diversity of bacteria appears to be influenced by the feeding regimes.

Abstract: Nanoparticles (NPs) can be ingested by organisms, and NPs with antimicrobial properties may disrupt beneficial endogenous microbial communities and affect organism health. Zebrafish were fed diets containing Cu-NPs or Ag-NPs (500 mg kg−1 food), or an appropriate control for 14 d. Intestinal epithelium integrity was examined by transmission electron microscopy, and microbial community structure within the intestine was assessed by denaturing gradient gel electrophoresis (DGGE) of partial 16S rRNA. No lesions were observed in intestinal epithelia; however, presence of NPs in diets changed intestinal microbial community structure. In particular, some beneficial bacterial strains (e.g., Cetobacterium somerae) were suppressed to non-detectable levels by Cu-NP exposure, and two unidentified bacterial clones from the Firmicutes phylum were sensitive (not detected) to Cu, but were present in Ag and control fish. Unique changes in zebrafish microbiome caused by exposure to Ag-NP and Cu-NP indicate that NP ingestion could affect digestive system function and organism health. [Copyright &y& Elsevier]

As no information is available regarding the efficacy of using rice protein concentrate ( RPC) to replace fishmeal ( FM) in diets for European sea bass ( Dicentrarchus labrax), a trial was conducted to determine the optimum inclusion for European sea bass juveniles. Diets were formulated to replace 25%, 50% and 75% of fishmeal with RPC. Additional high level inclusion diets (50% and 75%) were supplemented with lysine and methionine to determine if these were limiting factors. Fish (18.0 ± 0.06 g) were fed the experimental diets for 12 weeks. The final mean weight and specific growth rate ( SGR) were significantly higher in fish fed the control diet (diet FM) and low level RPC (diet RPC25) than in fish fed the other diets. The supplementation of the amino acids had a positive effect on growth, elevating the final weight of the high level RPC ( RPC75 + AA) group above that of the non-supplemented group ( RPC75). However, this was still not comparable to fish fed FM and RPC25 diets. No significant differences in body composition were observed. A digestibility study demonstrated an inverse relationship between elevating inclusion levels of RPC and apparent digestibility coefficients ( ADCs) for dry matter and lipid, with significantly lower values than the control being observed with RPC inclusions above 25%. The mesenteric fat index followed this trend. Circulating leucocyte levels, leucocyte ratios and serum lysozyme activity remained unaffected by dietary treatment. However, compared with the control group, fish fed RPC75, RPC50 + AA RPC75 + AA displayed significantly lower haematocrit values. The present study demonstrates that the inclusion of RPC at 140 g kg−1 (effectively replacing 25% of FM content) does not compromise European sea bass growth performance, body quality or basic haematological parameters. It is suggested that future studies including higher levels test the efficacy of additional amino acid supplementation (e.g. tryptophan). [ABSTRACT FROM AUTHOR]

Abstract: A novel yeast co-product obtained from a bio-ethanol process in which wheat was the predominant feedstock was tested in a series of iso-nitrogenous (38% crude protein) and iso-lipidic (8%) diets for juvenile mirror carp (Cyprinus carpio). The fishmeal protein component of a basal diet (control treatment) was effectively replaced by a yeast protein concentrate (YPC) at 7.5, 15, 20, and 50% of total dietary protein. After an 8week feeding trial all fish fed YPC showed better (P <0.05) growth performance than the control fed fish, with diets containing 15% and 20% YPC being optimal. Proximate composition analysis revealed that body protein, lipid and NFE levels were unaffected by dietary treatment (P >0.05), however, ash levels were elevated in fish fed ≥15% YPC (P <0.05). Subsequently, body gross energy was significantly reduced at 50% YPC inclusion. Both alanine aminotranferase (ALAT) and aspartate aminotranferase (ASAT) were measured as indicators of hepatic function in carp. Liver ASAT activity was significantly lower in fish fed 20% and 50% YPC, but no effects were seen in ALAT activities. Additionally, preliminary histological assessment of liver and intestinal tissues gave no indication of impairment to health, but high YPC inclusion (≥15%) elevated the number of goblet cells present in the posterior intestine (P <0.05). Molecular microbiological analysis using DGGE revealed no distinctive changes in intestinal microbial communities. This study reveals the potential benefits of utilising a biofuel derived YPC on the growth and feed utilisation performance of carp, with no apparent detrimental impacts on general health and physiological status as determined by gut and liver function and related metabolism. [Copyright &y& Elsevier]

The article focuses on the influence of probiotic adhesion to intestinal mucosa on the activity and morphology of rainbow trout enterocytes. Probiotics can adhere to the intestinal mucus and mucosa. Pediococcus acidilactici-like bacteria on the distal intestinal epithelium of rainbow trout post feeding on Pediococcus acidilactici-supplemented diets.

Abstract: A preliminary study was conducted to evaluate the effect of graded dietary supplementation of Sangrovit®, a commercial product containing the isoquinoline alkaloid sanguinarine, on red tilapia (Oreochromis niloticus) growth performance, feed utilisation, hepatic function, haematological parameters and gut microbiota. Compared to the control group (1.03 g fish−1 day−1), significant elevations in mean daily feed intake (1.19–1.25) were observed in fish fed Sangrovit® diets during the 60-day feeding period. Consequently, the specific growth rate (3.94–4.05% day−1) and weight gain (66.80–71.85 g fish−1) were significantly higher in the Sangrovit®-fed groups. With the exception of total leukocyte levels, which were elevated in fish fed Sangrovit®-supplemented diets, haematological and immunological parameters remained unaffected. Hepatic alanine aminotransferase activity and hepatosomatic index also remained unaffected in all fish groups. Compared to the control group, the allochthonous lactic acid bacteria (LAB) populations were lower in fish fed diets containing Sangrovit® at 75 and 100 mg kg−1. The present study demonstrates that Sangrovit® had a positive effect on tilapia growth performance with no apparent effects on carcass composition, hepatic function and health status. [Copyright &y& Elsevier]

Bacterial communities from the intestinal tract of rainbow trout were investigated to assess transient and resident microbial communities using both culture-based and culture-independent techniques. Viable counts attached to the intestinal mucosa were in the range of log 4.77–5.38 and log 6.67–6.79 CFU g−1 in the intestinal contents. Pseudomonas spp. and Enterobacteriaceae constituted nearly 80% of the allochthonous population but <60% of the autochthonous populations. This coincided with an elevated mucosal level of a group of Gram-positive rods from ∼2% in the digesta to 25–35% on the mucosa. This group was identified by 16S rRNA as Arthrobacter aurescens and Janibacter spp. HTCC2649. Analysis of denaturing gradient gel electrophoresis banding patterns showed complex communities in all intestinal regions. Similarity coefficients showed that mucosal communities were ∼70% similar to digesta communities and yet due to the presence of bands found uniquely either in the digesta or on the mucosa, the communities are distinctly different. Scanning electron microscopy confirmed mucosal bacterial populations and highlighted a possible localized colonization between mucosal folds. The study highlights the complexity of resident microbial communities that have not been fully explored in previous rainbow trout studies; this is especially true with probiotic/prebiotic investigations. [ABSTRACT FROM AUTHOR]

The microbiome plays an important role in lipid metabolism but how the introduction of probiotic communities affects host lipid metabolism is poorly understood. Using a multidisciplinary approach we addressed this knowledge gap using the zebrafish model by coupling high-throughput sequencing with biochemical, molecular and morphological analysis to evaluate the changes in the intestine. Analysis of bacterial 16S libraries revealed that Lactobacillus rhamnosus was able to modulate the gut microbiome of zebrafish larvae, elevating the abundance of Firmicutes sequences and reducing the abundance of Actinobacteria. The gut microbiome changes modulated host lipid processing by inducing transcriptional down-regulation of genes involved in cholesterol and triglycerides metabolism (fit2, agpat4, dgat2, mgll, hnf4α, scap, and cck) concomitantly decreasing total body cholesterol and triglyceride content and increasing fatty acid levels. L. rhamnosus treatment also increased microvilli and enterocyte lengths and decreased lipid droplet size in the intestinal epithelium. These changes resulted in elevated zebrafish larval growth. This integrated system investigation demonstrates probiotic modulation of the gut microbiome, highlights a novel gene network involved in lipid metabolism, provides an insight into how the microbiome regulates molecules involved in lipid metabolism, and reveals a new potential role for L. rhamnosus in the treatment of lipid disorders. [ABSTRACT FROM AUTHOR]

The present study aimed to investigate whether alternative dietary protein sources modulate the microbial communities in the distal intestine (DI) of Atlantic salmon, and whether alterations in microbiota profiles are reflected in modifications in host intestinal function and health status. A 48-day feeding trial was conducted, in which groups of fish received one of five diets: a reference diet in which fishmeal (diet FM) was the only protein source and four experimental diets with commercially relevant compositions containing alternative ingredients as partial replacements of fishmeal, i.e., poultry meal (diet PM), a mix of soybean meal and wheat gluten (diet SBMWG), a mix of soy protein concentrate and poultry meal (diet SPCPM), and guar meal and wheat gluten (diet GMWG). Samples were taken of DI digesta and mucosa for microbial profiling using high-throughput sequencing and from DI whole tissue for immunohistochemistry and expression profiling of marker genes for gut health. Regardless of diet, there were significant differences between the microbial populations in the digesta and the mucosa in the salmon DI. Microbial richness was higher in the digesta than the mucosa. The digesta-associated bacterial communities were more affected by the diet than the mucosa-associated microbiota. Interestingly, both legume-based diets (SBMWG and GMWG) presented high relative abundance of lactic acid bacteria in addition to alteration in the expression of a salmon gene related to cell proliferation (pcna). It was, however, not possible to ascertain the cause-effect relationship between changes in bacterial communities and the host's intestinal responses to the diets. [ABSTRACT FROM AUTHOR]

A study was carried out to investigate the combined effect of exogenous enzymes and probiotic supplementation on tilapia growth, intestinal morphology and microbiome composition. Tilapia (34.56 ± 0.05 g) were fed one of four diets (35% protein, 5% lipid); one of which was a control and the remaining three diets were supplemented with either enzymes (containing phytase, protease and xylanase), probiotic (containing Bacillus subtilis , B acillus licheniformis and B acillus pumilus ) or enz-pro (the combination of the enzymes and probiotic). Tilapia fed diet supplemented with enz-pro performed better ( P < 0.05) than tilapia fed the control and probiotic supplemented diets in terms of final body weight (FBW), specific growth rate (SGR), feed conversion ratio (FCR) and protein efficiency ratio (PER). The dietary treatments did not affect somatic indices. The serum lysozyme activity was significantly higher ( P < 0.05) in tilapia fed the probiotic supplemented diet than of those fed the remaining experimental diets. The intestinal perimeter ratio was higher ( P < 0.05) in tilapia fed enz-pro supplemented diet when compared to those fed with the control and probiotic supplemented diets. Goblet cells abundance, microvilli diameter and total enterocyte absorptive surface was higher ( P < 0.05) in tilapia fed diet supplemented with enz-pro than those fed the control diet. High-throughput sequencing revealed that majority of reads derived from the tilapia digesta belonged to members of Fusobacteria (predominantly Cetobacterium ) distantly followed by Proteobacteria and Firmicutes. The alpha and beta diversities did not differ among dietary treatments indicating that the overall microbial community was not modified to a large extent by dietary treatment. In conclusion, supplementation of the diet with a combination of enzymes and probiotic is capable of improving tilapia growth and intestinal morphology without deleterious effect on the intestinal microbial composition. Statement of relevance 1. Intensive operations in aquaculture are often accompanied by sub-optimum environmental conditions which may be stressful for fish. 2. The production of high quality aquafeed with optimal growth and immune boosting effects could benefit intensive aquaculture operations. 3. Dietary supplementation of exogenous digestive enzymes and probiotic as a cocktail may result in complimentary mode of action. 4. Previous studies did not investigate the combined effects of exogenous digestive enzymes and probiotic on Nile tilapia. [ABSTRACT FROM AUTHOR]