Heat-killed Bacillus sp. SJ-10 probiotic acts as a growth and humoral innate immunity response enhancer in olive flounder (Paralichthys olivaceus)

Preventive and reparative potentials of heat-inactivated and viable commensal Bacillus pumilus SE5 in ameliorating the adverse impacts of high soybean meal in grouper (Epinephelus coioides)

Probiotic Bacillus pumilus SE5, heat-inactivated (HSE5) or active (ASE5), were supplemented to high soybean meal (HSM) (36 %) diet at whole term (0-56 days) and middle term (29-56 days) to investigate the preventing and repairing effects of B. pumilus SE5 in ameliorating the adverse effects of HSM in Epinephelus coioides. The results suggested that the HSM significantly decreased the weight gain rate (WGR), specific growth rate (SGR), and increased the feed conversion rate (FCR) at day 56 (P < 0.05), while HSE5 and ASE5 promoted the growth performance. The HSE5 and ASE5 showed preventive and reparative functions on the antioxidant capacity and serum immunity, with significantly increased the total antioxidant capacity (T-AOC), superoxide dismutase (SOD), glutathione (GSH), glutathione peroxidase (GSH-PX) activities, and reduced malondialdehyde (MDA) level, and increased acid phosphatase (ACP), alkaline phosphatase (AKP), immunoglobulin M (IgM) and complement 3 (C3). The HSM impaired the intestinal health (destroyed the intestinal structure, significantly increased the contents of serum D-lactic acid and diamine oxidase, and reduced the expressions of claudin-3 and occludin), while HSE5 and ASE5 improved them at whole term and middle term. The HSM impaired the intestinal microbiota and reduced its diversity, and the HSE5 or ASE5 improved the intestinal microbiota (especially at whole term). HSE5 and ASE5 improved the intestinal mRNA expressions of anti-inflammatory genes (il-10 and tgf-β1) and reduced the expressions of pro-inflammatory genes (il-1β, il-8, il-12), and promoted the expressions of humoral immune factor-related genes (cd4, igm, mhcII-α) and antimicrobial peptide genes (β-defensin, epinecidin-1 and hepcidin-1), and decreased the expressions of NF-κB/MAPK signaling pathway-related genes (ikk-α, nf-κb, erk-1), and improved the expressions of MAPK signaling pathway-related gene p38-α (P < 0.05). In conclusion, the heat-inactivated and active B. pumilus SE5 effectively prevented and repaired the suppressive effects of soybean meal in E. coioides, which underscored the potential of B. pumilus SE5 as a nutritional intervention agent in HSM diet in aquaculture.

LTA and PGN from Bacillus siamensis can alleviate soybean meal-induced enteritis and microbiota dysbiosis in Lateolabrax maculatus

An eight-week feeding trial was designed to assess which component of commensal Bacillus siamensis LF4 can mitigate SBM-induced enteritis and microbiota dysbiosis in spotted seabass (Lateolabrax maculatus) based on TLRs-MAPKs/NF-кB signaling pathways. Fish continuously fed low SBM (containing 16 % SBM) and high SBM (containing 40 % SBM) diets were used as positive (FM group) and negative (SBM group) control, respectively. After feeding high SBM diet for 28 days, fish were supplemented with B. siamensis LF4-derived whole cell wall (CW), cell wall protein (CWP), lipoteichoic acid (LTA) or peptidoglycan (PGN) until 56 days. The results showed that a high inclusion of SBM in the diet caused enteritis, characterized with significantly (P < 0.05) decreased muscular thickness, villus height, villus width, atrophied and loosely arranged microvillus. Moreover, high SBM inclusion induced an up-regulation of pro-inflammatory cytokines and a down-regulation of occludin, E-cadherin, anti-inflammatory cytokines, apoptosis related genes and antimicrobial peptides. However, dietary supplementation with CW, LTA, and PGN of B. siamensis LF4 could effectively alleviate enteritis caused by a high level of dietary SBM. Additionally, CWP and PGN administration increased beneficial Cetobacterium and decreased pathogenic Plesiomonas and Brevinema, while dietary LTA decreased Plesiomonas and Brevinema, suggesting that CWP, LTA and PGN positively modulated intestinal microbiota in spotted seabass. Furthermore, CW, LTA, and PGN application significantly stimulated TLR2, TLR5 and MyD88 expressions, and inhibited the downstream p38 and NF-κB signaling. Taken together, these results suggest that LTA and PGN from B. siamensis LF4 could alleviate soybean meal-induced enteritis and microbiota dysbiosis in L. maculatus, and p38 MAPK/NF-κB pathways might be involved in those processes.

Effect of dietary heat-killed Lactiplantibacillus plantarum VSG3 on growth, immunity, antioxidant status, and immune-related gene expression in pathogen-aggravated Cyprinus carpio

Heat-killed probiotics offer an alternative approach to enhance growth and disease resistance in farmed fish. In this study, we isolated Lactiplantibacillus plantarum VSG3 from the gut of Labeo rohita to investigate the effects of heat-killed L. plantarum (HK-LP) on the health and growth performance of Cyprinus carpio fingerlings. Different concentrations of HK-LP (0, 50, 100, 200, 300, and 400 mg/kg) were administered to the fish, followed by a challenge with Aeromonas hydrophila after 8 weeks of feeding. Notably, the LP200 group exhibited significantly improved percentage weight gain and specific growth rate, accompanied by the lowest feed conversion ratio. Post-challenge survival rates were considerably enhanced in the LP200 group, reaching 60.65%. Moreover, serum analysis indicated significantly higher levels of total protein and albumin in the LP200 group than in the control group. Although HK-LP had no substantial impact on certain serum parameters (glucose, total cholesterol, cortisol, and alanine aminotransferase), aspartate aminotransferase levels were considerably low in the LP200 group. Intestinal protease and trypsin activities significantly increased in the LP200 group, while no significant changes were observed in lipase and amylase activities post-pathogen challenge. Serum immunological indices, including lysozyme, alternative complement pathway, and phagocytic activity, improved considerably in the LP200 group. Additionally, serum antioxidant enzyme activities (superoxide dismutase [SOD], glutathione peroxidase [GPx], catalase [CAT], and myeloperoxidase) were significantly elevated in the LP200 group, while malondialdehyde level was reduced. Gene expression analysis in liver tissue indicated strong upregulation of antioxidant-related genes (SOD, CAT, nuclear factor erythroid 2 [NFE2]-related factor 2 [Nrf2], Kelch-like ECH-associated protein 1[Keap1]) in the LP100 and LP200 groups. Pro-inflammatory cytokines (IL-1β and TNF-α) were considerably downregulated in the kidneys of the LP200 post-challenged fish, although the anti-inflammatory cytokine IL-10 showed an increased expression. Quadratic regression analysis identified the optimal dietary HK-LP level for maximizing growth and immune performance (200.381-270.003 mg/kg). In summary, our findings underscore the potential of HK-LP as a valuable dietary supplement for enhancing carp aquaculture, particularly at the appropriate concentration.

The effects of Bacillus subtilis on the immunity, mucosal tissue morphology, immune-related gene transcriptions, and intestinal microbiota in flounder (Paralichthys olivaceus) with two feeding methods: Continuous versus discontinuous feeding

Probiotics as dietary additives can improve weight gain, feed efficiency, and disease resistance in cultured fish. In this research, we evaluated and compared the effects of Bacillus subtilis on immunity, mucosal tissue morphology, immune-related gene transcriptions, and intestinal microbiota in flounder (Paralichthys olivaceus) by a 30-day feeding experiment based on a continuous feeding schedule (E1) and a discontinuous feeding schedule (E2). As a result, the use of B. subtilis exerted the best positive effects on survival rate, enzyme activity, mucosal tissue morphology, immune-related gene transcriptions, and intestinal microbiota in flounders. Alkaline phosphatase (AKP), lysozyme (LZM), and superoxide dismutase (SOD) activities in the liver of E2 were higher than those of E1 (P < 0.05). Furthermore, the villi length in the intestinal tract and the fold length in the stomach of E2 were also higher than in E1 (P < 0.05). The il-1 expression levels in the spleen were significantly increased in E2 (P < 0.05) compared to E1. We performed 16 S rRNA sequencing analysis to find that Bacillus in E1 (1.06%) and E2 (1.01%) had higher relative abundances than in E0 (0.053%) at the end of the experiments, indicating that short-term application of B. subtilis with the continuous or discontinuous feeding method can allow both the adaptation of the ecosystem to the presence of probiotics by the establishment of new species in the gut microbiota and the ability these new probiotic species to perform corresponding functions. No significant differences in the ability of probiotic establishment were observed between E1 and E2. Our findings provided a unique perspective to explore the mechanism of immune enhancement with probiotics and to screen the optimal administration strategy in aquaculture application for probiotic use. Together, these results point to some level of enhancement in immune status by continuous and discontinuous feeding after a short-term feeding period, which could be used as a prophylactic strategy for flounder health management.

Oral immunization with recombinant L. lactis expressing GCRV-II VP4 produces protection against grass carp reovirus infection

The hemorrhagic disease causing by grass carp reovirus (GCRV) infection, is associated with major economic losses and significant impact on aquaculture worldwide. VP4 of GCRV is one of the major outer capsid proteins which can induce an immune response in the host. In this study, pNZ8148-VP4/L. lactis was constructed to express recombinant VP4 protein of GCRV, which was confirmed by the Western-Blot and enzyme-linked immunosorbent assay. Then we performed the oral immunization for rare minnow model and the challenge with GCRV-II. After oral administration, pNZ8148-VP4/L. lactis can continuously reside in the intestinal tract to achieve antigen presentation. The intestinal and spleen samples were collected at different time intervals after immunization, and the expression of immune-related genes was detected by real-time fluorescence quantitative PCR. The results showed that VP4 recombinant L. lactis could induce complete cellular and humoral immune responses in the intestinal mucosal system, and effectively regulate the immunological effect of the spleen. The immunogenicity and the protective efficacy of the oral vaccine was evaluated by determining IgM levels and viral challenge to vaccinated fish, a significant level (P < 0.01) of antigen-specific IgM with GCRV-II neutralizing activity was able to be detected, which provided a effective protection in the challenge experiment. These results indicated that an oral probiotic vaccine with VP4 expression can provide effective protection for grass carp against GCRV-II challenge, suggesting a promising vaccine strategy for fish.

Role of probiotics in managing various human diseases, from oral pathology to cancer and gastrointestinal diseases

The imbalance of microbial composition and diversity in favor of pathogenic microorganisms combined with a loss of beneficial gut microbiota taxa results from factors such as age, diet, antimicrobial administration for different infections, other underlying medical conditions, etc. Probiotics are known for their capacity to improve health by stimulating the indigenous gut microbiota, enhancing host immunity resistance to infection, helping digestion, and carrying out various other functions. Concurrently, the metabolites produced by these microorganisms, termed postbiotics, which include compounds like bacteriocins, lactic acid, and hydrogen peroxide, contribute to inhibiting a wide range of pathogenic bacteria. This review presents an update on using probiotics in managing and treating various human diseases, including complications that may emerge during or after a COVID-19 infection.

Dietary Exogenous α-Amylase Modulates the Nutrient Digestibility, Digestive Enzyme Activity, Growth-Related Gene Expression, and Diet Degradation Rate of Olive Flounder (Paralichthys olivaceus)

In this study, a 12-week feeding experiment was conducted to characterize the effects of exogenous α-amylase on the growth, feed utilization, digestibility, plasma α-amylase activity, feed degradation rate, and fecal particle size of olive flounder (Paralichthys olivaceus). Diet was supplemented with 0 (AA0; control), 100 (AA100), 200 (AA200), or 400 (AA400) mg/kg of α-amylase, respectively. Fish (273.1 ± 2.3 g) were stocked into 12 tanks (25 fish/1,000-L tank) and 3 tanks were randomly selected for each diet group. As a result, α-amylase was found to have no significant effects (p ≥ 0.05) on the growth, feed utilization parameters, and whole-body proximate compositions. α-Amylase-treated fish exhibited only a significant increase in the apparent digestibility coefficient of carbohydrates compared to the controls. In addition, in vitro analyses revealed that α-amylase dose-dependently increased (p < 0.05) the feed degradation rate, while photographs of the intestinal content after 2, 4, and 8 h of feeding demonstrated an improved degradation rate in the α-amylase-treated groups. Plasma α-amylase content was higher in the AA200 and AA400 groups, whereas the control group produced significantly larger-sized fecal particles (90% size class) than these two groups. In the intestine, no changes were observed in the expression levels of the immune-related TNF-α, IL-1β, IL-2, immunoglobulin-M, HSP-70, lysozyme, and amylase alpha-2A. However, growth-related genes IGF-1, IGF-2, TGF-β3, and growth hormone genes were upregulated in muscle tissues. Collectively, exogenous α-amylase has positive roles in the modulation of the digestibility coefficient, blood α-amylase concentration, growth-related gene expression, and diet degradation for improved digestion in olive flounder.

Efficacy of dietary live or heat-killed Bacillus subtilis in goldfish (Carassius auratus) infected with Ichthyophthirius multifiliis

BACKGROUND

The beneficial effects of Bacillus subtilis on growth, immune response, and disease resistance against various diseases in different fish species have been proved. However, there are no data concerning this probiotic effect on skin mucosal immunity in fish infected with Ichthyophthirius multifiliis (Ich). Ich has a high mortality rate in both edible and ornamental fish and consequently is concerned with heavy economic losses.

OBJECTIVES

Thus, we assessed the efficacy of live and heat-killed B. subtilis on skin immunity and histopathology in goldfish (Carassius auratus) infected with Ich.

METHODS

Goldfish (144 fish, 2.38 g average weight) were stocked in nine glass tanks each in three replicates. Fish were fed 10⁹ CFU g^-1 live or heat-killed B. subtilis for 80 days.

RESULTS

Probiotic administration in both viable and non-viable forms could enhance the growth performance in goldfish. Probiotic therapy also reduced the density of the parasite and histopathological level on skin and gill tissues of the treated fish. Real-time polymerase chain reaction analysis showed a higher expression of lysozyme and tumour necrosis factor-α in the treated groups compared to the control group.

CONCLUSIONS

These data demonstrated the beneficial effect of B. subtilis as probiotic and paraprobiotic on growth performance and disease resistance to Ich infestation in goldfish.

Dietary administration of a postbiotic, heat-killed Pediococcus pentosaceus PP4012 enhances growth performance, immune response and modulates intestinal microbiota of white shrimp, Penaeus vannamei

The efficacy of postbiotics on the immune-related gene expression and gut microbiota of white shrimp (Penaeus vannamei) remains unexplored. A commercial heat-killed postbiotic Pediococcus pentosaceus PP4012 was used to evaluate the growth performance, intestinal morphology, immunological status, and microbial community of white shrimp after dietary administration in this study. White shrimp (0.040 ± 0.003 g) were divided into three treatments; a control, inanimate P. pentosaceus (10⁵ CFU g feed^-1) at low concentration (IPL) and inanimate P. pentosaceus (10⁶ CFU g feed^-1) at high concentrations (IPH). The diets of IPL and IPH significantly increased final weight, specific growth rate and production compared to the control group. Shrimp fed with IPL and IPH significantly utilized feed more efficiently than those fed the control diet. The IPH treatment significantly lowered the cumulative mortality rate compared to the control and IPL diet following Vibrio parahaemolyticus infection. No significant difference was observed for Vibrio-like and lactic acid bacteria in intestine of shrimp fed with the control diet and the experimental diets. Adding inanimate P. pentosaceus significantly improved immune responses such as lysozyme and phagocytic activity compared to the control group. However, the total hemocyte count, phenoloxidase activity, respiratory burst, and superoxide dismutase were not significantly different among treatments. The immune-related genes alf, pen3a, and pen4 expression were significantly higher in shrimp fed IPL diet compared with control and IPH. Taxonomic identification of bacterial genera in all dietary groups belonged to two predominant phyla, Proteobacteria and Bacteroidota. An abundance of Photobacterium, Motilimonas, Litorilituus, and Firmicutes bacterium ZOR0006 were identified in the intestine of shrimp fed postbiotic diets. Unique microbes such as Cohaesibacter was discovered in the shrimp fed IPL while Candidatus Campbellbacteria, uncultured Verrucomicrobium DEV114 and Paenalcaligenes were discovered in the intestines of shrimp fed IPH diet. Collectively, these data suggest that including heat-killed P. pentosaceus, particularly IPH, can enhance growth performance, promote microbial diversity, elevate immune responses, and increase shrimp's resistance to V. parahaemolyticus.

Commensal Bacillus siamensis LF4 ameliorates β-conglycinin induced inflammation in intestinal epithelial cells of Lateolabrax maculatus

β-conglycinin and glycinin, two major heat-stable anti-nutritional factors in soybean meal (SM), have been suggested as the key inducers of intestinal inflammation in aquatic animals. In the present study, a spotted seabass intestinal epithelial cells (IECs) were used to compare the inflammation-inducing effects of β-conglycinin and glycinin. The results showed that IECs co-cultured with 1.0 mg/mL β-conglycinin for 12 h or 1.5 mg/mL glycinin for 24 h significantly decreased the cell viability (P < 0.05), and overstimulated inflammation and apoptosis response by significantly down-regulating anti-inflammatory genes (IL-2, IL-4, IL-10 and TGF-β1) expressions and significantly up-regulated pro-inflammatory genes (IL-1β, IL-8 and TNF-α) and apoptosis genes (caspase 3, caspase 8 and caspase 9) expressions (P < 0.05). Subsequently, a β-conglycinin based inflammation IECs model was established and used for demonstrating whether commensal probiotic B. siamensis LF4 can ameliorate the adverse effects of β-conglycinin. The results showed β-conglycinin-induced cell viability damage was completely repaired by treated with 10⁹ cells/mL heat-killed B. siamensis LF4 for ≥12 h. At the same time, IECs co-cultured with 10⁹ cells/mL heat-killed B. siamensis LF4 for 24 h significantly ameliorated β-conglycinin-induced inflammation and apoptosis by up-regulating anti-inflammatory genes (IL-2, IL-4, IL-10 and TGF-β1) expressions and down-regulated pro-inflammatory genes (IL-1β, IL-8 and TNF-α) and apoptosis genes (caspase 3, caspase 8 and caspase 9) expressions (P < 0.05). In summary, both β-conglycinin and glycinin can lead to inflammation and apoptosis in spotted seabass IECs, and β-conglycinin is more effective; commensal B. siamensis LF4 can efficiently ameliorate β-conglycinin induced inflammation and apoptosis in IECs.

Evaluation of the Combined Administration of Chlorella fusca and Vibrio proteolyticus in Diets for Chelon labrosus: Effects on Growth, Metabolism, and Digestive Functionality

This study aimed to evaluate the combined effect of dietary Chlorella fusca and ethanol-inactivated Vibrio proteolyticus DCF12.2 (C + V diet) in Chelon labrosus juveniles, highlighting their nutritional, physiological, and morphological effects. The results showed that the combined dietary inclusion of C. fusca and V. proteolyticus significantly enhanced growth performance and feed utilization compared to the control group. The C + V diet increased the fish lipid quality index (FLQ), n-3 polyunsaturated fatty acids, and n-3/n-6 ratio, which might be beneficial in terms of human nutrition. The C + V diet considerably increased carbohydrate metabolic activity by statistically boosting plasma glucose. The dietary inclusion of C. fusca in conjunction with V. proteolyticus increased metabolic enzyme activity as well as intestinal absorption capacity compared to that found in the control group. In conclusion, the experimental diet was suitable for feeding C. labrosus, increasing their growth and the nutritional characteristics of the muscle and intestine, without causing tissue damage.

Protective immunity against spring viremia of carp virus by mannose modified chitosan loaded DNA vaccine

Spring viremia of carp virus (SVCV) usually be considered as one of the serious in viral diseases of aquaculture, and DNA vaccine with novel delivery mechanism or adjuvant has proven to be a promising and effective strategy to control aquatic animal diseases. In this study, the mannose-modified chitosan, a carrier system for vaccine delivery, were used to developed a chitosan-encapsulated DNA vaccine (CS-M-G) against SVCV, then investigated immune response induced by the vaccine. Our results showed that CS-M-G was confirmed the spherical or elliptical with even distribution and ranging from approximately 50 to 150 nm in size, the expression of the antigen gene could still be detected after 21 d post vaccination. The CS-M-G induces the highest antibody levels in the 20 μg dose group which is about 3 times than naked plasmid group at 21 d post vaccination, and still hold a higher level than control group at 28 d post vaccination. On the side, strongest protection with relative percent survival of 62.1% in the 20 μg CS-M-G group, which could produce significantly higher enzyme activities and up-regulated expression of immune-associated genes than control group. Thus, our results indicate that DNA vaccine loaded with mannose-modified chitosan induces strong immune response and provided an effective protection against SVCV infection, may be helpful and extended for developing more aquatic animal vaccines in the future.

Bacillus-derived probiotics: metabolites and mechanisms involved in bacteria-host interactions

Bacillus probiotics have a sporulation capacity that makes them more suitable for processing and storage and for surviving passage through the gastrointestinal tract. The probiotic functions and regulatory mechanisms of different Bacillus have been exploited in many reports, but little is known about how various Bacillus probiotics perform different functions. This knowledge gap results in a lack of specificity in the selection and application of Bacillus. The probiotic properties are strain-specific and cell-type-specific, and are related to the germination potential and to the diversity of metabolites produced following intestinal germination, as this causes the variation in probiotic function and mechanisms. In this review, we discuss the Bacillus metabolites produced during germination and sporulation in the GI tract, as well as possible processes affecting intestinal homeostasis. We conclude that the oxygen-capturing capability and the production of antimicrobials, exoenzymes, competence and sporulation factors (CSF), exopolysaccharides, lactic acid, and cell components are specifically associated with the functional mechanisms of probiotic Bacillus. The aim of this review is to guide the screening of potential Bacillus strains for probiotics and their application in nutrition research. The information provided will also promote further research on Bacillus-derived functional metabolites in human nutrition.

Effects of Decreasing Fishmeal as Main Source of Protein on Growth, Digestive Physiology, and Gut Microbiota of Olive Flounder (Paralichthys olivaceus)

Simple Summary

The demand for fishmeal is increasing due to aquaculture development, but the supply is unstable. This indicates the need to reduce the fishmeal content in the feed and develop an optimal fish-feed formulation through substitutes. However, most studies on reducing fishmeal content in feed were conducted at the laboratory level. In this study, the application of a low-fishmeal diet as feed to olive flounder was evaluated in terms of growth-related factors, digestive physiology, and microbiota raised for five months in a fish farm using four feed formulations- FM70 [control (CON), 70% fishmeal], FM45 (45% fishmeal), FM35A (35% fishmeal), and FM35B (35% fishmeal + insect meal). There was no difference in growth-related factors, digestive physiology, and gut microbiota diversity compared with the CON-fed fish. Therefore, reducing the fishmeal content of the feed by up to 35% does not adversely affect growth and physiological characteristics under farm conditions.

Abstract

In olive flounder (Paralichthys olivaceus), growth performance, expression of growth-related factors, digestive physiology, and gut microbiota were assessed under farm conditions in the fish fed diets with low levels of fishmeal. Four experimental diets were prepared, FM70 [control (CON), 70% fishmeal], FM45 (45% fishmeal), FM35A (35% fishmeal), and FM35B (35% fishmeal + insect meal), and fed to the fish for five months. The CON-fed fish had the highest plasma GH, but IGF-1 and hepatic IGF-1 mRNA expression of the olive flounder fed diets with low-fishmeal levels did not significantly differ among diets. The intestinal villus length, muscular thickness, and the number of goblet cells were statistically similar, and ocular examination of hepatopancreas showed no discernable difference in all experimental diets. The chymotrypsin content of FM35B-fed fish is significantly lower, but trypsin and lipase contents are similar. The diversity of gut microbiota did not differ among groups, although the FM35B group had a higher composition of Firmicutes. Thus, a diet with reduced fishmeal content and several alternative protein sources can be used as feed ingredients in feed formulation for olive flounder reared under typical aquaculture farm conditions.

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

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

Evaluation of Dietary Probiotic Bacteria and Processed Yeast (GroPro-Aqua) as the Alternative of Antibiotics in Juvenile Olive Flounder Paralichthys olivaceus

We investigated the three probiotic bacteria and a processed yeast (GroPro-Aqua) as the replacers of antibiotics in juvenile olive flounder. A total of seven diets were used, that is, one basal or control (CON) diet; and six other diets, of which, three diets were prepared by supplementing probiotic bacteria such as Bacillus subtilis WB60 (BSWB60) at 1 × 10⁸ CFU/g diet, Bacillus subtilis SJ10 (BSSJ10) at 1 × 10⁸ CFU/g diet, and Enterococcus faecium SH30 (EFSH30) at 1 × 10⁷ CFU/g diet; one diet with processed yeast (GRO) at 0.35% diet; and two other diets were supplemented with oxytetracycline (OTC) and amoxicillin (AMO) at 4 g/kg of each. Triplicate groups of fish (average 12.1 g) were fed one of the diets for eight weeks. At the end of the feeding trial, the fish that were fed the probiotic bacteria-supplemented diets had a significantly higher final weight, weight gain, and specific growth rate compared to the CON, OTC, and AMO diets. Fish that were fed the GRO diet had significantly higher feed efficiency and protein efficiency ratios than those of the fish that were fed the CON diet. Serum glutamic pyruvic transaminase, glutamic oxaloacetic transaminase, glucose, and total protein were not affected by the diets. Lysozyme activity in fish that were fed the BSSJ10, BSWB60, and EFSH30 diets were significantly higher compared to the CON and OTC diets, whereas myeloperoxidase activity of fish fed the BSWB60 and EFSH30 diets were significantly higher than those of fish fed the CON and AMO diets. Flounder growth hormone gene expressions of fish that were fed BSWB60 and GRO diets were significantly higher compared to the CON, OTC, and AMO diets. The interleukin-1β gene expression of fish that were fed the BSSJ10, BSWB60, EFSH30, OTC, and GRO diets was significantly higher than those of fish fed the CON diet. The interleukin-10 gene expression of fish that were fed the BSSJ10, EFSH30, and GRO diets was significantly higher than those of fish fed the CON and AMO diets. Posterior intestinal histology of fish showed significantly higher villi length in fish that were fed the BSSJ10, BSWB60, EFSH30, and GRO diets compared to the CON diet. After 15 days of challenge test with pathogenic bacteria Edwardsiella tarda, the cumulative survival rate of fish that were fed the BSSJ10, BSWB60, EFSH30, and GRO diets were significantly higher than those of fish that were fed the CON diet. Overall, the results indicate that dietary supplementation of B. subtilis (10⁸ CFU/g diet), E. faecium (10⁷ CFU/g diet), and processed yeast (GroPro-Aqua at 0.35% diet) could replace the antibiotics in terms of improving growth, immunity, gut health, and disease resistance in juvenile olive flounder.

Screening of New Potential Probiotics Strains against Photobacterium damselae Subsp. piscicida for Marine Aquaculture

On intensive fish farms, 10% of the population dies exclusively from pathogens, and Photobacterium damselae subsp. Piscicida (Ph. damselae subsp. Piscicida), the bacteria causing pasteurellosis in marine aquaculture, is one of the major pathogens involved. The objective of this study was to obtain new probiotic strains against pasteurellosis in order to limit the use of chemotherapy, avoiding the environmental repercussions generated by the abusive use of these products. In this study, 122 strains were isolated from the gills and intestines of different marine fish species and were later evaluated in vitro to demonstrate the production of antagonistic effects, the production of antibacterial substances, adhesion and growth to mucus, resistance to bile and resistance to pH gradients, as well as its harmlessness and the dynamic of expression of immune-related genes by real-time PCR after administration of the potential probiotic in the fish diet. Only 1/122 strains showed excellent results to be considered as a potential probiotic strain and continue its characterization against Ph. damselae subsp. piscicida to determine its protective effect and elucidating in future studies its use as a possible probiotic strain for marine aquaculture.

Oral Probiotic Vaccine Expressing Koi Herpesvirus (KHV) ORF81 Protein Delivered by Chitosan-Alginate Capsules Is a Promising Strategy for Mass Oral Vaccination of Carps against KHV Infection

Koi herpesvirus (KHV) is highly contagious and lethal to cyprinid fish, causing significant economic losses to the carp aquaculture industry, particularly to koi carp breeders. Vaccines delivered through intramuscular needle injection or gene gun are not suitable for mass vaccination of carp. So, the development of cost-effective oral vaccines that are easily applicable at a farm level is highly desirable. In this study, we utilized chitosan-alginate capsules as an oral delivery system for a live probiotic (Lactobacillus rhamnosus) vaccine, pYG-KHV-ORF81/LR CIQ249, expressing KHV ORF81 protein. The tolerance of the encapsulated recombinant Lactobacillus to various digestive environments and the ability of the probiotic strain to colonize the intestine of carp was tested. The immunogenicity and the protective efficacy of the encapsulated probiotic vaccine was evaluated by determining IgM levels, lymphocyte proliferation, expression of immune-related genes, and viral challenge to vaccinated fish. It was clear that the chitosan-alginate capsules protected the probiotic vaccine effectively against extreme digestive environments, and a significant level (P < 0.01) of antigen-specific IgM with KHV-neutralizing activity was detected, which provided a protection rate of ca. 85% for koi carp against KHV challenge. The strategy of using chitosan-alginate capsules to deliver probiotic vaccines is easily applicable for mass oral vaccination of fish.IMPORTANCE An oral probiotic vaccine, pYG-KHV-ORF81/LR CIQ249, encapsulated by chitosan-alginate capsules as an oral delivery system was developed for koi carp against koi herpesvirus (KHV) infection. This encapsulated probiotic vaccine can be protected from various digestive environments and maintain effectively high viability, showing a good tolerance to digestive environments. This encapsulated probiotic vaccine has a good immunogenicity in koi carp via oral vaccination, and a significant level of antigen-specific IgM was effectively induced after oral vaccination, displaying effective KHV-neutralizing activity. This encapsulated probiotic vaccine can provide effective protection for koi carp against KHV challenge, which is handling-stress free for the fish, cost effective, and suitable for the mass oral vaccination of koi carp at a farm level, suggesting a promising vaccine strategy for fish.

Evaluation of Dietary Soluble Extract Hydrolysates with or without Supplementation of Inosine Monophosphate Based on Growth, Hematology, Non-Specific Immune Responses and Disease Resistance in Juvenile Nile Tilapia Oreochromis niloticus

Simple Summary

This study was conducted to elucidate the effects of dietary soluble extract hydrolysates obtained from fishery by-products, such as shrimp soluble extract (SSE), tilapia soluble extract (TSE) and squid soluble extract (SQSE). Furthermore, we used a nucleotide, inosine monophosphate (IMP), as an additive in different concentrations along with shrimp soluble extract to understand their effects on growth, immunity and disease resistance in juvenile Nile tilapia. Our results demonstrated that dietary SSE could improve growth performance, non-specific immune responses and disease resistance against pathogenic bacteria Aeromonas hydrophila in juvenile Nile tilapia. Moreover, IMP did not add further benefits to the SSE diet. Further research is needed to better understand the effects of fishery by-products and IMP on fish diets.

Abstract

We performed an 8-week feeding trial to evaluate dietary soluble extract hydrolysates from fishery by-products, such as shrimp soluble extract (SSE) with or without inosine monophosphate (IMP), tilapia soluble extract (TSE) and squid soluble extract (SQSE), in juvenile Nile tilapia. A diet without feed additives was used as the control diet (CON); and five other experimental diets were formulated with 2% soluble extracts consisting of 100% SSE, 98% SSE + 2% IMP (SSEP₂), 96% SSE + 4% IMP (SSEP₄), 100% SQSE and 100% TSE. The diets were fed to 4.9 ± 0.07 g (mean ± SD) juvenile Nile tilapia in triplicate groups. The weight gain and specific growth rates of fish fed the SSE, SSEP₂ and SSEP₄ diets were significantly higher than those of fish fed the CON and SQSE diets. The superoxide dismutase activity levels of fish fed the SSE and SSEP₄ diets were significantly higher than those of fish fed the CON, SSEP₂, SQSE and TSE diets. Myeloperoxidase activity levels of fish fed the SSE and SSEP₄ diets were significantly higher than those of fish fed the CON, SSEP₂ and SQSE diets. Lysozyme activity levels of fish fed the SSEP₄ and SQSE diets were significantly higher than those of fish fed the SSE and SSEP₂ diets. Feed efficiency, protein efficiency ratio, survival rate, whole body proximate composition and hematological parameters were not significantly different among the groups. After ten days of challenge = against Aeromonas hydrophila, the cumulative survival rate of fish fed the SSE diet was significantly higher than those of fish fed the CON, SQSE and TSE diets. In conclusion, dietary shrimp soluble extract could improve the growth performance, non-specific immune responses and disease resistance in juvenile Nile tilapia, and inosine monophosphate did not add further benefits to this ingredient.

A Tentative Study of the Effects of Heat-Inactivation of the Probiotic Strain Shewanella putrefaciens Ppd11 on Senegalese Sole (Solea senegalensis) Intestinal Microbiota and Immune Response

Concerns about safety, applicability and functionality associated with live probiotic cells have led to consideration of the use of non-viable microorganisms, known as paraprobiotics. The present study evaluated the effects of dietary administration of heat-inactivated cells of the probiotic strain Shewanella putrefaciens Ppd11 on the intestinal microbiota and immune gene transcription in Solea senegalensis. Results obtained were evaluated and compared to those described after feeding with viable Pdp11 cells. S. senegalensis specimens were fed with basal (control) diet or supplemented with live or heat inactivated (60 °C, 1 h) probiotics diets for 45 days. Growth improvement was observed in the group receiving live probiotics compared to the control group, but not after feeding with a probiotic heat-inactivated diet. Regarding immune gene transcription, no changes were observed for tnfα, il-6, lys-c1, c7, hsp70, and hsp90aa in the intestinal samples based on the diet. On the contrary, hsp90ab, gp96, cd4, cd8, il-1β, and c3 transcription were modulated after probiotic supplementation, though no differences between viable and heat-inactivated probiotic supplemented diets were observed. Modulation of intestinal microbiota showed remarkable differences based on the viability of the probiotics. Thus, higher diversity in fish fed with live probiotic cells, jointly with increased Mycoplasmataceae and Spirochaetaceae to the detriment of Brevinemataceae, was detected. However, microbiota of fish receiving heat-inactivated probiotic cells showed decreased Mycoplasmataceae and increased Brevinemataceae and Vibrio genus abundance. In short, the results obtained indicate that the viable state of Pdp11 probiotic cells affects growth performance and modulation of S. senegalensis intestinal microbiota. On the contrary, minor changes were detected in the intestinal immune response, being similar for fish receiving both, viable and inactivated probiotic cell supplemented diets, when compared to the control diet.

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.

Antiparasitic and Antibacterial Functionality of Essential Oils: An Alternative Approach for Sustainable Aquaculture

Using synthetic antibiotics/chemicals for infectious bacterial pathogens and parasitic disease control causes beneficial microbial killing, produces multi-drug resistant pathogens, and residual antibiotic impacts in humans are the major threats to aquaculture sustainability. Applications of herbal products to combat microbial and parasitic diseases are considered as alternative approaches for sustainable aquaculture. Essential oils (EOs) are the secondary metabolites of medicinal plants that possess bioactive compounds like terpens, terpenoids, phenylpropenes, and isothiocyanates with synergistic relationship among these compounds. The hydrophobic compounds of EOs can penetrate the bacterial and parasitic cells and cause cell deformities and organelles dysfunctions. Dietary supplementation of EOs also modulate growth, immunity, and infectious disease resistance in aquatic organisms. Published research reports also demonstrated EOs effectiveness against Ichthyophthirius multifiliis, Gyrodactylus sp., Euclinostomum heterostomum, and other parasites both in vivo and in vitro. Moreover, different infectious fish pathogenic bacteria like Aeromonas salmonicida, Vibrio harveyi, and Streptococcus agalactiae destruction was confirmed by plant originated EOs. However, no research was conducted to confirm the mechanism of action or pathway identification of EOs to combat aquatic parasites and disease-causing microbes. This review aims to explore the effectiveness of EOs against fish parasites and pathogenic bacteria as an environment-friendly phytotherapeutic in the aquaculture industry. Moreover, research gaps and future approaches to use EOs for sustainable aquaculture practice are also postulated.

Effects of dietary white mulberry leaves on hemato-biochemical alterations, immunosuppression and oxidative stress induced by Aeromonas hydrophila in Oreochromis niloticus

The present work was designed to assess the potential hemato-biochemical protective action, immunemodulatory and antioxidant conclusions of varied concentration of white mulberry Morus alba leaves (MAL) extract supplementation on Nile tilapia (Oreochromis .niloticus). A total two hundred and forty of O. niloticus were haphazardly sorted into four groups. The control (CT) group was fed on basal diet. A group MAL₁, MAL₃ and MAL₅ was fed on 1, 3 and 5 g/kg MAL respectively for thirty days. On day thirty one, half of replicates in each group were challenged by 0.5 ml × 10⁸Aeromonas hydrophila where, the residual replicates were kept without challenge. A. hydrophila challenged tilapias revealed anemia that alleviated by supplementation with 5 g/kg MAL also, recovers the shift of leucogram prompted by the challenge. Elevation of alkaline phosphatase, aminotransferases, lactate dehydrogenase and malondialdehyde (ALP, ALT, AST, LDH and MDA) in CT, MAL₁ and MAL₃ in the challenged replicates respectively where within normal at MAL₅. Supplementation with MAL₅ showed more potent antioxidant and immune reaction than MAL₁ and MAL₃. There were a rapid increase of immunoglobulin M, lysozymes, nitric oxide, catalase and superoxide dismutase and their allied genes expression (IgM, CAT and SOD) in MAL groups with contrast in CT challenged groups. Where in challenged groups, there was suppression in genes expression of interleukins (8 and 1 beta) and interferon ɤ (IL8. IL-1β and INFɤ). Tilapias challenged by A. hydrophila unveiled plentiful surge in the percentage of mortality in CT challenged fish (80%), followed by the groups supplemented with MAL₁ and MAL₃ were (73.33%) where MAL₅ was 20%. The mortalities have been halted from the 6^th, 13^th, 14^th and 15^th days in, MAL₅, MAL₃, MAL₁, and CT correspondingly. These previous results could be fulfilled that using of MAL 5 g/kg protect tilapias from hemato-biochemical alterations and enhance its immune feedback, antioxidant defense and resistance against A. hydrophila.

Immune-stimulating Effect of Lactobacillus plantarum Ln1 Isolated from the Traditional Korean Fermented Food, Kimchi

This study aimed to determine the immune-stimulating effects of heat-killed Lactobacillus plantarum Ln1 (HK-Ln1) through the production of nitric oxide (NO) and pro-inflammatory cytokine achieved by inducing NF-κB and mitogen-activated protein kinase (MAPK)-signaling pathways in macrophages. HK-Ln1 showed higher NO and cytokine production compared t°Control (nonstimulated lipopolysaccharide); in addition, the expression of inducible nitric oxide synthase (iNOS) was induced through HK-Ln1treatment. The phosphorylation of IκB-α and p65 increased following treatment by HK-Ln1, which implicates IκB-α degradation and the translocation of p65 to nucleus. In addition, the phosphorylation of MAPKs, ERK 1/2, JNK, and p38 was induced following HK-Ln1 treatment.

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.

Growth performance and hemato-immunological responses of Nile tilapia (Oreochromis niloticus) exposed to deltamethrin and fed immunobiotics

The use of feed additives in aquatic animals improves health conditions and well-being under pesticide toxicity. Thus, this study was aimed at evaluating the effect of an immunobiotic mixture (IM) on the growth performance, hemato-biochemistry, and immunity of Nile tilapia exposed to subacute deltamethrin (DMT). Fish were distributed into four groups: groups 1 and 2 were fed a control diet, while groups 3 and 4 were fed IM. Groups 2 and 4 were exposed to DMT (15 μg/L) in rearing water. The results revealed that DMT-exposed fish exhibited significantly lower final body weights, weight gain, specific growth rate, and survival rate (P < 0.05), while IM feeding resulted in improved growth performance and survival rate in fish with or without DMT toxicity. After 15 and 30 days, DMT-treated fish showed a significant increase in blood urea and bilirubin as well as hepatic enzymes (alkaline phosphatase, aspartate aminotransferase, and alanine aminotransferase) (P < 0.05), while supplementation of the IM mixture significantly lowered these levels in Nile tilapia. Blood total protein, globulin, albumin, white blood cells, red blood cells, hemoglobin, phagocytic index, and phagocytic and lysozyme activities were significantly decreased in tilapia subjected to DMT (P < 0.05), while supplementation of the IM mixture significantly increased these levels. Fish fed IM without DMT exposure showed the lowest cortisol and glucose levels, while fish exposed to DMT without IM showed the highest levels (P < 0.05) after 15 and 30 days. To conclude, IM supplementation exhibited defensive effects against DMT toxicity in Nile tilapia by improving growth performance, hematology, blood biochemistry, and immunity.

Lactobacillus plantarum L-137 and/or β-glucan impacted the histopathological, antioxidant, immune-related genes and resistance of Nile tilapia (Oreochromis niloticus) against Aeromonas hydrophila

A trial was operated to assess the potential of using Lactobacillus plantarum L-137 (L-137) and/or β-glucan (BG) in improving the resistance of Nile tilapia against Aeromonas hydrophila. Control diet and 3 diets supplemented with L-137, BG or L-137 + BG were prepared. Final body weight, specific growth rate, superoxide dismutase, and catalase showed considerably (P < .05) increased values in L-137 or L-137/BG groups, while glutathione peroxidase increased significantly (P < .05) only in L-137/BG group. Fish fed L-137 and/or BG diets showed that feed conversion ratio and malonaldehyde levels were significantly decreased (P < .05). Also, both L-137 and BG helped Nile tilapia to have high phagocytosis activity and relative expression of tumor necrosis factor-alpha (TNF-α) and interleukin 1 beta (IL-1β) and interferon-gamma (INF-γ) genes. After A. hydrophila challenge, the intestinal villi epithelium of the L-137/BG group was intact and denser than the other groups. The hepatopancreas and spleen of the control group displayed severe necrosis in hepatocytes and congestion of blood sinusoids in addition to diffuse vacuolation. Regarding the L-137, BG and L-137/BG groups, there was a moderate and normal degree of vacuolation with focal necrosis and mild to moderate degree of congestion of blood sinusoids. Red blood cells, hemoglobin, and albumin showed meaningfully (P < .05) increased values in L-137 or L-137/BG groups. TNF-α, IL-1β, and INF-γ expressions were upregulated by L-137 and/or BG. The obtained results revealed the ability of L-137 and/or BG to protect Nile tilapia from the effects of A. hydrophila infection by the motivation of the immune, antioxidative, and antiinflammation responses.

The influence of dietary β-glucan on immune, transcriptomic, inflammatory and histopathology disorders caused by deltamethrin toxicity in Nile tilapia (Oreochromis niloticus)

The protective role of β-glucan (BG) on liver function, histopathology, immune and antioxidant related gene expressions in Nile tilapia exposed to subacute deltamethrin (DLM) was investigated for 30 days. Fish (28.18 ± 1.34 g) of the 1st and 2nd groups fed the control diet, while the 3rd and 4th groups fed BG at 0.5 g/kg and the 2nd and 4th groups were exposed to DLM (15 μg/L) in rearing water. DLM-treated fish displayed a considerable increase in blood biochemical parameters (creatinine, urea and bilirubin) as well as hepatic enzymes (ALP, AST and ALT) (P < 0.05). Blood total protein, globulin, albumin, WBCs, RBCs, Hb, phagocytic index, phagocytic and lysozyme activities were significantly decreased in fish subjected to DLM (P < 0.05). Fish fed BG showed significantly the lowest cortisol and glucose levels, while fish exposed to DLM without feeding BG showed the highest cortisol and glucose levels (P < 0.05) after 15 and 30 days. Additionally, DLM toxicity caused downregulation in antioxidant (CAT and GPx) and immune (IL-1β and IL-8) related gene expressions, while and IFN-γ, HSP70 and CASP3 were upregulated. The histopathological examination of Nile tilapia exposed to DLM revealed damage in gills, intestine, spleen and liver which confirmed the toxic effects. Conversely, BG presented protective effects and restored the above-mentioned parameters when fish exposed to DLM and fed BG. Thus, BG supplementation exhibited defensive effects against DLM toxicity in Nile tilapia through improving blood biochemical responses, immune, and antioxidant related gene expressions as well as histopathological effects.

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.

Ameliorative effects of Lactobacillus plantarum L-137 on Nile tilapia (Oreochromis niloticus) exposed to deltamethrin toxicity in rearing water

Deltamethrin (DLM) is a synthetic pyrethroid used for agricultural purposes to control insects and has been found to pollute the aquatic environment and leads to serious health problems. Lactobacillus plantaruml-137 (L-137) has gained more popularity as functional supplement for its immunomodulatory effects and antioxidant potential. This study was designed to examine the potential of l-137 on liver function, histopathology, immune and antioxidant related gene expressions in Nile tilapia exposed to subacute DLM for 30 days. Fish (mean weight of 28.18 ± 1.34 g) was distributed into four groups (triplicates): the first and second groups fed the control diet, while the third and fourth groups fed l-137 at 50 mg/kg and the second and fourth groups were exposed to DLM (15 μg/L) in rearing water (control, DLM, l-137 and DLM + L-137, respectively). DLM-treated fish groups showed a significant increase in blood biochemical parameters (creatinine, urea and bilirubin) as well as hepatic enzymes (ALP, AST and ALT) (P < 0.05). Blood total protein, globulin, albumin, WBCs, RBCs, Hb, phagocytic index, phagocytic and lysozyme activities were significantly decreased in fish exposed to DLM (P < 0.05). Additionally, DLM toxicity downregulated the transcription of immune genes (IL-1β and IL-8), while upregulated the stress related genes (HSP70 and CASP3). The histopathological images of Nile tilapia exposed to DLM revealed damage in gills, intestine, spleen and liver which confirmed the toxic effects. Conversely, l-137 presented protective effects and restored the aforementioned parameters when fish exposed to DLM and fed l-137. Further, l-137 restored the antioxidative capacity (CAT and GPx). Thus, l-137 supplementation exhibited defensive effects against DLM toxicity in Nile tilapia through improving blood biochemical responses, immune, and antioxidant related gene expressions as well as histopathological effects.

Effects of probiotic supplementation of a plant-based protein diet on intestinal microbial diversity, digestive enzyme activity, intestinal structure, and immunity in olive flounder (Paralichthys olivaceus)

The aim of this study was to investigate the effects of intestinal microbial manipulation by dietary probiotic supplementation on digestive enzyme activity, immune-related gene transcription, intestinal structure alteration, and viability against pathogenic challenge in olive flounder. Similar-sized flounders (14.92 ± 0.21 g) were divided into three groups and supplemented with a control (without probiotic) or 1 × 10⁸ CFU/g diet of each of Bacillus sp. SJ-10 (ProB) and Lactobacillus plantarum (ProL) for eight weeks. At the end of the feeding trial, the estimated intestinal microbial richness (Chao1) and diversity (Shannon) demonstrated a significant (P < 0.05) abundance in the ProB group (484.80 ± 88.75, 5.08 ± 0.17) compared to the ProL (285.32 ± 17.78, 4.54 ± 0.09) and control groups (263.23 ± 20.20, 4.30 ± 0.20). A similar alteration phenomenon was also found at the phylum level, with a higher abundance of Proteobacteria, Actinobacteria, and Acidobacteria. Trypsin and lipase activities were elevated in both the ProB and ProL groups compared to the control, but amylase was only higher in the ProB group. The expression levels of pro-inflammatory cytokines, such as tumor necrosis factor-α, interleukin (IL)-1β, and IL-6 were significantly higher in the ProB group than in the other two groups. There was a significant increase in transcription of IL-10 in both the ProB and ProL groups compared to the control. The length of villi and microvilli of probiotic-fed olive flounder was increased but was not significantly different from the control group. In an in vivo challenge experiment with Streptococcus iniae (1 × 10⁸ CFU/mL), the survival rates of the ProB and ProL groups were 29.17% and 12.50%, respectively, when control mortality reached 100%. Therefore, intestinal microbiota manipulation by probiotic supplementation increased the richness of the bacterial population, digestive enzyme activity, intestinal immune gene transcription, and infectious disease protection in olive flounder.