Effects of dietary live and heat-inactive baker's yeast on growth, gut health, and disease resistance of Nile tilapia under high rearing density

Synergistic Effect of Dietary Supplementation with Sodium Butyrate, β-Glucan and Vitamins on Growth Performance, Cortisol Level, Intestinal Microbiome and Expression of Immune-Related Genes in Juvenile African Catfish (Clarias gariepinus)

The effect of dietary supplementation with sodium butyrate, β-glucan and vitamins (A, D3, E, K, C) on breeding indicators and immune parameters of juvenile African catfish was examined. The fish were fed with unenriched (group C) and enriched feed with a variable proportion of sodium butyrate/β-glucan, and constant content of vitamins (W1-W3). After the experiment, blood and the middle gut were collected. The microbiome of the gut was determined using Next Generation Sequencing (NGS). Liver tissue was collected for determination of expression of immune-related genes (HSP70, IL-1β, TNFα). W2 and W3 were characterized by the most favorable values of breeding indicators (p < 0.05). The highest blood cortisol concentration was in group C (71.25 ± 10.45 ng/mL), and significantly the lowest in W1 (46.03 ± 7.01 ng/ mL) (p < 0.05). The dominance of Cetobacterium was observed in all study groups, with the largest share in W3 (65.25%) and W1 (61.44%). Gene expression showed an increased number of HSP70 genes in W1. IL-1β and TNFα genes peaked at W3. The W3 variant turns out to be the most beneficial supplementation, due to the improvement of breeding and immunological parameters. The data obtained can be used to create a preparation for commercial use in the breeding of this species.

The effect of stabilized culture of Lactobacillus rhamnosus GCC-3 on gut and liver health, and anti-viral immunity of zebrafish

Probiotics are promising antibiotics alternatives to improve growth and disease resistance of cultured fish. Our study aimed to investigate the effect of dietary stabilized culture of Lactobacillus rhamnosus GCC-3 on growth performance, gut and liver health and anti-viral ability of zebrafish (Danio rerio). Zebrafish (0.161 ± 0.001 g) were fed control and the experimental diet containing 1% GCC-3 culture (1 × 107 CFU/g diet) for four weeks. Growth performance and gut and liver health parameters were monitored after four weeks feeding. The gut microbiota was analyzed by 16S rRNA gene sequencing. In another experiment, zebrafish (0.212 ± 0.001 g) were fed with basal or GCC-3 diets and challenged by spring viremia of carp virus (SVCV) at the end of feeding. The antiviral immune response was evaluated at 2nd and 4th days post SVCV infection and survival rate was calculated 14 days after challenge. The results showed that adding 1% GCC-3 significantly improved growth performance of zebrafish (P < 0.05). The intestinal expression of hypoxia-inducible factor Hif-1α, tight junction protein ZO-1α and ZO-1β was significantly up-regulated in 1% GCC-3 group compared with control (P < 0.05). Besides, 1% GCC-3 decreased the content of MDA and increased total antioxidant capacity in the intestine, and the relative expression of SOD, GST and Gpxa was improved. The abundance of Proteobacteria was reduced while Firmicutes was enriched in the intestinal microbiota of 1% GCC-3 group compared with control (P < 0.05). Zebrafish fed 1% GCC-3 showed higher survival rate after SVCV challenge. Accordingly, the expression of antiviral genes in the spleen was increased at 2nd and 4th days post infection. In conclusion, our results indicate that dietary 1% GCC-3 supplementation can improve gut and liver health as well as antiviral immunity of zebrafish.

Yarrowia lipolytica biomass-a potential additive to boost metabolic and physiological responses of Nile tilapia

We studied the effects of Yarrowia lipolytica biomass on digestive enzymes, blood biochemical profile, energy metabolism enzymes, and proximate meat composition of Nile tilapias. The experiment was entirely randomized with four replications. The animals (n = 20 per repetition) were fed with 0%, 3%, 5%, and 7% of biomass for 40 days and then blood and liver were analyzed. There was an increase in the activities of chymotrypsin (5, 7% groups), trypsin (3, 5% groups), and sucrase (7% group) compared to the respective control groups. On the other hand, maltase activity was significantly reduced for all yeast biomass treatments, while the supplementation did not influence lipase and amylase activities. Moreover, the blood triacylglycerol concentrations were increased in the 7% group, while any treatment modified blood total cholesterol, glycemia, and hepatic glycogen content. Y. lipolytica biomass promoted significant increases in meat protein and lipid contents without changes in moisture and ash parameters. Furthermore, Y. lipolytica biomass promoted increases in hexokinase (3% group), phosphofructokinase (5, 7% groups), glucose-6-phosphate dehydrogenase (5% group), citrate synthase (3% group), aspartate aminotransferase and alanine aminotransferase (3% group), and glutamate dehydrogenase (3, 5% groups) compared to the respective control groups. At the same time, no changes were observed in the activity of glucose-6-phosphatase. Y. lipolytica biomass supplementation in tilapias' diet can modulate the digestive system and improve nutrient disponibility to the cells. Moreover, the changes in the metabolic profile and in energy metabolism can be correlated with the improvement of meat composition. Therefore, the Y. lipolytica biomass has a great potential to be used as a feed ingredient for Nile tilapias.

In-Situ Biofloc Affects the Core Prokaryotes Community Composition in Gut and Enhances Growth of Nile Tilapia (Oreochromis niloticus)

Biofloc technology is commonly applied in intensive tilapia (Oreochromis niloticus) culture to maintain water quality, supply the fish with extra protein, and improve fish growth. However, the effect of dietary supplementation of processed biofloc on the gut prokaryotic (bacteria and archaea) community composition of tilapia is not well understood. In this study one recirculating aquaculture system was used to test how biofloc, including in-situ biofloc, dietary supplementation of ex-situ live or dead biofloc, influence fish gut prokaryotic community composition and growth performance in comparison to a biofloc-free control treatment. A core gut prokaryotic community was identified among all treatments by analyzing the temporal variations in gut prokaryotes. In-situ produced biofloc significantly increased the prokaryotic diversity in the gut by reducing the relative abundance of dominant Cetobacterium and increasing the relative abundance of potentially beneficial bacteria. The in-situ biofloc delivered a unique prokaryotic community in fish gut, while dietary supplementation of tilapias with 5% and 10% processed biofloc (live or dead) only changed the relative abundance of minor prokaryotic taxa outside the gut core microbiota. The modulatory effect of in-situ biofloc on tilapia gut microbiota was associated with the distinct microbial community in the biofloc water and undisturbed biofloc. The growth-promoting effect on tilapia was only detected in the in-situ biofloc treatment, while dietary supplementation of processed biofloc had no effect on fish growth performance as compared to the control treatment.

Stabilized fermentation product of Cetobacterium somerae improves gut and liver health and antiviral immunity of zebrafish

Probiotics are widely used in aquafeeds and exhibited beneficial effects on fish by improving host health and resisting pathogens. However, probiotics applied to aquaculture are mainly from terrestrial sources instead of the host animal. The purpose of the work was to evaluate the effects of stabilized fermentation product of commensal Cetobacterium somerae XMX-1 on gut, liver health and antiviral immunity of zebrafish. A total of 240 zebrafish were assigned to the control (fed a basal diet) and XMX-1 group (fed a basal diet with 10 g XMX-1/kg diet). After four weeks feeding, growth performance, feed utilization, hepatic steatosis score, TAG, lipid metabolism related genes and serum ALT were evaluated. Furthermore, serum LPS, the expression of Hif-1α, intestinal inflammation score, antioxidant capability and gut microbiota were tested. The survival rate and the expression of antiviral genes were analyzed after challenge by spring viremia of carp virus (SVCV). Results showed that dietary XMX-1 did not affect growth of zebrafish. However, dietary XMX-1 significantly decreased the level of serum LPS, intestinal inflammation score and intestinal MDA, as well as increased T-AOC and the expression of Hif-1α in zebrafish intestine (p < 0.05). Furthermore, XMX-1 supplementation decreased the relative abundance of Proteobacteria and increased Firmicutes and Actinobacteria. Additionally, XMX-1 supplementation significantly decreased hepatic steatosis score, hepatic TAG, serum ALT and increased the expression of lipolysis genes versus control (p < 0.05). Zebrafish fed XMX-1 diet exhibited higher survival rate after SVCV challenge. Consistently, dietary XMX-1 fermentation product increased the expression of IFNφ2 and IFNφ3 after 2 days of SVCV challenge and the expression of IFNφ1, IFNφ2 and MxC after 4 days of SVCV challenge in the spleen in zebrafish versus control (p < 0.05). In conclusion, our results indicate that dietary XMX-1 can improve liver and gut health, while enhancing antiviral immunity of zebrafish.

Carotenoid coloration and coloration-linked gene expression in red tilapia (Oreochromis sp.) tissues

Background

Production, marketability and consumer preference of red tilapia often depends upon the intensity of coloration. Hence, new approaches to develop coloration are now geared to improve market acceptability and profit. This study evaluated the effects of carotenoid-rich diets on the phenotypic coloration, carotenoid level, weight gain and expression of coloration-linked genes in skin, fin and muscle tissues. Carotenoids were extracted from dried Daucus carota peel, Ipomoea aquatica leaves, and Moringa oleifera leaves. Eighty (80) size-14 fish were fed with carotenoid-rich treatments twice a day for 120 days. The phenotypic effect of the carotenoid extracts was measured through a color chart. Skin carotenoid level was measured through UV-vis spectrophotometer. csf1ra, Bcdo2 and StAR expression analysis was done using qRT-PCR.

Results

Treatments with carotenoid extracts yielded higher overall scores on phenotypic coloration and tissue carotenoid levels. Differential expression of carotenoid-linked genes such as the elevated expression in csf1ra and lower expression in Bcdo2b following supplementation of the enhanced diet supports the phenotypic redness and increased carotenoid values in red tilapia fed with D. carota peel and I. aquatica leaves.

Conclusions

Overall improvement in the redness of the tilapia was achieved through the supplementation of carotenoid-rich diet derived from readily available plants. Differential expression of coloration-linked genes supports the increase in the intensity of phenotypic coloration and level of carotenoids in the tissues. The study emphasizes the importance of carotenoids in the commercial tilapia industry and highlights the potential of the plant extracts for integration and development of feeds for color enhancement in red tilapia.

Short- and long-term probiotic effects of Enterococcus hirae isolated from fermented vegetable wastes on the growth, immune responses, and disease resistance of hybrid catfish (Clarias gariepinus × Clarias macrocephalus)

This study evaluated the short- and long-term effects of dietary supplementation with Enterococcus hirae strain UPM02 on the growth performance, immunity, and disease resistance of hybrid catfish (Clarias gariepinus × Clarias macrocephalus) against Aeromonas hydrophila infection. In the long-term trial, fingerling fish were fed diets containing 0 (control), 2 × 10⁵, or 2 × 10⁷ CFU/g E. hirae UPM02 for 120 days. Administration of E. hirae UPM02 had significant effects on the specific growth rate (SGR), feed utilization efficiency, body indices (P < 0.05), and gut villus physiology of the catfish. E. hirae UPM02 application also significantly increased the complete blood cell counts, phagocytic activity, respiratory burst, lysozyme activity, and alternative complement pathway hemolytic (ACH₅₀) activity in tested catfish throughout the experimental periods (P < 0.05). Dietary E. hirae UPM02 at both concentrations significantly increased the expression levels of the alpha-2-macroglobulin (α2M), CC chemokines, CXC chemokines, lysozyme c (LYZC), myeloperoxidase (MYE), NF-kappa-B1 p105 subunit (NF-K), and bactericidal permeability-increasing protein (BPIP) genes in the head kidney, liver, and spleen (P < 0.05) at days 80, 100 and 120 after application. However, heat shock protein 70 (HSP70) gene expression was slightly downregulated in these organs. Interestingly, fish fed the diets containing 2 × 10⁵ and 2 × 10⁷ CFU/g E. hirae UPM02 exhibited a significantly lower (P < 0.05) postchallenge mortality rates (32% and 30%, respectively) after 14 days of A. hydrophila challenge than the control fish (58%). In short-term (28 days) application to juvenile catfish, the two concentrations of E. hirae did not affect all growth parameters. Nevertheless, these concentrations markedly elevated all tested immune parameters, similarly to long-term application. Immune-related gene expression was significantly upregulated at day 28 in the head kidney, at day 14 in the liver, and at day 7 in the spleen in fish treated with the two concentrations of the probiotics (P < 0.05). Mortality at 14 days after challenge with A. hydrophila in the groups receiving the two concentrations of the probiotic was significantly lower than that in the control group, at 28, 24, and 48%, respectively (P < 0.05). These results collectively suggest that dietary supplementation with E. hirae UPM02 at 2 × 10⁵ and 2 × 10⁷ CFU/g effectively influenced immune responses, enhanced disease protection, and stimulated immunity-related gene expression in hybrid catfish under both short- and long-term application. However, growth enhancement was significantly evidenced with long-term application only.

The Effect of Stocking Density and Carbon Sources on the Oxidative Status, and Nonspecific Immunity of Nile tilapia (Oreochromis niloticus) Reared under Biofloc Conditions

Simple Summary

The present study investigated the effect of stocking density and dietary carbon sources on the water quality, oxidative status and immune-related of Nile tilapia (Oreochromis niloticus) reared under biofloc conditions (BFT). Eight groups were established at two levels of stocking densities (140 fish per m³: low stocking density, LSD) and (280 fish per m³: high stocking density, HSD) (5.15 ± 1.12 g) and kept in eight biofloc units containing water without carbon sources (control groups) or with glycerol, molasses, or starch. Overall, this study has reported that immune response gene expression is better in LSD than HSD and improved by carbon addition. More specifically, based on the overall performances of tilapia reared under LSD or HSD, using molasses is recommended as a carbon source to promote the performances and health status of Nile tilapia cultured in a biofloc system.

Abstract

The present study investigated the effect of stocking density and dietary carbon sources on the water quality, oxidative status, and immune-related genes of Nile tilapia (Oreochromis niloticus) reared under biofloc conditions (BFT). Eight groups were established at two levels of stocking densities (140 fish per m³: low stocking density, LSD) and (280 fish per m³: high stocking density, HSD) (5.15 ± 1.12 g) and kept in eight biofloc units containing water without carbon sources (control groups) or with glycerol, molasses, or starch. Red blood cells count, hemoglobin, and hematocrit values were reduced in fish stocked in control groups at LSD and HSD than biofloc groups. Control fish groups reared at both LSD and HSD have the highest significant (p < 0.05) white blood cells number than other fish groups. Meanwhile, fish groups that received glycerol, molasses, and starch maintained in both LSD and HSD presented a higher significant (p < 0.05) monocyte % than in the control group reared at both LSD and HSD. The fish group reared in biofloc conditions (BFT) using starch carbon source and reared at the HSD presented a significantly higher (p < 0.05) increase in total serum protein and albumin levels as well as globulin value than the control fish group reared at both LSD and HSD. The highest glucose and cortisol levels were showed in the control fish group reared at both LSD and HSD. Fish maintained in glycerol-based biofloc at LSD attained the highest (p < 0.05) serum superoxide dismutase (SOD), glutathione reductase (GR), and catalase than other experimental groups. Regarding the nonspecific immune status, significantly increased expression of CC-chemokines, CXC-chemokines, TLR7 and IL-8 genes was found in molasses based biofloc groups. The data of the present study revealed that using molasses promotes health status of Nile tilapia cultured in a biofloc system.

Citrobacter Species Increase Energy Harvest by Modulating Intestinal Microbiota in Fish: Nondominant Species Play Important Functions

This study shows that the ability of gut microbiota members to enhance host energy harvest from a high-fat diet is a conserved feature of host-microbe interactions in fish, as in mammals. It also underscores that gut microbiota members are able to significantly impact host biology even when at low abundance.

An efficient energy harvesting mechanism is likely critical for animals in their natural environment. Intestinal microbiota enriched by a high-fat diet aid in lipid accumulation, a strategy likely evolved for energy harvest in mammals. However, whether this strategy is conserved among vertebrate organisms remains unclear. A bacterial strain (S1), enriched on soybean oil rich medium, was isolated from the gut of Nile tilapia and demonstrated to be a member of the Citrobacter genus. Although a high-fat diet increased the number of Citrobacter spp., these bacteria were not abundant in the intestine by high-throughput sequencing. Addition of bacterium S1 to a high-fat diet modulated intestinal microbial composition and increased high-fat diet-induced lipid accumulation in mesenteric adipose tissue, accompanied by (i) increased triglyceride absorption efficiency and triglyceride reesterification and (ii) increased intestinal permeability. Collectively, our results provide evidence that specific intestinal bacteria aid the host in harvesting more energy from a high-fat diet in fish. Furthermore, the results from the present study also suggest that nondominant bacteria in the gut may play an important role in regulating host metabolism.

IMPORTANCE This study shows that the ability of gut microbiota members to enhance host energy harvest from a high-fat diet is a conserved feature of host-microbe interactions in fish, as in mammals. It also underscores that gut microbiota members are able to significantly impact host biology even when at low abundance.

Effects of dietary Lactobacillus rhamnosus JCM1136 and Lactococcus lactis subsp. lactis JCM5805 on the growth, intestinal microbiota, morphology, immune response and disease resistance of juvenile Nile tilapia, Oreochromis niloticus

The present study aimed to evaluate the individual and combined effects of Lactobacillus rhamnosus (LR) JCM1136 and Lactococcus lactis subsp. lactis (LL) JCM5805 on the growth, intestinal microbiota, intestinal morphology, immune response and disease resistance of juvenile Nile tilapia (Oreochromis niloticus). A total of 720 apparently healthy juvenile Nile tilapia (0.20 ± 0.05 g) were randomly divided into four equal groups. Fish were fed with a basal diet (CK) supplemented with JCM1136 (LR), JCM5805 (LL), and JCM1136 + JCM5805 (LR+LL) at 1 × 10⁸ CFU/g basal diet for 6 weeks, followed by a basal diet for 1 week. After 6 weeks of feeding, the LL treatment significantly increased the growth and feed utilization of Nile tilapia when compared with the CK. Light microscopy and transmission electron microscopy images of the midgut revealed that probiotic supplementation significantly increased gut microvilli length and microvilli density compared to CK. The transcript levels of several key immune-related genes in the mid-intestine and liver of fish were analyzed by means of quantitative polymerase chain reaction (qPCR) at the end of the sixth week. The results showed the following: when compared to CK group, fish in LR had significantly increased transcript levels of IFN-γ, lyzc, hsp70 and IL-1β in the intestine; LL fish showed significantly increased expressions of TNF-α, IFN-γ, lyzc, hsp70 and IL-1β in the intestine and liver; and intestine lyzc, hsp70 and IL-1β and liver TNF-α, IFN-γ, hsp70 and IL-1β were significantly increased in LR+LL fish. Following a 6-week period of being fed probiotics or a control diet, the tilapia were challenged with an intraperitoneal injection of 20 μl of the pathogenic Streptococcus agalactiae (WC1535) (1 × 10⁵ CFU/ml). The survival rates of the probiotic-fed groups were significantly higher than that of the CK group, and the LL group had the highest survival rate. High-throughput sequencing revealed a significantly higher presence of JCM5805 in the guts of LL fish during the period of probiotic application, but this was no longer detected in all LL samples 1 week post cessation of probiotic administration. Cessation of probiotic administration led to disorders of individual gut microbes within the LR and LL groups. Statistical analysis (LEfSe) demonstrated that three phyla, namely, Bacteroidetes, Fusobacteria and Actinobacteria were enriched in the CK group, while the abundance of Proteobacteria was greater in the probiotic-fed fish. At the genus level, Plesiomonas, which includes potential pathogens of fish, were significantly decreased in the probiotic-fed groups. In contrast, a significant increase of Rhizobium and Achromobacter, which can produce a variety of enzymes with cellulolytic and pectolytic activity, were observed in fish fed with probiotics, indicating that dietary probiotics were helpful in the propagation of some probiotic bacteria. Our data revealed that JCM1136 and JCM5805, as a feed additive at 10⁸ CFU/g feed, could improve intestinal morphology, enhance immune status and disease resistance, and affect the gut microbiota of tilapia; thus, these additives could be used as probiotics for juvenile Nile tilapia. JCM5805 was more effective than JCM1136 or the mixture of the two for promoting the growth, enhancing the immune status and disease resistance of tilapia.

Dietary yeast Sterigmatomyces halophilus enhances mucosal immunity of gilthead seabream (Sparus aurata L.)

A yeast was isolated from hypersaline sediments, grown and phylogenetically characterized as Sterigmatomyces halophilus strainN16. The dietary administration of this yeast was studied for its effect on skin mucosal immune and antioxidant status of gilthead seabream (Sparus aurata L.). Fish were fed a commercial diet (control, non-supplemented diet), or the same commercial diet supplemented with 0.55% or 1.1% of yeast for 15 and 30 days. One month after the end of the trial, fish from all treatments were intraperitoneally injected with pathogenic Vibrio parahaemolyticus and further fed with the same diets for one week, after which fish were also sampled. Significant increases were observed in the immune activities determined in the fish fed the yeast supplemented diets compared with the values recorded in mucus of fish from the control group. The expression levels of trypsin (one of the main digestive enzymes) and several immune-related genes (IL-1β, TNF-α, IgM, C3 and lysozyme) were also evaluated by real-time PCR in intestine and skin. Interestingly, trypsin gene expression in intestine was up regulated in both experimental diets compared with the control group, particularly in fish fed with 0.55% of S. halophilus at any time of the experimental trial. Immune-related genes in intestine and skin were strongly expressed principally in fish fed with 0.55% of S. halophilus for 15 days and 1.1% for 30 days and after infection, respectively. The present results suggest that the yeast S. halophilus can be considered as a novel fish immunostimulant. The excellent potential of marine microorganisms isolated from extreme environments with beneficial properties for fish is discussed.

Performance of Clarias gariepinus Fed Dried Brewer's Yeast (Saccharomyces cerevisiae) Slurry in Replacement for Soybean Meal

Following disparity of earlier results, this study tested the performance of African catfish Clarias gariepinus fed dried brewer's yeast slurry meal (DBYM) based diets. Fingerlings of C. gariepinus with pooled mean initial weight of 1.58 ± 0.01 g were stocked in hapas (1 m × 1 m × 1 m) immersed in an earthen pond at a density of 15 fish per cage. Five diets with increasing substitution of soybean meal with 25%, 50%, 75%, and 100% of dried brewer's yeast and a control without dried brewer's yeast (0% substitution) were evaluated for 8 weeks. Palatability of diets reduced with increasing levels of DBYM. Growth and utilization parameters such as weight gain, feed conversion ratio, protein efficiency ratio, and specific growth rate differed significantly (p < 0.05) among treated groups. Specific growth rate decreased with increasing substitution while the best feed conversion ratio was obtained in the diet devoid of DBYM. Protein efficiency and utilization decreased with increasing levels of DBYM. Body composition was also affected by inclusion of DBYM with significant differences (p < 0.05) being observed across the diets. The trend in body composition follows the utilization of the diets. We conclude that the optimal range of inclusion and substitution of soybean meal with DBYM in C. gariepinus feed is between 1% and 14% of dry matter.

Protective Yeasts Control V. anguillarum Pathogenicity and Modulate the Innate Immune Response of Challenged Zebrafish (Danio rerio) Larvae

We investigated mechanisms involved in the protection of zebrafish (Danio rerio) larvae by two probiotic candidate yeasts, Debaryomyces hansenii 97 (Dh97) and Yarrowia lypolitica 242 (Yl242), against a Vibrio anguillarum challenge. We determined the effect of different yeast concentrations (104-107 CFU/mL) to: (i) protect larvae from the challenge, (ii) reduce the in vivo pathogen concentration and (iii) modulate the innate immune response of the host. To evaluate the role of zebrafish microbiota in protection, the experiments were performed in conventionally raised and germ-free larvae. In vitro co-aggregation assays were performed to determine a direct yeast-pathogen interaction. Results showed that both yeasts significantly increased the survival rate of conventionally raised larvae challenged with V. anguillarum. The concentration of yeasts in larvae tended to increase with yeast inoculum, which was more pronounced for Dh97. Better protection was observed with Dh97 at a concentration of 106 CFU/mL compared to 104 CFU/mL. In germ-free conditions V. anguillarum reached higher concentrations in larvae and provoked significantly more mortality than in conventional conditions, revealing the protective role of the host microbiota. Interestingly, yeasts were equally (Dh97) or more effective (Yl242) in protecting germ-free than conventionally-raised larvae, showing that protection can be exerted only by yeasts and is not necessarily related to modulation of the host microbiota. Although none of the yeasts co-aggregated with V. anguillarum, they were able to reduce its proliferation in conventionally raised larvae, reduce initial pathogen concentration in germ-free larvae and prevent the upregulation of key components of the inflammatory/anti-inflammatory response (il1b, tnfa, c3, mpx, and il10, respectively). These results show that protection by yeasts of zebrafish larvae challenged with V. anguillarum relates to an in vivo anti-pathogen effect, the modulation of the innate immune system, and suggests that yeasts avoid the host-pathogen interaction through mechanisms independent of co-aggregation. This study shows, for the first time, the protective role of zebrafish microbiota against V. anguillarum infection, and reveals mechanisms involved in protection by two non-Saccharomyces yeasts against this pathogen.