Probiotic Pediococcus acidilactici modulates both localised intestinal- and peripheral-immunity in tilapia (Oreochromis niloticus)

Correlation Analysis of the Transcriptome and Gut Microbiota in Salmo trutta Resistance to Aeromonas salmonicida

Aeromonas salmonicida is a major pathogenic bacterium that poses a significant threat to salmonid fish. Yadong County, located in the Xizang Autonomous Region, is renowned for its characteristic industry of Salmo trutta aquaculture. In recent years, the outbreak of Bacterial Gill Disease (BGD) has led to substantial economic losses for S. trutta farmers. Our prior research identified A. salmonicida as one of the primary culprits behind BGD. To mitigate the impact of A. salmonicida on S. trutta, we conducted a comprehensive study aimed at identifying genes associated with resistance to A. salmonicida. This involved transcriptome sequencing and 16S rRNA sequencing of intestinal flora, providing valuable insights for the study of disease resistance in S. trutta. In this study, we identified 324 genera with 5171 ASVs in the susceptible group and 293 genera with 5669 ASVs in the resistant group. Notably, Methylobacterium and Sphingomonas were common bacteria present in the salmon's gut, and their proportions remained relatively stable before and after infection. Shewanella, with its antagonistic relationship with Aeromonas, may play a crucial role in the salmon's defense against A. salmonicida. Several related genes were identified, including angptl4, cipcb, grasp, ccr9a, sulf1, mtmr11, B3GNT3, mt2, PLXDC1, and ank1b.

Growth performance, mucosal immunity and disease resistance in goldfish (Carassius auratus) orally administered with Escherichia coli Strain Nissle 1917

The current research aimed to shed light on the efficacy of Escherichia coli strain Nissle 1917 (EcN) on goldfish (……) growth, gut immunity, morphology, bacterial nutritional enzyme activity and resistance to Aeromonas hydrophila infection. Fish fed with EcN at 106, 107 and 108 CFU/g feed for 80 days showed an enhancement in growth better than control fish. The gut innate immunity in terms of lysozyme activity, immunoglobulin and total protein levels was increased in the treatment fish with the best result being observed in fish fed EcN at 108 CFU/ g. In addition, an increase was noted in the upregulation of immune-relevant genes, namely lysozyme, interleukin-1β, inducible nitric oxide synthase and tumor necrosis factor α of fish intestine. A marked surge in the number of proteolytic and heterotrophic bacteria was noted in the gut of fish nourished with the probiotic. Histological studies exhibited an improvement in the intestinal absorption surface area, intraepithelial lymphocyte count and goblet cell density. Significantly higher survival rate was obtained in fish fed EcN at 108 CFU/g compared with the fish fed with the basal diet. These data exhibited the beneficial effect of EcN on goldfish growth, digestive enzymes, intestine heterotrophic bacteria and resistance against Aeromonas hydrophila challenge. This study confirmed the favorable outcomes resulting from the administration of EcN at108 CFU/g.

Integrative analysis of metagenome and metabolome provides new insights into intestinal health protection in Coilia nasus larvae via probiotic intervention

With the development of large-scale intensive feeding, growth performance and animal welfare have attracted more and more attention. Exogenous probiotics can promote the growth performance of fish through improving intestinal microbiota; however, it remains unclear whether intestinal microbiota influence physiological biomarkers. Therefore, we performed metagenomic and metabolomic analysis to investigate the effects of a 90-day Lactiplantibacillus plantarum supplementation to a basal diet (1.0 × 108 CFU/g) on the growth performance, intestinal microbiota and their metabolites, and physiological biomarkers in Coilia nasus larvae. The results showed that the probiotic supplementation could significantly increase weight and body length. Moreover, it could also enhance digestive enzymes and tight junctions, and inhibit oxidative stress and inflammation. The metagenomic analysis showed that L. plantarum supplementation could significantly decrease the relative abundance of Proteobacteria and increase the relative abundance of Firmicutes. Additionally, pathogenic bacteria (Aeromonadaceae, Aeromonas, and Enterobacterales) were inhibited and beneficial bacteria (Bacillales) were promoted. The metabolome analysis showed that acetic acid and propanoic acid were significantly elevated, and were associated with Kitasatospora, Seonamhaeicola, and Thauera. A correlation analysis demonstrated that the digestive enzymes, tight junction, oxidative stress, and inflammation effects were significantly associated with the increased acetic acid and propanoic acid levels. These results indicated that L. plantarum supplementation could improve intestinal microbial community structure and function, which could raise acetic acid and propanoic acid levels to protect intestinal health and improve growth performance in C. nasus larvae.

Genes expression in Penaeus monodon of Bangladesh; challenged with AHPND-causing Vibrio parahaemolyticus

Vibrio parahaemolyticus, the causative agent of Acute hepatopancreatic necrosis disease (AHPND), was discovered in 2013 as a unique isolate that produces toxins and kills penaeid shrimps in devasting nature in Bangladesh and causes severe economic losses. This research aimed to understand the expressions of immune genes in different stages of the host species, Penaeus monodon, against virulence and toxin genes upon being challenged with V. parahaemolyticus. Healthy post-larvae (PL) samples were collected from southwestern of Bangladesh from July 2021 to August 2022. The tryptic soy agar with 1.5% sodium chloride (NaCl) was used to inoculate the cells of V. parahaemolyticus, and the tryptic soy broth (TSB) with 1.5% NaCl was used to transfer the colonies. The spectrophotometry measured bacteria density. PCR, qPCR, SDS-PAGE, and Western blot measured gene expression and survivability after the immersion challenge. The 1 × 105CFU/mL of V. parahaemolyticus was used for 144 h.p.i (hours post-infection) challenge to six stages of post-larvae (PL) of P. monodon (PL20, PL25, PL30, PL35, PL40, and PL45), PL30 and PL35 showed 100% mortality by day 72 (h.p.i.) after exposure that indicated most vulnerable to V. parahaemolyticus. The expression of immune and toxic genes was confirmed by qPCR. The immune genes toll-like receptors (TLR), prophenoloxidase (ProPO), lysozyme (lyso), and penaeidin (PEN) of PL20 and PL25 of P. monodon were expressed robustly up-trends. PL30 and PL35 showed the lowest gene expression at the end of 72 (h.p.i.). At the end of the 144 (h.p.i.) exposure, the immune genes TLR, ProPO, lyso, and PEN expressed highest in PL45 than other post-larvae stages of P. monodon. The toxic genes (pirA, ToxR, ToxA, ToxB, tlh, tdh, and trh) in PL30 and PL35 of P. monodon after exposure of V. parahaemolyticus were expressed highest at the end of the 72 (h.p.i.). The lowest toxic genes expressions were revealed in PL20 and PL45 at the end of the 144 (h.p.i.). The SDS-PAGE analysis of proteins from the bacterium revealed identical protein profiles with toxic genes, and those toxins were further confirmed by Western blot. The 20 kDa, 78 kDa (ToxR), 20 kDa, 25 kDa (ToxA), 25 kDa (ToxB), 20 kDa, 27 kDa, 75 kDa (tdh), and 20 kDa, 27 kDa, 75 kDa, and 78 kDa (trh) proteins were strong responses in Western blot, indicating the crucial involvement of these immune-related genes in the defense and recovery of the first-line defense mechanisms during V. parahaemolyticus infection to shrimp. The all-toxic genes showed a unique homology and those derived from the common ancestor compared with V. parahaemolyticus (NCBI accession no. AP014859.1). All clades were derived with different traits with very low genetic distance, where the overall mean distance was 3.18 and showed a very uniform and homogenous pattern among the lineages. The V. parahaemolyticus infection process in different PL stages in P. monodon revealed novel insights into the immune responses. The responses may lead to the subsequent production of a DNA vaccine, enhancing shrimp health management to minimize the economic losses due to AHPND experiencing an outbreak of early mortality syndrome (EMS) toward sustainable production P. monodon (shrimp).

Combined Dietary Administration of Chlorella fusca and Ethanol-Inactivated Vibrio proteolyticus Modulates Intestinal Microbiota and Gene Expression in Chelon labrosus

The use of functional feeds in aquaculture is currently increasing. This study aimed to assess the combined impact of dietary green microalgae Chlorella fusca and ethanol-inactivated Vibrio proteolyticus DCF12.2 (CVP diet) on thick-lipped grey mullet (Chelon labrosus) juvenile fish. The effects on intestinal microbiota and the transcription of genes related to metabolism, stress, and the immune system were investigated after 90 days of feeding. Additionally, the fish were challenged with Aeromonas hydrophila and polyinosinic-polycytidylic acid (poly I:C) to evaluate the immune response. Microbiota analysis revealed no significant differences in alpha and beta diversity between the anterior and posterior intestinal sections of fish fed the control (CT) and CVP diets. The dominant genera varied between the groups; Pseudomonas and Brevinema were most abundant in the CVP group, whereas Brevinema, Cetobacterium, and Pseudomonas were predominant in the CT group. However, microbial functionality remained unaltered. Gene expression analysis indicated notable changes in hif3α, mhcII, abcb1, mx, and tnfα genes in different fish organs on the CVP diet. In the head kidney, gene expression variations were observed following challenges with A. hydrophila or poly I:C, with higher peak values seen in fish injected with poly I:C. Moreover, c3 mRNA levels were significantly up-regulated in the CVP group 72 h post-A. hydrophila challenge. To conclude, incorporating C. fusca with V. proteolyticus in C. labrosus diet affected the microbial species composition in the intestine while preserving its functionality. In terms of gene expression, the combined diet effectively regulated the transcription of stress and immune-related genes, suggesting potential enhancement of fish resistance against stress and infections.

Histomorphological Changes in Fish Gut in Response to Prebiotics and Probiotics Treatment to Improve Their Health Status: A Review

The gastrointestinal tract (GIT) promotes the digestion and absorption of feeds, in addition to the excretion of waste products of digestion. In fish, the GIT is divided into four regions, the headgut, foregut, midgut, and hindgut, to which glands and lymphoid tissues are associated to release digestive enzymes and molecules involved in the immune response and control of host-pathogens. The GIT is inhabited by different species of resident microorganisms, the microbiota, which have co-evolved with the host in a symbiotic relationship and are responsible for metabolic benefits and counteracting pathogen infection. There is a strict connection between a fish's gut microbiota and its health status. This review focuses on the modulation of fish microbiota by feed additives based on prebiotics and probiotics as a feasible strategy to improve fish health status and gut efficiency, mitigate emerging diseases, and maximize rearing and growth performance. Furthermore, the use of histological assays as a valid tool for fish welfare assessment is also discussed, and insights on nutrient absorptive capacity and responsiveness to pathogens in fish by gut morphological endpoints are provided. Overall, the literature reviewed emphasizes the complex interactions between microorganisms and host fish, shedding light on the beneficial use of prebiotics and probiotics in the aquaculture sector, with the potential to provide directions for future research.

Understanding Age-Related Longitudinal Dynamics in Abundance and Diversity of Dominant Culturable Gut Lactic Acid Bacteria in Pastured Goats

Understanding gut lactic acid bacteria (LAB) in healthy hosts is an important first step in selecting potential probiotic species. To understand the dynamics of LAB in healthy goats, a cohort of thirty-seven healthy new-born goat kids was studied over a ten-month period. Total LAB was quantified using SYBR green qPCR. Seven hundred LAB isolates were characterized using microscopy, M13 RAPD genotyping and 16S rDNA sequencing. The highest and lowest LAB counts were detected at one week and ten months of age, respectively. Diverse LAB species were detected, whose identity and prevalence varied with age. The main isolates belonged to Limosilactobacillus reuteri, Limosilactibacillus fermentum, Lactobacillus johnsonni, Ligilactobacillus murinus, Ligilactobacillus salivarius, Limosilactobacillus mucosae, Lactiplantibacillus plantarum, Ligilactobacillus agilis, Lactobacillus acidophilus/amyolovolus, Pediococcus spp. and Enterococcus spp. Uniquely, L. reuteri and Pediococcus spp. were most common in pre- and peri-weaned goats, while Lactobacillus mucosae and Enterococcus spp. were predominant in goats one month and older. Based on RAPD genotyping, L. reuteri had the highest genotypic diversity, with age being a factor on the genotypes detected. This data may be relevant in the selection of age-specific probiotics for goats. The findings may also have broader implications by highlighting age as a factor for consideration in probiotic bacteria selection in other animal hosts.

Effects of salinity on growth, physiology, biochemistry and gut microbiota of juvenile grass carp (Ctenopharyngodon idella)

Grass carp (Ctenopharyngodon idella) is among the most important freshwater fish species in China. However, it remained unclear how salinity could affect grass carp. Two experiments were performed. The first experiment was a 4-day acute salt tolerance experiment with six salinities (0, 4, 8, 12, 16, and 20 ppt). The second experiment was an 8-week chronic salt stress experiment with three salinities (0, 2 and 6 ppt). To investigate the intestinal bacterial community of grass carp from three salinities (0, 2, and 6 ppt), the 16S rDNA sequencing was performed. The results showed that grass carp exhibited great adaptability to low salinity (2 ppt), with no significant difference in growth and maintained stable physiological and immune status. However, exposed to high salinity (6 ppt) caused significant deleterious effects on grass carp, including growth inhibition as well as physiological and immune-related changes. The gut microbiota in grass carp changed with salinity. With the increase of salinity, the proportion of beneficial bacteria in the gut of grass carp gradually decreased, while some harmful bacteria gradually occupied the dominant position. Changes in gut microbial composition ultimately affected the growth of grass carp. This study helps further clarify the effects of salinity on grass carp.

Effects of Bacillus spp. Mixture on Growth, Immune Responses, Expression of Immune-Related Genes, and Resistance of Nile Tilapia Against Streptococcus agalactiae Infection

The purpose of this study was to evaluate the effect of Bacillus spp. mixture (Bacillus subtilis TISTR001, Bacillus megaterium TISTR067, and Bacillus licheniformis DF001) (1 × 10⁶ CFU/g) on growth, immune parameters, immune-related gene expression, and resistance of Nile tilapia against Streptococcus agalactiae AAHM04. Fish were fed different concentrations of Bacillus spp. 0 (control; T1), 1 (T2), 3 (T3), and 5 (T4) g/kg diets for 120 days. The results showed that weight gain, average daily gain, specific growth rate, feed conversion ratio in T3 diet were significantly higher than the control group and other tested diets (p < 0.05). Immune parameters, such as myeloperoxidase and lysozyme, were significantly higher in the T3 and T4 diets compared to the control group (p < 0.05). Similarly, IL-1β and TNF-α gene expressions in the spleen of fish fed T2, T3, and T4 diets were significantly higher than the control group (p < 0.05). However, no significant differences in survival rate, hematology, blood chemical indices, malondialdehyde (MDA) levels, body chemical composition, and organosomatic indices (p > 0.05) were noticed in all treatments. No significant differences in survival rate after the challenge test with S. agalactiae AAHM04 were found in fish fed Bacillus spp. mixture diets, except for the T3 diet. These results suggest that Bacillus spp. mixture diet at 3 g/kg diet (T3) could improve growth, immune response, and disease resistance of Nile tilapia.

In Vitro Evaluation of Postbiotics Produced from Bacterial Isolates Obtained from Rainbow Trout and Nile Tilapia against the Pathogens Yersinia ruckeri and Aeromonas salmonicida subsp. salmonicida

The use of antibiotics in aquaculture leads to the proliferation of multidrug-resistant bacteria, and an urgent need for developing new alternatives to prevent and control disease has, thus, arisen. In this scenario, postbiotics represent a promising tool to achieve this purpose; thus, in this study, isolation and selection of bacteria to further produce and evaluate their postbiotics antibacterial activity against fish pathogens was executed. In this respect, bacterial isolates from rainbow trout and Nile tilapia were obtained and tested in vitro against Yersinia ruckeri and Aeromonas salmonicida subsp. salmonicida. From 369 obtained isolates, 69 were selected after initial evaluation. Afterwards, additional screening was carried out by spot-on-lawn assay to finally select twelve isolates; four were identified as Pediococcus acidilactici, seven as Weissella cibaria, and one as Weissella paramesenteroides by matrix assisted laser desorption/ionization, time-of-flight mass spectrometry (MALDI-TOF MS). Selected bacteria were used to obtain postbiotic products to test their antagonistic activity through coculture challenge and broth microdilution assays. The influence of incubation time prior to postbiotic production on antagonistic behavior was also recorded. Two isolates identified as W. cibaria were able to significantly reduce (p < 0.05) A. salmonicida subsp. salmonicida's growth in the coculture challenge up to 4.49 ± 0.05 Log CFU/mL, and even though the reduction in Y. ruckeri was not as effective, some inhibition on the pathogen's growth was reported; at the same time, most of the postbiotic products obtained showed more antibacterial activity when obtained from broth cultures incubated for 72 h. Based on the results obtained, the preliminary identification of the isolates that expressed the highest inhibitory activity was confirmed by partial sequencing as W. cibaria. Through our study, it can be concluded that postbiotics produced by these strains are useful to inhibit the growth of the pathogens and could, thereby, be applicable in further research to develop suitable tools as feed additives for disease control and prevention in aquaculture.

Effects of two host-associated probiotics Bacillus mojavensis B191 and Bacillus subtilis MRS11 on growth performance, intestinal morphology, expression of immune-related genes and disease resistance of Nile tilapia (Oreochromis niloticus) against Streptococcusiniae

The intensification and diversification of production systems have increased the incidence of diseases, which are usually treated with antibiotics. However, its use should be restricted due to the increasing prevalence of antibiotic-resistant bacteria. Probiotics represent therefore an alternative environmentally friendly strategy for improving growth and disease resistance in aquaculture. Considering that host-derived probiotics may offer greater advantages than those from other environments in terms of safety and efficacy, two potential host-associated probiotic strains (Bacillus mojavensis B191 and Bacillus subtilis MRS11) were used in the present study, which were previously isolated from intestinal mucus of Nile tilapia (Oreochromis niloticus). This study was conducted to assess the effects of dietary administration of two Bacillus strains on growth performance, intestinal morphology, immunity, and disease resistance of Nile tilapia. A total of 375 fish were randomly divided into five groups in triplicate. Nile tilapia were fed a basal diet (control group) or a basal diet supplemented with Bacillus mojavensis B191 (BM) or Bacillus subtilis MRS11 (BS) spores at different concentrations of 1 × 10⁶ (BM6 and BS6, respectively) and 1 × 10⁸ (BM8 and BS8, respectively) CFU/g of feed for 60 days. Moreover, the survival rate of tilapia upon challenge with Streptococcus iniae was determined following the feeding trial. After the feeding trial, the growth performances were significantly improved in all probiotic-fed groups, with the BS8 group being the highest. Light and electron microscopy observations revealed elevated goblet cells, intestinal villus length (except BM8), microvilli length, microvilli density, and perimeter ratio increase in the intestine of all probiotic-fed groups compared with the control group. Regarding the expression analysis, HSP70 gene was only up-regulated in the BM8 group and a general trend of up-regulation of some immune-related cytokines (TGF-β, IL-10, TNF-α and IL-1β) was observed in all probiotic-fed groups. Likewise, the best protection against Streptococcus iniae was observed in the BS8 group, followed by BS6, BM6 and BM8 groups. Altogether, dietary probiotic supplementation with BS8 and BM6 may improve growth performance, intestinal morphology, immunity, and disease resistance in Nile tilapia.

Spray Drying Encapsulation of Pediococcus acidilactici at Different Inlet Air Temperatures and Wall Material Ratios

Pediococcus acidilactici has gained research and commercial interest due to its outstanding probiotic properties, yet its survival during storage and consumption requires improvement. This study aims to enhance P. acidilactici survival using spray drying encapsulation. Different inlet air temperatures (120 °C, 150 °C, and 170 °C) and whey protein isolate (WPI):gum arabic (GA) ratios (1:1, 3:1, 1:3) were tested. Cell viability was significantly (p < 0.05) affected by the inlet temperature but not the WPI:GA ratio. Increasing the inlet temperature to 170 °C significantly decreased P. acidilactici viability by 1.36 log cycles, from 8.61 log CFU/g to 7.25 log CFU/g. The inlet temperature of 150 °C resulted in a powder yield (63.12%) higher than at 120 °C (58.97%), as well as significantly (p < 0.05) lower moisture content (5.71%) and water activity (aw 0.21). Viable cell counts in all encapsulated P. acidilactici were maintained at 5.24−6.75 log CFU/g after gastrointestinal tract (GIT) simulation, with WPI:GA of 3:1 and inlet temperature 150 °C having the smallest log reduction (0.3 log cycles). All samples containing different WPI:GA ratios maintained sufficient viability (>7 log CFU/g) during the first three weeks of storage at 25 °C. These results could provide insights for further developing P. acidilactici as commercial probiotic products.

Probiotic effects of Pseudoalteromonas ruthenica: Antibacterial, immune stimulation and modulation of gut microbiota composition

This study aimed to characterise and evaluate the probiotic properties of a newly isolated marine bacterium, strain S6031. The isolated strain was identified as Pseudoalteromonas ruthenica. In vivo experiments were conducted with P. ruthenica-immersed larvae and P. ruthenica-enriched Artemia fed to adult zebrafish. Disease tolerance of larval zebrafish against Edwardsiella piscicida was demonstrated by 66.34% cumulative per cent survival (CPS) in the P. ruthenica-exposed group, which was higher than the CPS of the control (46.67%) at 72 h post challenge (hpc). Heat-stressed larvae had 55% CPS in the P. ruthenica-immersed group, while the control had 30% CPS at 60 hpc. Immune-stress response gene transcripts (muc5.1, muc5.2, muc5.3, alpi2, alpi3, hsp70, and hsp90a) were induced, while pro-inflammatory genes (tnfα, il1b, and il6) were downregulated in P. ruthenica-immersed larvae compared to the control. This trend was confirmed by low pro-inflammatory and high stress-responsive protein expression levels in P. ruthenica-exposed larvae. Adult zebrafish had higher CPS (27.2%) in the P. ruthenica-fed group than the control (9.52%) upon E. piscicida challenge, suggesting increased disease tolerance. Histological analysis demonstrated modulation of goblet cell density and average villus height in the P. ruthenica-supplemented group. Metagenomics analysis clearly indicated modulation of alpha diversity indices and the relative abundance of Proteobacteria in the P. ruthenica-supplemented zebrafish gut. Furthermore, increased Firmicutes colonisation and reduced Bacteroidetes abundance in the gut were observed upon P. ruthenica supplementation. Additionally, this study confirmed the concentration-dependent increase of colony dispersion and macrophage uptake upon mucin treatment. In summary, P. ruthenica possesses remarkable functional properties as a probiotic that enhances host defence against diseases and thermal stress.

Dietary supplementation of two indigenous Bacillus spp on the intestinal morphology, intestinal immune barrier and intestinal microbial diversity of Rhynchocypris lagowskii

This study evaluated the effects of dietary administration of two indigenous Bacillus (A: basal control diet; B: 0.15 g/kg of Bacillus subtilis; C: 0.1 g/kg of Bacillus subtilis and 0.05 g/kg of Bacillus licheniformis; D: 0.05 g/kg of Bacillus subtilis and 0.1 g/kg of Bacillus licheniformis; E: 0.15 g/kg of Bacillus licheniformis) on the digestive enzyme activities, intestinal morphology, intestinal immune and barrier-related genes relative expression levels, and intestinal flora of Rhynchocypris lagowskii. The results showed that the fold height, lamina propria width, and muscle layer thickness of midgut and hindgut in group C were significantly higher than that of group A (P < 0.05). The activities of protease, amylase, and lipase in group C were significantly higher than those of group A (P < 0.05). The relative expression levels of IL-1β and IL-8 in the intestine of group C were significantly downregulated, and the relative expression levels of IL-10 and TGF-β were significantly upregulated (P < 0.05). The relative expression levels of Claudin-2 in group A significantly increased and the relative expression levels of Claudin-4 in group A significantly reduced compared with other groups (P < 0.05). The relative expression levels of ZO-1 in groups C and D were significantly higher than those of other groups (P < 0.05). The Bacillus in the intestine of group C has the highest relative abundance among all groups. Overall, it can generally be concluded that dietary supplementation of indigenous Bacillus subtilis and Bacillus licheniformis (group C) can improve the intestinal morphology, digestion, and absorption enzyme activities, enhance intestinal mucosal immunity and barrier function, and maintain the intestinal microbial balance of R. lagowskii.

Gut microbiome modulation mediated by probiotics: Positive impact on growth and health status of Labeo rohita

The current study was targeted to determine the effect of probiotics on the growth, physiology, and gut microbiology of Labeo rohita fingerlings. One hundred and twenty fishes were divided into four dietary groups, each in triplicate for a feeding trial of 90 days. These treatments included T0 (control, basal diet) used as the reference, and three probiotic-supplemented diets represented as Tbc (Bacillus cereus), Tgc (Geotrichum candidum), and Tmc (B. cereus and G. candidum). The probiotics were supplemented at a level of 1 × 109 CFU/g feed. Fishes nurtured on probiotic-added diet showed significantly high physiological improvement (p < 0.05) in terms of growth, feed utilization capacity, hematological profile, and digestive enzymes as compared to control. The fish were subjected to a challenge test after a 90-day feeding trial. The Tmc exhibited maximum fish growth when challenged by Staphylococcus aureus and showed fish survival when compared to control, in which fish mortality was examined. Fish gut microbial composition was modulated by probiotic treatments, especially in Tgc and Tmc as compared to control. The absence of opportunistic pathogens such as Staphylococcus saprophyticus and Sporobolomyces lactosus and detection of lower levels of Trichosporon and Cryptococcus in treated groups indicate the gut modulation driven by applied probiotics. The G. candidum QAUGC01 was retrieved in yeast metagenomics data, which might be due to the production of polyamines by them that facilitated adherence and consequent persistence. In conclusion, it can be suggested that the probiotic-supplemented diet could enhance fish growth and feed efficiency through community modulation and digestive enzymes, which could be a milestone in local aquaculture.

Assessing the effect of probiotics on tilapia lake virus-infected tilapia: Transmission and immune response

Probiotics have been used to alleviate disease transmission in aquaculture. However, there are limited studies on probiotic use in modulating tilapia lake virus (TiLV). We assessed commercially available probiotic supplements used in TiLV-infected tilapia and performed mortality and cohabitation assays. We developed a mechanistic approach to predict dose-response interactions of probiotic effects on mortality and immune gene response. We used a susceptible-infected-mortality disease model to assess key epidemiological parameters such as transmission rate and basic reproduction number (R₀ ) based on our viral load dynamic data. We found that the most marked benefits of probiotics are significantly associated with immune system enhancements (~30%) and reductions in disease transmission (~80%) and R₀ (~70%) in tilapia populations, resulting in a higher tolerance of farming densities (~400 fold) in aquaculture. These findings provide early insights as to how probiotic use-related factors may influence TiLV transmission and the immune responses in TiLV-infected tilapia. Our study facilitates understanding the mode of action of probiotics in disease containment and predicting better probiotic dosages in diet and supplements to achieve the optimal culturing conditions. Overall, our analysis assures that further study of rationally designed and targeted probiotics, or mechanistic modelling is warranted on the basis of promising early data of this approach.

Recent Discoveries on Marine Organism Immunomodulatory Activities

Marine organisms have been shown to be a valuable source for biologically active compounds for the prevention and treatment of cancer, inflammation, immune system diseases, and other pathologies. The advantage of studying organisms collected in the marine environment lies in their great biodiversity and in the variety of chemical structures of marine natural products. Various studies have focused on marine organism compounds with potential pharmaceutical applications, for instance, as immunomodulators, to treat cancer and immune-mediated diseases. Modulation of the immune system is defined as any change in the immune response that can result in the induction, expression, amplification, or inhibition of any phase of the immune response. Studies very often focus on the effects of marine-derived compounds on macrophages, as well as lymphocytes, by analyzing the release of mediators (cytokines) by using the immunological assay enzyme-linked immunosorbent assay (ELISA), Western blot, immunofluorescence, and real-time PCR. The main sources are fungi, bacteria, microalgae, macroalgae, sponges, mollusks, corals, and fishes. This review is focused on the marine-derived molecules discovered in the last three years as potential immunomodulatory drugs.

Effect of dietary supplementation of Cetobacterium somerae XMX-1 fermentation product on gut and liver health and resistance against bacterial infection of the genetically improved farmed tilapia (GIFT, Oreochromis niloticus)

The purpose of this study was to evaluate the effects of Cetobacterium somerae XMX-1 fermentation product on gut and liver health and resistance against bacterial infection in genetically improved farmed tilapia (GIFT, Oreochromis niloticus). Fingerling GIFTs (n = 120; initial weight 1.33 ± 0.00 g) were randomly assigned to twelve 90-L tanks (four tanks per diet, 10 fish per tank) with three groups: control group (basal high fat diet), 1% XMX-1 group and 2% XMX-1 group (basal diet supplemented with 10 and 20 g XMX-1/kg feed respectively). After 49 days feeding trial, the growth performance and gut and liver health parameters of tilapia were evaluated. Also the gut microbiota and virome were detected by sequencing. 2% XMX-1 fermentation product had no effect on growth performance. For gut health, the expression of hypoxia-inducible factor-lα (Hif-1α) tend to increase in 1% XMX-1 group (P = 0.053). The expression of intestinal interleukin-6 (IL-6) and tumor growth factor β (TGF-β) was significantly down-regulated in 1% and 2% XMX-1 groups (P < 0.05), and the intestinal expression of interleukin-1β (IL-1β) had a trend to decrease (P = 0.08) in 1% XMX-1 group versus control. 1% and 2% XMX-1 groups also increased the intestinal expression of tight junction genes Claudin (P = 0.06 and 0.07, respectively). For liver health, XMX-1 fermentation product significantly decreased liver TAG (P < 0.05). Furthermore, the hepatic expression of lipid synthesis gene fatty acid synthase (FAS) was significantly decreased and the expression of lipid catabolism related-gene uncoupling protein 2 (UCP2) was significantly increased in 1% XMX-1 and 2% XMX-1 groups (P < 0.01). And the hepatic expression of IL-1β and IL-6 significantly decreased in 1% XMX-1 and 2% XMX-1 groups (P < 0.05). XMX-1 fermentation product increased the abundance of Fusobacteria in the gut microbiota and 2% XMX-1 group led to alteration in the virome composition at family level. Lastly, the time of tilapia death post Aeromoans challenge was delayed in 1% XMX-1 and 2% XMX-1 groups compared with control. To sum up, our results show that the dietary supplementation of XMX-1 fermentation product can improve the gut and liver health as well as the resistance against pathogenic bacteria of tilapia.

The synergistic effects of plant polysaccharide and Pediococcus acidilactici as a synbiotic additive on growth, antioxidant status, immune response, and resistance of Nile tilapia (Oreochromis niloticus) against Aeromonas hydrophila

This study evaluated the growth performance, immune responses, and disease resistance of Nile tilapia upon pistachio hulls derived polysaccharide (PHDP) and Pediococcus acidilactici (PA) separately or as synbiotic. Fish received four types of diets: T1, control; T2, PHDP (0.1%); T3, PA (0.2%); T4, PHDP (0.1%) +PA (0.2%) for 56 days. The results showed that final weight and weight gain were markedly higher in fish fed T4 diet than that given T1 and T2 diets (P ≤ 0.05). In addition, a significantly greater specific growth rate was obtained by the T4 diet compared to the control. Fish survival was significantly improved in all supplemented diets compared to the control. On the other hand, the activities of lipase, protease, and amylase showed significant increases in the T4 group compared with other feeding groups. The total leucocytes and lymphocytes proportion significantly elevated in T3 and T4 than remaining groups (P ≤ 0.05). Further, fish fed T3 diet presented significantly higher serum total protein, total immunoglobulin, lysozyme activity (LYZ), alternative complement activity (ACH50), and alkaline phosphatase activity compared to fish fed T1 and T2 diets, while the mentioned indices were found significantly highest in T4 group than others. Fish received T3 and T4 diets had higher skin mucus LYZ and ACH50 than those fed T1 and T2 diets (P ≤ 0.05). The malondialdehyde levels were significantly declined in T3 and T4 when compared to the control. Fish fed T3 and T4 diets demonstrated significantly enhanced superoxide dismutase, catalase, and glutathione peroxidase activities compared to the control. The intestinal propionic acid significantly increased by T2 and T4 diets, while the highest levels of acetic acid detected in fish given T4 diet. The expression levels of tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), and interleukin 10 (IL-10) were significantly affected by T3 and T4 supplements. The efficacy of T4 diet against Aeromonas hydrophila infection was documented by a significantly lower mortality rate. In conclusion, the combination of PHDP and PA presented promising results as a synbiotic feed additive for Nile tilapia.

A Novel Pseudoalteromonas xiamenensis Marine Isolate as a Potential Probiotic: Anti-Inflammatory and Innate Immune Modulatory Effects against Thermal and Pathogenic Stresses

A marine bacterial strain was isolated from seawater and characterized for it beneficial probiotic effects using zebrafish as a model system. The strain was identified by morphological, physiological, biochemical, and phylogenetic analyses. The strain was most closely related to Pseudoalteromonas xiamenensis Y2, with 99.66% similarity; thus, we named it Pseudoalteromonas xiamenensis S1131. Improvement of host disease tolerance for the P. xiamenensis isolate was adapted in a zebrafish model using Edwardsiella piscicida challenge. The larvae were pre-exposed to P. xiamenensis prior to E. piscicida challenge, resulting in a 73.3% survival rate compared to a 46.6% survival for the control. The treated larvae tolerated elevated temperatures at 38 °C, with 85% survival, compared to 60% survival for the control. Assessment of immunomodulatory responses at the mRNA level demonstrated the suppression of pro-inflammatory markers tnfα and il6, and upregulation of heat shock protein hsp90 and mucin genes. The same effect was corroborated by immunoblot analysis, revealing significant inhibition of Tnfα and an enhanced expression of the Hsp90 protein. The antibacterial activity of P. xiamenensis may be related to mucin overexpression, which can suppress bacterial biofilm formation and enhance macrophage uptake. This phenomenon was evaluated using nonstimulated macrophage RAW264.7 cells. Further studies may be warranted to elucidate a complete profile of the probiotic effects, to expand the potential applications of the present P. xiamenensis isolate.

Lead impaired immune function and tissue integrity in yellow catfish (Peltobargus fulvidraco) by mediating oxidative stress, inflammatory response and apoptosis

Lead (Pb) widely exists in the water environment and has severe toxic effects on aquatic organisms. The yellow catfish (Pelteobagrus fulvidraco) is one of the most important commercial species in China, and moreover, its natural populations are declining with the degradation of environmental water quality. However, little is known about the toxic effects of Pb on its immune organs. This study was performed to determine waterborne Pb exposure on bioaccumulation, histomorphology, antioxidant status, apoptotic and immune response in the head kidney and spleen of yellow catfish. Experimental fish were randomly allocated into twelve tanks (3 tanks per group), and the Pb concentrations of the four groups were 0, 5, 50, and 500 μg/L, respectively. The results reflected that the Pb bioaccumulation of the head kidney and spleen increased with increasing Pb exposure dose and time. Severe histological alterations in the head kidney and spleen were observed at concentration 500 ug/L. With increasing Pb exposure concentrations, the plasma activity of superoxide dismutase (SOD) and catalase (CAT) significantly increased after exposure 7 days and 14 days, and the levels significantly decreased after exposure 28 days. The change trend of glutathione (GSH) levels was opposite to that of SOD and CAT at corresponding exposure time. The plasma malondialdehyde (MDA) levels together with the activities of plasma alkaline phosphatase (AKP) and acid phosphatase (ACP) increased significantly with the increasing Pb concentrations. In contrast, the levels of lysozyme (LYZ), complement 3 (C3) and immunoglobulin M (IgM) decreased significantly with increasing Pb concentrations. Moreover, Pb exposure induced transcriptional upregulation of heat shock protein 70 (hsp70), metallothionein (mt), sod, cat, interleukin-10 (il-10), transforming growth factor-β (tgf-β), and tumor necrosis factor-α (tnf-α), bcl-2-associated X protein (bax), and cysteinyl aspartate specific proteinase -9 (caspase-9), genes in the head kidney and spleen tissues, while downregulating the levels of the lyz, c3, igm and B-cell lymphoma-2 (bcl-2) genes. Our data provide evidence that Pb impaired immune function and tissue integrity in yellow catfish through oxidative stress, inflammatory and apoptosis, and the results can serve as reference data to better protect water environments from Pb eco-toxicants.

Autochthonous Probiotics Alleviate the Adverse Effects of Dietary Histamine in Juvenile Grouper (Epinephelus coioides)

High dose (0.3%) of dietary histamine can cause adverse effects on growth performance, innate immunity, and gut health in juvenile grouper (Epinephelus coioides). In the present study, three autochthonous probiotics (Bacillus pumilus SE5, Psychrobacter sp. SE6, and Bacillus clausii DE5) were supplemented separately to diets containing 0.3% of histamine and their effects on growth performance, innate immunity, and gut health of grouper (E. coioides) were evaluated in a 56-day feeding trial. The results showed considerable increase in weight gain, specific growth rate, hepatosomatic index, and decreased feed conversion rate in groupers fed with probiotic-supplemented diets. Supplementation of autochthonous probiotics has improved antioxidant capacity and innate immunity of E. coioides by measuring correlative parameters, such as total antioxidant capacity, superoxide dismutase activity, malondialdehyde content, and so on. Additionally, dietary probiotics have significantly reduced the levels of serum interleukin-1β (at days 28 and 56), fatty acid-binding protein 2, and intestinal trefoil factor (at day 28), and promoted intestinal integrity following remarkably increased muscle thickness and mucosal fold height at day 56, especially in grouper fed with B. pumilus SE5 containing diet (P < 0.05). On day 56, the gut microbial composition of E. coioides was positively shaped by autochthonous probiotics, the relative abundance of potentially pathogenic Photobacterium decreased while beneficial Lactobacillus increased in fish fed with probiotic strains, especially with B. pumilus SE5 and B. clausii DE5. These results suggest that among the three autochthonous probiotic strains tested, B. pumilus SE5 is showing better efficiency in alleviating the adverse effects of (high levels) dietary histamine by decreasing the expression of inflammatory markers and by improving the growth, innate immunity, and gut health of juvenile grouper E. coioides.

Updating the Role of Probiotics, Prebiotics, and Synbiotics for Tilapia Aquaculture as Leading Candidates for Food Sustainability: a Review

Tilapia production has significantly increased over the past few years due to the adoption of semi-intensive and intensive aquaculture technologies. However, these farming systems have subjected the fish to stressful conditions that suppress their immunity, hence exposing them to various pathogens. The application of antibiotics and therapeutics to enhance disease resistance, survival, and growth performance in aquaculture has been recently banned due to the emergence of antibiotic-resistant bacteria that pose a serious threat to the environment and consumers of aquatic organisms. Hence, the need for an alternative approach based on sustainable farming practices is warranted. Probiotic, prebiotic, and synbiotic use in tilapia production is considered a viable, safe, and environmentally friendly alternative that enhances growth performance, feed utilization, immunity, disease resistance, and fish survival against pathogens and environmental stress. Their inclusion in fish diets and or rearing water improves the general wellbeing of fish. Hence, this review aims at presenting research findings from the use of probiotics, prebiotics, and synbiotics and their effect on survival, growth, growth performance, gut morphology, microbial abundance, enzyme production, immunity, and disease resistance in tilapia aquaculture, while highlighting several hematological, blood biochemical parameters, and omics techniques that have been used to assess fish health. Furthermore, gaps in existing knowledge are addressed and future research studies have been recommended.

The functionality of probiotics in aquaculture: An overview

Probiotics are live beneficial bacteria introduced into the gastrointestinal tract through food or water, promoting good health by enhancing the internal microbial balance. Probiotic microbes produce bacteriocins, siderophores, lysozymes, proteases, and hydrogen peroxides, inhibiting the growth of harmful pathogens. Such beneficial bacteria also produce many enzymes such as amylase enzyme by Aeromonas spp., Bacillus subtilis, Bacteridaceae, Clostridium spp., Lactobacillus plantarum, and Staphylococcus sp., and protease and cellulase enzymes by B. subtilis, L. plantarum, and Staphylococcus sp. In aquaculture, probiotics confer several benefits and play important roles in improving growth performances, disease resistance, immunity, health status, intestinal epithelial barrier integrity, gut microbiome, and water quality. In addition, the practical application of probiotics in aquaculture diets could minimize antibiotic side effects. Promoting these feed additives for fish would help to improve their productive performance and feed utilization and, therefore, boost fish production and safeguard human health. This review provides updated information regarding definitions, sources of bacterial probiotics, probiotic use in fish diets against pathogenic bacteria, mechanisms of action, beneficial aspects, and potential applications of probiotics in fish. It is anticipated that these will be of significant value for nutritionists, agricultural engineers, researchers, pharmacists, scientists, pharmaceutical industries, and veterinarians.

Breeding Strategy Shapes the Composition of Bacterial Communities in Female Nile Tilapia Reared in a Recirculating Aquaculture System

In industrial animal production, breeding strategies are essential to produce offspring of better quality and vitality. It is also known that host microbiome has a bearing on its health. Here, we report for the first time the influence of crossbreeding strategy, inbreeding or outbreeding, on the buccal and intestinal bacterial communities in female Nile tilapia (Oreochromis niloticus). Crossbreeding was performed within a family and between different fish families to obtain the inbred and outbred study groups, respectively. The genetic relationship and structure analysis revealed significant genetic differentiation between the inbred and outbred groups. We also employed a 16S rRNA gene sequencing technique to understand the significant differences between the diversities of the bacterial communities of the inbred and outbred groups. The core microbiota composition in the mouth and the intestine was not affected by the crossbreeding strategy but their abundance varied between the two groups. Furthermore, opportunistic bacteria were abundant in the buccal cavity and intestine of the outbred group, whereas beneficial bacteria were abundant in the intestine of the inbred group. The present study indicates that crossbreeding can influence the abundance of beneficial bacteria, core microbiome and the inter-individual variation in the microbiome.

Probiotics-Live Biotherapeutics: a Story of Success, Limitations, and Future Prospects-Not Only for Humans

In livestock production, lactic acid bacteria (LAB) represent the most widespread microorganisms used as probiotics. For such critical use, these bacteria must be correctly identified and characterized to ensure their safety and efficiency. Recently, probiotics have become highly recognized as supplements for humans and in particular for animals because of their beneficial outcome on health improvement and well-being maintenance. Various factors, encompassing dietary and management constraints, have been demonstrated to tremendously influence the structure, composition, and activities of gut microbial communities in farm animals. Previous investigations reported the potential of probiotics in animal diets and nutrition. But a high rate of inconsistency in the efficiency of probiotics has been reported. This may be due, in a major part, to the dynamics of the gastrointestinal microbial communities. Under stressing surroundings, the direct-fed microbials may play a key role as the salient limiting factor of the severity of the dysbiosis caused by disruption of the normal intestinal balance. Probiotics are live microorganisms, which confer health benefits on the host by positively modifying the intestinal microflora. Thus, the aim of this review is to summarize and to highlight the positive influence of probiotics and potential probiotic microbe supplementation in animal feed with mention of several limitations.

The mutated Bacillus amyloliquefaciens strain shows high resistance to Aeromonas hydrophila and Aeromonas veronii in grass carp

Bacillus amyloliquefaciens X030 (BaX030) has broad-spectrum antibacterial activity against the fish pathogens Aeromonas hydrophila and Aeromonas veronii. To improve its antibacterial effect, BaX030 was subjected to compound mutagenesis of atmospheric and room temperature plasma (ARTP) and nitrosoguanidine (NTG). The results showed that, compared with the original strain, the production of macrolactin A and oxydifficidin in mutated strain N-11 increased to 39 % and 268 %, respectively. The re-sequencing analysis suggested that there were SNPs and InDels in the gene clusters focused on the sucrose utilization pathway, glycolysis pathway and fatty acid synthesis pathway. Scanning electron microscopy revealed that strain N-11 became thin and long. The qRT-PCR results indicated that the expression of immune factors in the liver or kidney tissue of grass carp increased after feeding with N-11. H&E staining and protection experiments also showed that the mortality and surface symptoms of grass carp infected by the two pathogens were significantly reduced. The study identified a probiotic strain with potential application value in aquaculture production and provided a new strategy for the discovery of new strains with higher antibacterial biological activity.

Gut probiotic bacteria of Barbonymus gonionotus improve growth, hematological parameters and reproductive performances of the host

This study aimed to isolate and identify probiotic bacteria from the gut of Barbonymus gonionotus and evaluate their effects on growth, hematological parameters, and breeding performances of the host. Five probiotic bacteria viz. Enterococcus xiangfangensis (GFB-1), Pseudomonas stutzeri (GFB-2), Bacillus subtilis (GFB-3), Citrobacter freundii (GFB-4), and P. aeruginosa (GFB-5) were isolated and identified using 16S rRNA gene sequencing. Application of a consortium of probiotic strains (1-3 × 1.35 × 109 CFU kg-1) or individual strain such as GFB-1 (1.62 × 109 CFU kg-1), GFB-2 (1.43 × 109 CFU kg-1), GFB-3 (1.06 × 109 CFU kg-1), GFB-4 (1.5 × 109 CFU kg-1) or GFB-5 (1.43 × 109 CFU kg-1feed) through feed significantly improved growth, histological and hematological parameters and reproductive performances of B. gonionotus compared to untreated control. Moreover, the application of these probiotics significantly increased gut lactic acid bacteria and activities of digestive enzymes but did not show any antibiotic resistance nor any cytotoxicity in vitro. The highest beneficial effects on treated fishes were recorded by the application of GFB-1, GFB-2, GFB-3, and a consortium of these bacteria (T2). This is the first report of the improvement of growth and health of B. gonionotus fishes by its gut bacteria.

Salmon gut microbiota correlates with disease infection status: potential for monitoring health in farmed animals

BACKGROUND

Infectious diseases cause significant production losses in aquaculture every year. Since the gut microbiota plays an essential role in regulating the host immune system, health and physiology, altered gut microbiota compositions are often associated with a diseased status. However, few studies have examined the association between disease severity and degree of gut dysbiosis, especially when the gut is not the site of the primary infection. Moreover, there is a lack of knowledge on whether bath treatment with formalin, a disinfectant commonly used in aquaculture to treat external infections, might affect the gut microbiome as a consequence of formalin ingestion. Here we investigate, through 16S rRNA gene metabarcoding, changes in the distal gut microbiota composition of a captive-reared cohort of 80 Atlantic salmon (Salmo salar L.), in consequence of an external bacterial skin infection due to a natural outbreak and subsequent formalin treatment.

RESULTS

We identified Tenacibaculum dicentrarchi as the causative disease pathogen and we show that the distal gut of diseased salmon presented a different composition from that of healthy individuals. A new, yet undescribed, Mycoplasma genus characterized the gut of healthy salmon, while in the sick fish we observed an increase in terms of relative abundance of Aliivibrio sp., a strain regarded as opportunistic. We also noticed a positive correlation between fish weight and Mycoplasma sp. relative abundance, potentially indicating a beneficial effect for its host. Moreover, we observed that the gut microbiota of fish treated with formalin was more similar to those of sick fish than healthy ones.

CONCLUSIONS

We conclude that external Tenacibaculum infections have the potential of indirectly affecting the host gut microbiota. As such, treatment optimization procedures should account for that. Formalin treatment is not an optimal solution from a holistic perspective, since we observe an altered gut microbiota in the treated fish. We suggest its coupling with a probiotic treatment aimed at re-establishing a healthy community. Lastly, we have observed a positive correlation of Mycoplasma sp. with salmon health and weight, therefore we encourage further investigations towards its potential utilization as a biomarker for monitoring health in salmon and potentially other farmed fish species.

Multi-Strain Probiotics: Synergy among Isolates Enhances Biological Activities

The use of probiotics for health benefits is becoming popular because of the quest for safer products with protective and therapeutic effects against diseases and infectious agents. The emergence and spread of antimicrobial resistance among pathogens had prompted restrictions over the non-therapeutic use of antibiotics for prophylaxis and growth promotion, especially in animal husbandry. While single-strain probiotics are beneficial to health, multi-strain probiotics might be more helpful because of synergy and additive effects among the individual isolates. This article documents the mechanisms by which multi-strain probiotics exert their effects in managing infectious and non-infectious diseases, inhibiting antibiotic-resistant pathogens and health improvement. The administration of multi-strain probiotics was revealed to effectively alleviate bowel tract conditions, such as irritable bowel syndrome, inhibition of pathogens and modulation of the immune system and gut microbiota. Finally, while most of the current research focuses on comparing the effects of multi-strain and single-strain probiotics, there is a dearth of information on the molecular mechanisms of synergy among multi-strain probiotics isolates. This forms a basis for future research in the development of multi-strain probiotics for enhanced health benefits.

Isolation and Characterization of a Bacillus velezensis D-18 Strain, as a Potential Probiotic in European Seabass Aquaculture

Within the food-producing sectors, aquaculture is the one that has developed the greatest growth in recent decades, currently representing almost 50% of the world's edible fish. The diseases can affect the final production in intensive aquaculture; in seabass, aquaculture vibriosis is one of the most important diseases producing huge economical losses in this industry. The usual methodology to solve the problems associated with the bacterial pathology has been the use of antibiotics, with known environmental consequences. This is why probiotic bacteria are proposed as an alternative fight against pathogenic bacteria. The aim of this study was to analyse a strain of Bacillus velezensis D-18 isolated from a wastewater sample collected from a fish farm, for use as probiotics in aquaculture. The strain was evaluated in vitro through various mechanisms of selection, obtaining as results for growth inhibition by co-culture a reduction of 30%; B. velezensis D-18 was able to survive at 1.5-h exposure to 10% seabass bile, and at pH 4, its survival is 5% and reducing by 60% the adhesion capacity of V. anguillarum 507 to the mucus of seabass and in vivo by performing a challenge. Therefore, in conclusion, we consider B. velezensis D-18 isolate from wastewater samples collected from the farms as a good candidate probiotic in the prevention of the infection by Vibrio anguillarum 507 in European seabass after in vitro and biosafety assays.

Changes in rainbow trout (Oncorhynchus mykiss) growth and mucosal immune parameters after dietary administration of grape (Vitis vinifera) seed extract

The effect of dietary grape (Vitis vinifera) seed extract (GSE) on growth performance and mucosal immune parameters in rainbow trout (Oncorhynchus mykiss) fry was studied. Fish (1.3 g mean weight) were randomly distributed in nine tanks (15 fish per tank) and fed diets containing GSE at 0 (control), 100, and 200 mg kg^-1for 60 days. The results showed that growth parameters were enhanced in both treatment groups compared to the control group. Histological examination of fish skin showed higher epidermis thickness, goblet cell density, and volume density in the GSE groups compared to the values of the control group. Furthermore, the villus height, goblet cell density, and intraepithelial lymphocytes were increased in the fish intestine in those fish fed GSE, with respect to control fish. Feeding fish with low dose of GSE (100 mg kg^-1) up-regulated the expression of some immune-relevant genes, including complement component 3 (C3), lysozyme (Lys), omDB-3, interferon gamma (IFN-γ), and tumor necrosis factor-α (TNF-α) in different mucosal tissues. However, feeding fish the high dose of GSE (200 mg kg^-1) mostly enhanced expression of these genes in the skin. Besides, skin mucus of fish fed GSE showed bactericidal activity against Yersinia ruckeri. It was concluded that GSE, especially at 100 mg kg^-1, modulates the growth performance and mucosal immunity of rainbow trout.

Dietary Supplementation of Bacillus sp. SJ-10 and Lactobacillus plantarum KCCM 11322 Combinations Enhance Growth and Cellular and Humoral Immunity in Olive Flounder (Paralichthys olivaceus)

Experiments were conducted to identify different ratios of Bacillus sp. SJ-10 and Lactobacillus plantarum KCCM 11322 mixtures at a concentration of 1 × 10⁸ CFU/g diet; the effects on growth and cellular and humoral immune responses and the characteristics of disease protection in olive flounder (Paralichthys olivaceus). Flounder were divided into six groups and fed control diet D-1 (without Bacillus sp. SJ-10 and L. plantarum KCCM 11322), positive control diets D-2 (Bacillus sp. SJ-10 at 1 × 10⁸ CFU/g feed) and D-3 (L. plantarum KCCM 11322 at 1 × 10⁸ CFU/g feed); or treatment diets D-4 (3:1 Bacillus sp. SJ-10 and L. plantarum KCCM 11322 at 0.75 + 0.25 × 10⁸ CFU/g feed), D-5 (1:1 Bacillus sp. SJ-10 and L. plantarum KCCM 11322 at 0.50 + 0.50 × 10⁸ CFU/g feed), or D-6 (1:3 Bacillus sp. SJ-10 and L. plantarum KCCM 11322 at 0.25 + 0.75 × 10⁸ CFU/g feed) for 8 weeks. Group D-4 demonstrated better growth and feed utilization (P < 0.05) compared with the controls and positive controls. Similar modulation was also observed in respiratory burst for all treatments and in the expression levels of TNF-α, IL-1β, IL-6, and IL-10 in different organs in D-4. D-4 and D-5 increased respiratory burst, superoxide dismutase, lysozyme, and myeloperoxidase activities compared with the controls, and only D-4 increased microvilli length. When challenged with 1 × 10⁸ CFU/mL Streptococcus iniae, the fish in the D-4 and D-5 groups survived up to 14 days, whereas the fish in the other groups reached 100% mortality at 11.50 days. Collectively, a ratio-specific Bacillus sp. SJ-10 and L. plantarum KCCM 11322 mixture (3:1) was associated with elevated growth, innate immunity, and streptococcosis resistance (3:1 and 1:1) compared with the control and single probiotic diets.

Dietary administration of β-1,3/1,6-glucan and Lactobacillus plantarum improves innate immune response and increases the number of intestine immune cells in roach (Rutilus rutilus)

BACKGROUND

The aim of the study has been to compare the effect of dietary supplementation of β-1,3/1,6-glucan, Lactobacillus plantarum bacteria or their mixture on the growth performance, selected parameters of the immune system as well as the liver and intestinal histology of roach. Fish were fed for 14 days with four different diets, each treatment being carried out in triplicate. In control group, fish were fed dry commercial starter feed Aller Performa 2 (Aller Aqua, Denmark). The other experimental fish groups received the same commercial starter feed supplemented with: 1% β-1,3/1,6-glucan (Leiber® Beta-S) in group G; 108 cfu L. plantarum g- 1 in group L; 1% β-1,3/1,6-glucan + 108 cfu L. plantarum g- 1 in group G + L. The stimulating effect of the tested preparations was evaluated once the feeding with commercial feed exclusively was resumed and 2 weeks afterwards.

RESULTS

No effect on the survivability and growth performance of the fish was observed in any of the groups. Supplementation of feed with β-1,3/1,6-glucan improved (P < 0.05) selected parameters of innate humoral immunity and the pinocytotic activity of phagocytes. Increased respiratory burst activity of head kidney phagocytes (RBA) was observed in groups L and G + L (P < 0.05), and the effect persisted for 2 weeks after the commercial feed regime was resumed. An analogous tendency was determined for the killing activity of phagocytes (PKA) of the head kidney with respect to Aeromonas hydrophila, although this effect appeared only during the feed supplementation period. Supplying roach with β-1,3/1,6-glucan, singly or with L. plantarum, had no effect (P > 0.05) on the proliferation of mitogen-activated lymphocytes. However, an increase in the number of CD3-positive cells and goblet cells was noticed in the digestive system of the L group fish (P < 0.05).

CONCLUSIONS

The results show that feeding fish with added L. plantarum and β-1,3/1,6-glucan stimulates the non-specific resistance mechanisms and raises the counts of intestinal immune cells. Synbiotic may help to control serious bacterial diseases and offer an alternative to antibiotics commonly used in fish farming, and its prolonged immunostimulatory effect could increase fish surviving after release to the natural environment.

Effects of dietary Lactobacillus plantarum (KC426951) in biofloc and stagnant-renewal culture systems on growth performance, mucosal parameters, and serum innate responses of Nile tilapia Oreochromis niloticus

Effects of dietary Lactobacillus plantarum (KC426951) on growth and innate responses of Nile tilapia Oreochromis niloticus were evaluated in biofloc technology system and stagnant-renewal culture system (SRCS). The 90-day-long experiment contained four treatments: SRCS without probiotic (T1), SRCS with probiotic (T2), biofloc without probiotic (T3), and biofloc with probiotic (T4). The administration dose of probiotic was 2 × 10⁸ CFU kg^-1 diet. At the end of experiment, the mean final weights, specific growth rates, feed conversion ratios, and total biomass were significantly (P < 0.05) better in BFT treatments, with no significant effect of probiotic on these parameters in both culture systems. Meanwhile, skin mucosal parameters including total protein (TP), lysozyme (LYZ), alkaline phosphatase (ALP), and protease (PRO) activity were significantly enhanced following probiotic supplementation. T4 treatment displayed a significantly higher LYZ and ALP activity in mucus versus other treatments. Also, serum alternative complement activity was significantly heightened in probiotic-supplemented fish. Superoxide dismutase activity in T4 was detected higher than that of SRCS groups. The results of the current study demonstrated the enhancement of some mucosal and serum innate responses of Nile tilapia in both culture systems upon L. plantarum (KC426951) supplementation.

The efficacy of lactic acid bacteria usage in turbot Scophthalmus maximus on intestinal microbiota and expression of the immune related genes

To understand the efficacy of lactic acid bacteria (LAB) as probiotics on the growth, immune response and intestinal microbiota of turbot Scophthalmus maximus, in this study, the Leuconostoc mesenteroides HY2 strain screened from wide caught fish was bath administrated for juvenile turbot with no bacteria administrated as control. The mRNA levels of toll-like receptors 3 (TLR3), interleukin 8 (IL-8) and interferon induced with helicase C domain 1 (IFIH1) in different organs (i.e. intestine, liver, spleen, kidney, brain and skin) were analyzed using RT-PCR technology. The intestinal microbiota was analyzed by 16S rRNA sequencing, in which principal co-ordinates analysis (PCoA) as well as cluster analysis was performed. The results showed that the specific growth rate of turbot in the LAB treatment was significantly higher than those of the control group (P < 0.05). The expression levels of TLR3, IL-8 and IFIH1 were significantly up-regulated in the organs of LAB treatment, except that IL-8 was slightly down-regulated in kidney. A total of 42 phyla in intestinal microbiota were identified. The composition of intestinal microbiota showed significant differences between LAB treatment and the control group. Shannon index in the LAB treatment was significantly increased while Simpson index significantly declined. The PCoA and cluster analysis exhibited significant differences in the composition and abundance between the two groups. Firmicutes, Proteobacteria, Bacteroidetes and Actinobacteria acted as biomarkers which may have effects to promote absorption and/or trigger the immune function. In conclusion, the administration of HY2 strain was capable of improving growth performance of turbot by enhancing immune response and optimizing structure and diversity of intestinal microbiota.

Effects of dietary non-viable Bacillus sp. SJ-10, Lactobacillus plantarum, and their combination on growth, humoral and cellular immunity, and streptococcosis resistance in olive flounder (Paralichthys olivaceus)

Heat-killed (HK) Bacillus sp. SJ-10 (B), HK Lactobacillus plantarum (P), and their combination were dietary supplemented to olive flounder (Paralichthys olivaceus) to quantify the effects on growth, innate immunity, and disease resistance. Four test diets were supplied: a control feed free of HK probiotics, 1 × 10⁸ CFUs g^-1 single treatments of each of HK B (HKB) and HK P (HKP), and an equal proportion of (0.5 HKB + 0.5 HKP) × 10⁸ CFUs g^-1 (HKB_0.5 HKP_0.5). At 8 weeks of completion feeding trail, HKB_0.5 HKP_0.5 significantly (P < .05) improved growth, feed utilization, and nonspecific immune parameters (respiratory burst and superoxide dismutase) compared to the control group. Similarly, serum lysozyme and myeloperoxidase activities were higher in both HKB and HKB_0.5HKP_0.5 groups. The levels of pro-inflammatory cytokine IL-6 in the liver and IL-1β in the liver, kidney, and spleen were also improved in the treatments, but microvilli length was only increased in HKB_0.5HKP_0.5. After Streptococcus iniae 1 × 10⁸ CFUs mL^-1 challenged; HKB and HKB_0.5HKP_0.5 had a higher survival than control and HKP. Overall, dietary administration of synergy HK probiotics elevated growth, cellular and humoral immunity, and streptococcosis resistance in olive flounder.

Large-scale profiling of the proteome and dual transcriptome in Nile tilapia (Oreochromis niloticus) challenged with low- and high-virulence strains of Streptococcus agalactiae

Streptococcus agalactiae is a common pathogen in aquatic animals, especially tilapia, that hinders aquaculture development and leads to serious economic losses. Previously, a S. agalactiae strain named HN016 was identified from infected tilapia, and the attenuated strain YM001 was subsequently obtained by continuous passaging in Tryptic Soy Broth (TSB) medium. YM001 has been demonstrated as a safe vaccine for S. agalactiae infection in tilapia. To understand the molecular bases of the virulence of these two strains, we performed proteomic and transcriptomic analysis to reveal the protein and gene expression changes in the liver and intestine during the infection process. HN016 significantly decreased the contents of white blood cells (WBCs), neutrophils (NEUs), red blood cells (RBCs) and hematocrit (HCT) and increased the levels of total protein (TP), albumin (ALB) and globulin (GLO), while no such significant differences were observed when comparing the control with YM001. During the infection process, pathogenic peptidoglycan hydrolase, CSPA and membrane proteins were significantly differentially expressed between YM001 and HN016. Furthermore, both proteome and transcriptome data showed that the complement and coagulation cascades pathway and the antigen processing and presentation pathway were stimulated in the liver and intestine, respectively, by YM001 infection compared to HN016 infection. The interaction network analysis of key virulence genes from pathogens suggested that CSPA, as a key node, affects the expression of DOLPP1, MIPEP, PA2G4, OCIAD1, G3BP1 and CLIC5 with a positive correlation. The present evidence suggests that during the infection process, CSPA was the key genes contributing to low virulence in YM001.

Dietary supplementation of Geotrichum candidum improves growth, gut microbiota, immune-related gene expression and disease resistance in gibel carp CAS Ⅲ (Carassius auratus gibelio)

Geotrichum candidum is a filamentous fungus mostly used in the dairy industry for cheese ripening and flavoring. The current study was designed to evaluate the potential probiotics effect of dietary supplementation of G. candidum on growth, digestive enzymes activities, gut microbiota and immune-related gene expression and disease resistance in Gibel carp CAS Ⅲ (Carassius auratus gibelio) against A. hydrophila infections. For this purpose, 420 healthy fish (initial body weight: 7.09 ± 0.02g) were randomly divided into 7 feeding groups in triplicates of 20 fish in each tank. Seven isocaloric and isonitrogenous diets were prepared, supplemented with 6 different doses of G. candidum viz; C: 0, T1:10⁶, T2:10⁷, T3:10⁸, T4:10⁹, T5:10¹⁰, T6:10¹¹ CFU/kg diet and fed to fish twice a day for 60 days. Results showed significantly higher weight gain (WG) and feed efficiency (FE) in groups fed 10⁶ and 10⁸ CFU/kg diet compared to the control (P < 0.05). All G. candidum fed groups showed higher intestinal α-amylase activity (P < 0.05) while no difference in lipase and trypsin activity compared to the control group. Before challenge test, gut microbial diversity analysis revealed relatively more abundance of bacteria belonging to phylum Proteobacteria, Actinobacteria, Firmicutes and Bacteriodetes in group fed G. candidum supplemented diet and higher percentage of pathogenic bacteria belonging to order Aeromonadales and Vibrionales in control post-challenge. After challenge test immune response expressed numerically higher survival rate (P > 0.05) and significantly higher (P < 0.05) Respiratory Burst Activity(RBA), Immunoglobulin M level (IgM), Aspartate Transaminase activity (AST) and improved (P > 0.05) lysozyme activity, and Alanine Transaminase activity (ALT) in groups fed 10⁶ and 10⁸ CFU/kg G. candidum supplemented diet. The expression of immune related gene (IL-I β, TNF- α, HSP70 and TLR-2) in liver of the fish were significantly affected (P < 0.05) by supplementation of G. candidum post bacterial challenge. The results showed that G. candidum is a potential probiotic as it could improve feed utilization, immunity and cause no harmful effects on growth of gibel carp at higher supplementation levels. The productive results can be achieved by using the lower dose as 10⁶-10⁸ CFU/kg diet.

Comparative study of host-associated and commercial probiotic effects on serum and mucosal immune parameters, intestinal microbiota, digestive enzymes activity and growth performance of roach (Rutilus rutilus caspicus) fingerlings

The study aimed to isolate host-associated probiotic (HAP) lactic acid bacteria from intestine of adult Caspian roach and compare the efficacy of HAP with a commercially available probiotic strain (Pediococcus acidilactici) on the growth and feed utilisation, digestive enzymes and systemic and mucosal immune system of roach fingerling. The HAP strain isolated from roach intestine was Enterococcus faecium strain CGMCC1.2136. The experiment was a simple completely randomized design and lasted for eight weeks. Two hundred and seventy fish with an average weight of 12 g randomly distributed into nine tanks. The trial consisted of three treatments with three respective replications. During the experimental period, fish received basal diet without any bacterial supplementation (as the control group), basal diet enriched with 10⁸ CFU g^-1 HAP or 10⁷ CFU g^-1 CP. At the end of the experiment, serum immune parameters of those fish fed HAP including alkaline phosphatase activity, total protein content, total immunoglobulin level, lysozyme activity and complement activity (ACH50) were significantly higher that other experimental groups (P < 0.05). Similarly, dietary supplementation of HAP resulted in better mucosal immune parameters in comparison to control group and commercial probiotic administration (P < 0.05). Intestinal heterotrophic bacteria and autochthonous LAB counts of those fish fed HAP were significantly higher than other experimental groups at the end of the experiment as well as 15 days seizing probiotic administrations (P < 0.05). Fish fed with HAP containing diet presented significantly higher amylase, lipase and protease activity in comparison to the CP fed fish and the control group (P < 0.05). Growth indices of those fish fed HAP were significantly higher than other treatments (P < 0.05). The highest carcass protein and ash content along with the lowest body moisture content belonged to those fish received HAP (P < 0.05). In conclusion, the use host-HAP resulted in better immune competence and growth performance and it seems aquaculture sector should probably focus on the development of probiotics isolated from the cultured species instead of using terrestrial probiotics with greatly different requirements and environmental conditions.

Effect of mannan oligosaccharides on the microbiota and productivity parameters of Litopenaeus vannamei shrimp under intensive cultivation in Ecuador

The white leg Litopenaeus vannamei shrimp is of importance to the eastern Pacific fisheries and aquaculture industry but suffer from diseases such as the recently emerged early mortality syndrome. Many bacterial pathogens have been identified but the L. vannamei microbiota is still poorly known. Using a next-generation sequencing (NGS) approach, this work evaluated the impact of the inclusion in the diet of mannan oligosaccharide, (MOS, 0.5% w/w), over the L. vannamei microbiota and production behavior of L. vannamei under intensive cultivation in Ecuador. The MOS supplementation lasted for 60 days, after which the shrimp in the ponds were harvested, and the production data were collected. MOS improved productivity outcomes by increasing shrimp survival by 30%. NGS revealed quantitative differences in the shrimp microbiota between MOS and control conditions. In the treatment with inclusion of dietary MOS, the predominant phylum was Actinobacteria (28%); while the control group was dominated by the phylum Proteobacteria (30%). MOS has also been linked to an increased prevalence of Lactococcus- and Verrucomicrobiaceae-like bacteria. Furthermore, under the treatment of MOS, the prevalence of potential opportunistic pathogens, like Vibrio, Aeromonas, Bergeyella and Shewanella, was negligible. This may be attributable to MOS blocking the adhesion of pathogens to the surfaces of the host tissues. Together, these findings point to the fact that the performance (survival) improvements of the dietary MOS may be linked to the impact on the microbiota, since bacterial lines with pathogenic potential towards shrimps were excluded in the gut.

Modulation of transcriptomic profile in aquatic animals: Probiotics, prebiotics and synbiotics scenarios

Aquaculture and fisheries have provided protein sources for human consumption for a long time, but diseases have induced declines in product benefits and raised concerns, resulting in great losses to these industries in many countries. The overuse of antibiotics for the treatment of diseases has increased the chemical concentrations in culture systems and weakened the natural immunity of aquatic organisms. Concerns regarding the detrimental effects of antibiotics on the environment and human health due to residual antibiotic-related issues encourage the development of reliable, environmental and health safety methods, such as vaccines, probiotics, prebiotics, synbiotics and phytobiotics, for protection against disease and for reducing and possibly eliminating disease occurrence. Immunity has been effectively enhanced by pro-, pre-, and synbiotics, which confer strong protection and reduce the risks associated with stressors and disease outbreaks in culture systems. These agents confer several benefits, including enhancing both host growth and immune responses against pathogens, while sustaining health and environmental stability, and their use is thus widely accepted. Alterations in gene expression in individual cells could serve as an indicator of the immunity and growth rate of aquatic animals after pro-, pre- and synbiotic feeding. This review addresses the potential use of pro, pre- and synbiotics as immunostimulants for improved aquaculture management and environmental health and chronicles the recent insights regarding the application of pro-, pre- and synbiotics with special emphasis on their immunomodulatory and antioxidative responses based on gene expression changes. Furthermore, the current review describes the research gaps and other issues that merit further investigation.

Differential Effects of Dietary Supplementation of Krill Meal, Soybean Meal, Butyrate, and Bactocell® on the Gene Expression of Atlantic Salmon Head Kidney

The head kidney is a key organ that plays a fundamental role in the regulation of the fish immune response and in the maintenance of endocrine homeostasis. Previous studies indicate that the supplementation of exogenous dietary components, such as krill meal (KM), soybean meal (SM), Bactocell® (BA), and butyrate (BU), can have a significant effect on the immune function of the head kidney. The aim of this study was to investigate the differential effect of these four dietary ingredients on the transcriptional profiles of the head kidney of the Atlantic salmon. This study revealed that just a small number of genes were responsive to the feeding regime after a long-term (12 weeks) treatment, and evidenced that the most significant alterations, both in terms of the number of affected genes and magnitude of changes in gene expression, were detectable in the BU- and KM-fed groups compared with controls, while the SM diet had a nearly negligible effect, and BA had no significant effects at all. Most of the differentially expressed genes were involved in the immune response and, in line with data previously obtained from pyloric caeca, major components of the complement system were significantly affected. These alterations were accompanied by an increase in the density of melanomacrophage centers in the KM- and SM-fed group and their reduction in the BU-fed group. While three types of dietary supplements (BU, KM, and SM) were able to produce a significant modulation of some molecular players of the immune system, the butyrate-rich diet was revealed as the one with the most relevant immune-stimulating properties in the head kidney. These preliminary results suggest that further investigations should be aimed towards the elucidation of the potential beneficial effects of butyrate and krill meal supplementation on farmed salmon health and growth performance.

Effects of dietary supplementation with a microalga (Schizochytrium sp.) on the hemato-immunological, and intestinal histological parameters and gut microbiota of Nile tilapia in net cages

Nutritional improvements in intensive aquaculture production systems is necessary for the reduction of stress, maximum utilization of nutritional components, and expression of the genetic potential of fish. The objective of this study was to evaluate the hemato-immunological, and histological parameters and gut microbiota of Nile tilapia fed with the microalga Schizochytrium sp. Males of Nile tilapia were distributed among eight net cages (6 m³), and fed for 105 days with two diets: control (CON), without Schizochytrium sp., and supplemented (SUP), with 1.2% Schizochytrium sp. in the diet. The final weight, mortality, hematocrit, total erythrocyte count (RBC), hemoglobin, hematimetric indices, white blood cell count (WBC), total protein, and serum lysozyme were measured. Alterations in intestinal morphology were evaluated. The gut microbiota was evaluated with next-generation sequencing. No significant differences (p>0.05) were found in the final weight and mortality between diets. Regarding the hematological parameters, a difference (p<0.05) was detected only in RBC, with there being lower values in the SUP, although this group also showed a tendency toward having an increased mean corpuscular hemoglobin level. There were no differences (p>0.05) in total protein and serum lysozyme concentrations or in WBCs between diets, except for lymphocytes, which presented lower values (p<0.05) in the SUP, suggesting immunomodulation by the polyunsaturated fatty acids present in the microalga. There was no difference (p>0.05) in the intestinal morphology between diets. Metagenomic data indicated greater richness (represented by the Chao index) and a higher abundance of the bacterial phylum Firmicutes in the gut microbiota of the tilapia fed with the SUP diet, demonstrating that the digestion and use of the components of the microalga could influence the microbial community. The results indicated that the microalga had modulatory effects on blood cells and the intestinal microbiota, without affecting the structure and integrity of the intestinal villi.

The effect of dietary supplementation with Clostridium butyricum on the growth performance, immunity, intestinal microbiota and disease resistance of tilapia (Oreochromis niloticus)

This study was conducted to assess the effects of dietary Clostridium butyricum on the growth, immunity, intestinal microbiota and disease resistance of tilapia (Oreochromis niloticus). Three hundreds of tilapia (56.21 ± 0.81 g) were divided into 5 groups and fed a diet supplemented with C. butyricum at 0, 1 x 10⁴, 1 x 10⁵, 1 x 10⁶ or 1 x 10⁷ CFU g^-1 diet (denoted as CG, CB1, CB2, CB3 and CB4, respectively) for 56 days. Then 45 fish from each group were intraperitoneally injected with Streptococcus agalactiae, and the mortality was recorded for 14 days. The results showed that dietary C. butyricum significantly improved the specific growth rate (SGR) and feed intake in the CB2 group and decreased the cumulative mortality post-challenge with S. agalactiae in the CB2, CB3 and CB4 groups. The serum total antioxidant capacity and intestinal interleukin receptor-associated kinase-4 gene expression were significantly increased, and serum malondialdehyde content and diamine oxidase activity were significantly decreased in the CB1, CB2, CB3 and CB4 groups. Serum complement 3 and complement 4 concentrations and intestinal gene expression of tumour necrosis factor α, interleukin 8, and myeloid differentiation factor 88 were significantly higher in the CB2, CB3 and CB4 groups. Intestinal toll-like receptor 2 gene expression was significantly upregulated in the CB3 and CB4 groups. Dietary C. butyricum increased the diversity of the intestinal microbiota and the relative abundance of beneficial bacteria (such as Bacillus), and decreased the relative abundance of opportunistic pathogenic bacteria (such as Aeromonas) in the CB2 group. These results revealed that dietary C. butyricum at a suitable dose enhanced growth performance, elevated humoral and intestinal immunity, regulated the intestinal microbial components, and improved disease resistance in tilapia. The optimal dose was 1 x 10⁵ CFU g^-1 diet.

Autochthonous vs allochthonous probiotic strains to Rhamdia quelen

The aim of this study was to obtain an autochthonous probiotic candidate strain from the silver catfish (Rhamdia quelen) intestinal tract, comparing its in vivo performance with an allochthonous probiotic isolated from another fish, Nile tilapia (Oreochromis niloticus), in a growth performance assay. The study was divided in two parts: in vitro and in vivo assay followed by challenge with A. hydrophila. In the in vitro assay, the species-specific isolated strain Lactococcus lactis presented characteristics such as: absence of hemolysis, antagonism to bacterial pathogens isolated from freshwater fish, and considerable speed of duplication. In the in vivo trial, both fish supplemented with autochthonous or allochthonous strains presented an increase the final concentration of lactic acid bacteria in the intestinal tract of the fish after 60 days of dietary supplementation reaching concentrations of 1 × 10⁷ CFU g^-1 and 4 × 10⁷ UFC.g^-1, respectively. In addition, the autochthonous strain increased the mean corpuscular hemoglobin (MCH) of the treated animals, but no significant differences were observed in the other hemato-immunological and zootechnical parameters between treatments. After challenge with Aeromonas hydrophila, only animals that received autochthonous probiotic supplementation showed an increase in the serum total immunoglobulin concentration, but not enough to observe a significant difference in the survival rate between the treatments. Dietary supplementation of the probiotic allochthonous strain did not demonstrate any effects superior to those of the isolated autochthonous strain. Although the autochthonous strain did not present significant improvements in the other parameters evaluated in this study, it was able to inhibit bacterial pathogens in vitro, to increase the final concentration of LAB's and the amount of immunoglobulin after experimental challenge, demonstrating probiotic potential. This study demonstrated for the first time the isolation and in vivo use of an autochthonous probiotic strain isolated from silver catfish, as well as its comparative evaluation with the performance of allochthonous probiotic.

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.

Inhibitory effect of cadmium exposure on digestive activity, antioxidant capacity and immune defense in the intestine of yellow catfish (Pelteobagrus fulvidraco)

Cadmium (Cd) is a toxic heavy metal that can pose a serious threat to aquatic organisms. To evaluate the physiological response and defense mechanism of fish intestine to Cd toxicity, yellow catfish (Pelteobagrus fulvidraco) were exposed to 0 (control), 50 μg/L and 200 μg/L Cd²⁺ for a period of 8 weeks, and then histological changes, digestive activity, antioxidant status and immune responses in the anterior intestine were assessed. After exposure, significant growth retardation and Cd accumulation were observed, and obvious histopathological lesions in the intestine such as increased goblet cells, excessive mucus, vacuolization and thickened lamina propria were detected. Intestinal digestive enzymes activities and related gene expression were inhibited markedly in Cd²⁺ treatments. Furthermore, Cd exposure induced oxidative stress inhibiting antioxidant activity, characterized by an increase in malondialdehyde level as well as the decrease in the activity and transcription level of antioxidant enzymes. In addition, exposure to Cd²⁺ down-regulated the expression of key genes involved in the immune response (lys, c3, tor, tgf-β, il-10, tnf-α and il-8), suggesting immune defense was inhibited. Taken together, the decreased digestive enzyme activity and Cd-induced toxicity stress for antioxidant and immune systems in the intestine might be account for individual growth retardation.

Dietary administration of probiotics modulates non-specific immunity and gut microbiota of Nile tilapia (Oreochromis niloticus) cultured in low input ponds

Poor culture conditions in low input ponds make fish highly susceptible to infectious pathogens which lead to diseases and mortalities yet the effects of probiotics on immunity, gut microbiota and microbiological quality of fish in low input ponds are unknown. Nile tilapia, Oreochromis niloticus fingerlings (40 g) were randomly stocked at 50 fish m⁻³ in 1.25 m³ cages in low input ponds. The fish were fed on diets supplemented with either Saccharomyces cerevisiae (1 × 10¹⁰ CFU g⁻¹) or Bacillus subtilis (1 × 10⁹ CFU g⁻¹) at six levels: Diet 0 (No probiotic); S. cerevisiae at 2 g kg⁻¹ (Diet 1); 4 g kg⁻¹ (Diet 2) and 6 g kg⁻¹ (Diet 3) and B. subtilis at 5 g kg⁻¹ (Diet 4); 10 g kg⁻¹ (Diet 5) and 15 g kg⁻¹ (Diet 6) for 180 days. Results indicate that hemato-immunological parameters (hemoglobin (Hb), red blood cells (RBC), white blood cells (WBC) serum protein, albumin, globulin and lysozyme activity) were significantly higher in fish fed on probiotic treated diets compared to the control (P < 0.05). On the contrary, fish fed on Diet 6 presented significantly similar Hb and globulin values compared to the control (P > 0.05). Additionally, fish fed on probiotic treated diets retained the probiotics in their guts and lower microbial load was realized in their muscle (P < 0.05). In conclusion, B. subtilis and S. cerevisiae supplementation in diets of Nile tilapia reared in low input ponds improves immunity, manipulates gut microbiota and enhances fish flesh quality.