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

Screening and effects of intestinal probiotics on growth performance, gut health, immunity, and disease resistance of Nile tilapia (Oreochromis niloticus) against Streptococcus agalactiae

In the present study, 59 autochthonous bacteria were isolated from the intestine of tilapia. Following enzyme producing activity, antagonistic ability, hemolytic activity, drug sensitivity assessments, and in vivo safety evaluation, 7 potential probiotic strains were screened out: Bacillus tequilensis BT0825-2 (BT), Bacillus aryabhattai BA0829-3 (BA1), Bacillus megaterium BM0505-6 (BM), Bacillus velezensis BV0505-11 (BV), Bacillus licheniformis BL0505-18 (BL), B. aryabhattai BA0505-19 (BA2), and Lactococcus lactis LL0306-15 (LL). Subsequently, tilapia were fed basal diets (CT) and basal diets supplemented with 108 CFU/g of BT, BA1, BM, BV, BL, BA2 and LL, respectively. After 56 days of continuous feeding, the growth parameters (weight gain, final weight, and specific growth rate) showed significant improvement (p < 0.05) in both BM and BA2 groups. The total cholesterol and triglycerides of serum were significantly decreased in BV and LL groups (p < 0.05). The superoxide dismutase, glutathione reductase, and lysozyme of BV, BA2 and LL groups were increased, and the malondialdehyde of BV group was significantly decreased. The villous height and amylase of midgut were increased in BV, BA2 and LL groups. In addition, the expression levels of ZO-1 and occludin genes in the midgut of tilapia were enhanced in BM, BV, BA2 and LL groups. The supplementation of probiotics reduced the abundance of Cyanobacteria and increased the abundance of Actinobacteria at the phylum level. At the genus level, the addition of probiotics increased the abundance of Romboutsia. Furthermore, improvement in the expression of immune-related genes were observed, including interleukin 1β, interleukin 10, tumor necrosis factor alpha, and transforming growth factor beta (p < 0.05). After challenging with S. agalactiae, the survival rates of BV, BA2 and LL groups were significantly higher than CT group (p < 0.05). Above results indicated that BM, BA2, BV and LL improved growth performance, gut health or immunity of tilapia, which can be applied in tilapia aquaculture.

Evaluation of different probiotics on growth, body composition, antioxidant capacity, and histoarchitecture of Mugil capito

We investigated the dietary effects of the single application of Saccharomyces cerevisiae, Lactobacillus bulgaricus, and their combination on growth, proximate composition of whole fish body, antioxidant defense, and histoarchitecture of hapa-reared Mugil capito. Healthy fish (Fish weighed = 10.30 ± 0.10 g at first) were randomly allocated into 4 equal groups, each with three replicates. These groups were designed as follows: (1) a group fed a basal diet without probiotics (control), (2) a group fed a diet containing S. cerevisiae (4 g/kg diet), (3) a group fed a diet containing L. bulgaricus (2 g/kg diet), and (4) the last group fed a diet containing a combination of both, all for a duration of 60 days. Probiotic-treated groups showed significantly better growth and nutrition utilization than the control group. Significant differences were observed in the crude fat and crude protein contents among the groups, with the combination group exhibiting the highest levels. However, there were no significant variations in ash content across all groups. The highest hepatic antioxidant capacity (superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX) enzyme activities) was observed in the combination group. Thiobarbituric acid reactive substance (TBARS) concentrations were decreased significantly in all probiotic groups, suggesting improved oxidative stress resilience in these groups. The histomorphological analysis of the hepatopancreatic tissues revealed well-arranged parenchyma, increased glycogen storage, and melanomacrophage centers in probiotic-treated groups, particularly the combined probiotics group. Furthermore, the probiotic supplementation improved the histoarchitecture of the intestinal villi compared to the control group. To put it briefly, combined dietary administration of these probiotics improved growth, body composition, antioxidant defenses, and hepatic and intestinal health in hapa-reared M. capito, highlighting their promising role in promoting welfare and productivity.

Effects of Dietary Medlar (Mespilus germanica L.) Extract on Growth Performance, Innate Immune Characteristics, Antioxidant Status, and Responses to Crowding Stress in Rainbow Trout (Oncorhynchus mykiss)

High stocking density is a stress factor that potentially affects physiological and immune responses. In this study, the effects of medlar (Mespilus germanica) extract (ME) supplementation on growth performance, antioxidant, immune status, and stress responses in rainbow trout (Oncorhynchus mykiss) were studied. Six hundred fish (40.19 ± 1.09 g; average fish weight ± standard error) were distributed randomly into five experimental groups (assayed in triplicates). The experimental diets were formulated as follows: 0 (T1, control), 0.5% (T2), 1% (T3), 1.5% (T4), and 2% (T4). After 60 days feeding trial, the fish were confined, and the density increased (60 kg/m3) for further 14 days. Results showed significant increases in final weight (FW), weight gain (WG), specific growth rate, and feed intake in the T4 compared to the control (P < 0.05). The feed conversion ratio (FCR) in T4 significantly decreased compared to the control (P < 0.05). Also, the treated groups showed significant improvements in catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), lysozyme (LYZ), total immunoglobulin (total Ig), respiratory burst activity (RBA), total protein, and phagocytosis (PHA) (P < 0.05). Moreover, compared with the control group, supplementation could significantly decrease glucose (GLU) and cortisol (CORT), alanine transaminase (ALT), lactate dehydrogenase (LDH), aspartate transaminase (AST), and alkaline phosphatase (ALP) (P < 0.05). After the challenge, FW and WG in all treated challenge groups were significantly improved compared to the control group (P < 0.05). FCR showed a significant decrease in all treated challenged groups compared to the control group (P < 0.05). However, malondialdehyde, CAT, GPx, SOD, LYZ, complement activity (C3 and C4), total Ig, RBA, peroxidase, and PHA in challenged treated groups were significantly increased compared to the control group (P < 0.05). All treated challenged groups showed lower ALT, LDH, AST, ALP, GLU, and CORT levels than the control group (P < 0.05). The experiment herein successfully demonstrated that dietary ME stimulated fish growth, antioxidant status, and immune responses in crowding conditions and can be recommended as beneficial feed additives for rainbow trout.

The Effects of Laurencia caspica Algae Extract on Hemato-Immunological Parameters, Antioxidant Defense, and Resistance against Streptococcus agalactiae in Nile tilapia (Oreochromis niloticus)

Natural immune stimulants are among the most effective chemicals for boosting immunity and fish welfare. This study aims to investigate the effects of red macroalgae extract (Laurencia caspica) on hematological, immunological, antioxidant, biochemical, and disease resistance against S. agalactiae in Nile tilapia for 50 days. For this purpose, fishes were assigned to four dietary treatments group in which the base meal was supplemented with 0.5%, 1%, and 2% of L. caspica extract. On days 25 and 50 of the experiment, samples were taken to investigate the hematological, immunological, biochemical, and antioxidant parameters. The white blood cells (WBCs), hemoglobin, and neutrophils significantly increased after 50 days of feeding with the L. caspica extract, but until the 25th day, no significant difference was observed among the treatments except for hemoglobin. Immunological parameters (including Immunoglobulin M [IgM] and complement 3 [C3]) were significantly higher in treated groups compared to control both 25 days and 50 days posttreatment. However, on the 25th day, no significant difference was noticed between treatments and control in the case of lysozyme activity. Alkaline phosphatase (ALP) and alanine aminotransferase (ALT) considerably increased in comparison to the control group on the 50th day, but no significant difference was observed on the 25th day. In addition, feeding with L. caspica significantly increased the antioxidant enzyme activities on the 25th day (L. caspica 1% and 2% in peroxidase [POD] and superoxide dismutase [SOD] in all groups) and 50th day (catalase [CAT], SOD and L. caspica 1% and 2% in POD) in the spleen. The survival rate of fish challenged with Streptococcus agalactiae was considerably greater than the control group. Finally, it can be concluded that L. caspica extract is an immunological stimulant that induces fish resistance to S. agalactiae.

Autochthonous Bacillus subtilis and Enterococcus faecalis improved liver health, immune response, mucosal microbiota and red-head disease resistance of yellow drum (Nibea albiflora)

Yellow drum (Nibea albiflora), a commercially important fish species in the coastal regions of southeast China, is highly susceptible to red-head disease caused by Vibrio harveyi B0003. Probiotics have been shown to enhance disease resistance in fish, but whether commensal probiotics could improve of the resistance to red-head disease in yellow drum and possible mechanisms has yet not been reported. A six-week feeding trial was conducted to investigate the red-head disease resistance potentials of five probiotic candidates (Bacillus megaterium B1M2, B. subtilis B0E9, Enterococcus faecalis AT5, B. velezensis DM5 and B. siamensis B0E14), and the liver health, serum and skin immunities, gut and skin mucosal microbiota of yellow drum were determined to illustrate the possible mechanisms. The results showed that autochthonous B. subtilis B0E9 and E. faecalis AT5 (particularly E. faecalis AT5, P < 0.05) effectively improved red-head disease resistance in yellow drum. Furthermore, B. subtilis B0E9 and E. faecalis AT5 (particularly E. faecalis AT5) efficiently improve liver health by improving liver morphology and decreasing serum glutamic oxaloacetic transaminase and glutamic propylic transaminase activities pre and post challenged with V. harveyi B0003 (P < 0.05). B. subtilis B0E9 and E. faecalis AT5 led to significant improvement (P < 0.05) in the serum complement 3 content (un-detected after challenged with V. harveyi B0003), lysozyme activity and skin mucosal immunity (such as IL-6, IL-10 and lysozyme expression) pre and post challenged with V. harveyi B0003, which was generally consistent with the cumulative mortality after challenged with V. harveyi B0003. This induced activations of serum and skin mucosal immunities were consistent with the microbiota data showing that B. subtilis B0E9 and E. faecalis AT5 modulated the overall structure of intestinal and skin mucosal microbiota, and in particular, the relative abundance of potentially pathogenic Achromobacter decreased while beneficial Streptococcus, Rothia, and Lactobacillus increased in fish fed with B. subtilis B0E9 and E. faecalis AT5. Overall, autochthonous B. subtilis B0E9 and E. faecalis AT5 (particularly E. faecalis AT5) can improve liver health, serum and skin immunities (especially up-regulated lysozyme activity and inflammation-related genes expression), positively shape gut and skin mucosal microbiota, and enhance red-head disease resistance of yellow drum.

Micro-/bio-/nano-/syn-encapsulations and co-treatments of bioactive microbial feed supplementation in augmenting finfish health and aquaculture nutrition: a review

Finfish and fish products are globally the most acknowledged health-promoting foods. The rising incidence of pathogenic and disease outbreaks have had a sizeable impact on aquaculture. Microbial supplementation of food in the form of probiotics, prebiotics, and their controlled release combinations (=co-encapsulations) as 'synbiotics' is noted for its significant biotherapeutic and health benefits. Supplementation of probiotic microbial feed additives in the fish diet claims to improve fish health by modulation of resident intestinal microbiota and by introducing healthy microbiota procured from an exogenous source, capable of combating pathogens, improving nutrient uptake, assimilation, growth as well as survival. Prebiotics are selectively digestible substrates beneficially used by host gut microbes to enhance probiotic effects. Formulating a fish diet with augmented probiotics and prebiotic microbial bio-supplements can ensure a sustainable alternative for establishing fish health in a naturally susceptible aquaculture scenario. Micro-encapsulation, co-encapsulation, and nano-encapsulation are novel strategies of biotechnical interventions in functional feeds for finfish. These aim to improve probiotic persistence, survivability, and efficacy in commercial formulations during probiotic transit through the host-gut environment. This review discusses the importance of co-treatment and encapsulation strategies for improving probiotic and prebiotic potential in aquafeed formulations, reliably improving finfish health and nutritional returns from aquaculture, and, consequently, for consumers.

Biotherapeutic microbial supplementation for ameliorating fish health: developing trends in probiotics, prebiotics, and synbiotics use in finfish aquaculture

Nutrition demands in aquaculture can be realized through quality aquafeeds as compounded diets that contribute to the growth and health of aquaculture species. Functional additives in feed, notably probiotics, prebiotics, and their admixture synbiotics, have been recently recognized for their biotherapeutic role as immunostimulants capable of conferring disease resistance, stress tolerance, and gastrointestinal health; counteracting the negative effects of anti-nutrients, pathogenic prevalence, and antimicrobials in finfish aquaculture. Formulated diets based on probiotics, prebiotics, and as a supplemental combination for synbiotics can significantly influence fish gut microbiomes, establishing the modalities of microbial dynamics to maximize host-associated benefits. These microbial functional-feed supplements are acclaimed to be biocompatible, biodegradable, and safe for dietary consumption as well as the environment. In fed fish aquaculture, prebiotic appended probiotic diet 'synbiotic' has propounded larger attention for its additional health and nutritional benefits. Synbiotic, prebiotic, and probiotic usage as functional feeds for finfish aquaculture thus provides promising prospects. Developing trends in their intended application are reviewed here forth.

Bioactive immunostimulants as health-promoting feed additives in aquaculture: A review

Bioactive immunostimulants could be derived from different sources like plants, animals, microbes, algae, yeast, etc. Bioactive immunostimulants are the most significant role to enhance aquatic production, as well as the cost of this method, which is effective, non-toxic, and environment-friendly. These immunostimulants are supportive to increase the immune system, growth, antioxidant, anti-inflammatory, and disease resistance of aquatic animals' health and also improve aquatic animal feed. Diseases are mainly targeted to the immune system of aquatic organisms in such a way that different processes of bioactive immunostimulants progress are considered imperative techniques for the development of aquaculture production. Communicable infections are the main problem for aquaculture, while the mortality and morbidity connected with some outbreaks significantly limit the productivity of some sectors. Aquaculture is considered the mainly developing food production sector globally. Protein insists is an important issue in human nutrition. Aquaculture has been an exercise for thousands of years, and it has now surpassed capture fisheries as the most vital source of seafood in the world. Limited study reports are available to focal point on bioactive immunostimulants in aquaculture applications. This review report provides information on the nutritional administration of bioactive immunostimulants, their types, functions, and beneficial impacts on aquatic animals' health as well as for the feed quality development in the aquaculture industry. The scope of this review combined to afford various kinds of natural derived bioactive molecules utilization and their beneficial effects in aquaculture applications.

Use of Probiotic Bacteria and Bacteriocins as an Alternative to Antibiotics in Aquaculture

In addition to their use in human medicine, antimicrobials are also used in food animals and aquaculture, and their use can be categorized as therapeutic against bacterial infections. The use of antimicrobials in aquaculture may involve a broad environmental application that affects a wide variety of bacteria, promoting the spread of bacterial resistance genes. Probiotics and bacteriocins, antimicrobial peptides produced by some types of lactic acid bacteria (LAB), have been successfully tested in aquatic animals as alternatives to control bacterial infections. Supplementation might have beneficial impacts on the intestinal microbiota, immune response, development, and/or weight gain, without the issues associated with antibiotic use. Thus, probiotics and bacteriocins represent feasible alternatives to antibiotics. Here, we provide an update with respect to the relevance of aquaculture in the animal protein production sector, as well as the present and future challenges generated by outbreaks and antimicrobial resistance, while highlighting the potential role of probiotics and bacteriocins to address these challenges. In addition, we conducted data analysis using a simple linear regression model to determine whether a linear relationship exists between probiotic dose added to feed and three variables of interest selected, including specific growth rate, feed conversion ratio, and lysozyme activity.

Effects of Dietary Lactiplantibacillus plantarum subsp. plantarum L7, Alone or in Combination with Limosilactobacillus reuteri P16, on Growth, Mucosal Immune Responses, and Disease Resistance of Cyprinus carpio

Skin mucosal lymphoid tissues of fish are the first line of defence against pathogen invasion. We investigated the effects of Lactiplantibacillus plantarum subsp. plantarum L7, singularly or in combination with Limosilactobacillus reuteri P16, on mucosal immunity and diseases resistance of carp Cyprinus carpio. C. carpio (average weight: 26.28 ± 1.02 g) were divided into five experimental groups. Fish in each group were fed with one of the following potential probiotic-supplemented diets: control (0 - basal diet), D1 (10⁷ CFU/g L7), D2 (10⁸ CFU/g L7), D3 (10⁹ CFU/g L7), and D4 (10⁸ CFU/g L7 + 10⁸ CFU/g P16). Eight weeks post-feeding, growth performance was higher in D4, with a final weight gain of 67.18 ± 1.47 g. Results showed a significantly higher skin mucosal lysozyme, alkaline phosphatase, mucus protein level, superoxide dismutase, and catalase activities in D2 and D4 compared to the control. However, potential probiotics had no significant effect on skin mucosal immunoglobulin level. Skin mucus of D4 exhibited stronger inhibition zones against pathogenic bacterial strains. Moreover, digestive enzyme activities (protease, lipase) were highest in D4. Intesinal lactic acid bacterial counts of fish fed combind probiotics (i.e. D4) was significantly higher than the control. Further, supplementation of potential probiotics altered the expression of IL-1β, TNF-α, and IL-10 cytokines. Fish from D4 exhibited significantly higher relative post-challenge survival (69.7%) against Aeromonas hydrophila, followed by D2 (66.67%). Therefore, the inclusion of L. plantarum subsp. plantarum L7 at 10⁸ CFU/g or in combination with L. reuteri P16 could enhance the growth performance, mucosal immune responses, and disease resistance of C. carpio.

Protective effects of non-encapsulated and microencapsulated Lactobacillus delbrueckii subsp. bulgaricus in rainbow trout (Oncorhynchus mykiss) exposed to lead (Pb) via diet

The present study was designed to investigate the effects of dietary non-encapsulated and microencapsulated Lactobacillus delbrueckii subsp. bulgaricus on growth performance, intestinal enzymatic activities, antioxidant capacity and hepato-biochemical parameters of rainbow trout before or after exposure to lead via diet. Fingerling fish (16 ± 4 g) were divided into four groups: negative control (NC), positive control (PC), probiotic (PR) and encapsulated probiotic (EN-PR). During the pre-exposure period (days 0-45), fish in the NC and PC groups received the basal diet, whereas fish in the PR and EN-PR groups were fed with basal diet containing 108 CFU g−1 feed of non-encapsulated and microencapsulated probiotic, respectively. During the exposure period (days 46-66), the fish in the probiotic and PC groups were co-treated with 500 μg g−1 feed of lead nitrate. Blood, liver and gut samples were taken at days 0, 45, 52, 59 and 66. The results revealed that growth performance and intestinal enzymatic activities were significantly (p< 0.05) improved in the probiotic groups compared to the NC group (day 45). Dietary exposure to lead resulted in the highest levels of liver aspartate aminotransferase (AST), liver alkaline phosphatase (ALP) and serum malondialdehyde (MDA), and the lowest activities of serum superoxide dismutase (SOD) and catalase (CAT) in the PC group (day 66). The levels of liver ALP were significantly (p< 0.05) lower in the probiotic groups compared to the NC and PC groups prior to and after exposure to dietary lead. Serum levels of total protein, albumin, SOD, CAT and glutathione (GSH) were significantly increased in fish fed with both non-encapsulated and microencapsulated probiotics (p< 0.05). However, microencapsulated probiotic showed the greatest potential for alleviation of the disturbed activities of intestinal and hepatic enzymes, and improvement of serum biochemical and antioxidant parameters. Our findings suggest that L. delbrueckii subsp. bulgaricus, particularly in the microencapsulated form, can be used as a potential probiotic to protect rainbow trout from dietborne lead toxicity.

Probiotics in Fish Nutrition—Long-Standing Household Remedy or Native Nutraceuticals?

Over the last decades, aquaculture production increased rapidly. The future development of the industry highly relies on the sustainable utilization of natural resources. The need for improving disease resistance, growth performance, food conversion, and product safety for human consumption has stimulated the application of probiotics in aquaculture. Probiotics increase growth and feed conversion, improve health status, raise disease resistance, decrease stress susceptibility, and improve general vigor. Currently, most probiotics still originate from terrestrial sources rather than fish. However, host-associated (autochthonous) probiotics are likely more persistent in the gastrointestinal tract of fish and may, therefore, exhibit longer-lasting effects on the host. Probiotic candidates are commonly screened in in vitro assays, but the transfer to in vivo assessment is often problematic. In conclusion, modulation of the host-associated microbiome by the use of complex probiotics is promising, but a solid understanding of the interactions involved is only in its infancy and requires further research. Probiotics could be used to explore novel ingredients such as chitin-rich insect meal, which cannot be digested by the fish host alone. Most importantly, probiotics offer the opportunity to improve stress and disease resistance, which is among the most pressing problems in aquaculture.

Combined effects of enzymes and probiotics on hemato-biochemical parameters and immunological responses of juvenile Siberian sturgeon (Acipenser baerii)

A 10-week feeding trial was run to investigate the separate and simultaneous effects of exogenous enzymes (Enz), probiotics (Pro), and Pro-Enz mixtures on the hematology indices, serum biochemical parameters, and innate-immunity status of juvenile Siberian sturgeon. The fish (138.06 ± 3.64 g) were randomly dispersed into 12 tanks (20 individuals per tank) and fed with Enz (Phytase, protease, and xylanase), Pro (Pediococcus pentosaceus and Lactococcus lactis), and Pro-Enz cocktail. At the end of the feeding bioassay, the highest values of red blood cell count, hemoglobin concentration, hematocrit level, and lymphocyte percentage followed by the lowest neutrophil percentage were obtained in Pro-Enz treatment (P < 0.05). Despite a significantly lower level of alkaline phosphatase in the fish fed with Pro supplemented diet (P < 0.05), no significant difference was found in the serum level of alanine aminotransferase and aspartate aminotransferase among the experimental groups (P > 0.05). Total protein content was significantly upregulated in serum and skin mucus samples from those fed with supplemented diets compared to the control group (P < 0.05). In both serum and skin mucus samples, higher immune responses in terms of lysozyme activity, immunoglobulin M, total protein was seen in Pro-Enz treatment compared to the control group followed by the serum complement components (P < 0.05). The results indicate that the combinational supplementation of Siberian sturgeon diet with the exogenous enzymes and probiotics modulates the physiometabolic responses and innate immune system to a higher grade than their individual supplementation.

Comparative study on the effect of dietary β-carotene and phycocyanin extracted from Spirulina platensis on immune-oxidative stress biomarkers, genes expression and intestinal enzymes, serum biochemical in Nile tilapia, Oreochromis niloticus

The current trial investigated the roles of β-carotene and phycocyanin extracted from Spirulina platensis on growth, serum biochemical, digestive enzymes, antioxidant defense, immune responses, and immune gene expression in Nile tilapia (Oreochromis niloticus). Fish (1.52 ± 0.10 g) were randomly stocked to three treatments with three replicates (12 fish per replicate) in nine aquaria (60 L glass aquarium for each), and reared for 70-days. Three tested diets were formulated to be isonitrogenous and isolipidic, and were offered for experimental fish until ad-libitum three times daily at 09:00 a.m., 11.00 a.m. and 3:00 p.m. The first diet (control) was without supplementation. About 50 mg β-carotene and 50 mg phycocyanin kg^-1 were supplemented to the other experimental diets, respectively. Results indicated that feed intake was not (P > 0.05) differ among experimental diets. Compared to control diet wight gain and specific growth rate were significantly (P < 0.05) in fish fed diet containing β-carotene, while, the highest weight gain and the best FCR were detected in phycocyanin diet. Survival fish among treatments was significantly (P < 0.05) differ and the highest survival rate was showed in fish fed diet supplemented with phycocyanin. Either β-carotene or phycocyanin significantly (P < 0.05) improved the intestinal digestive enzymes compared with control diet, where the highest values of chymotrypsin, trypsin, lipase and amylase were noticed in fish fed phycocyanin. Diets supplemented with β-carotene and phycocyanin significantly (P < 0.05) improved hematology parameters contents compared with to the control diet, and the best contents were detected in fish fed diet supplemented with phycocyanin. The highest significant (P < 0.05) phagocytic, lysozyme, immunoglobulin M (IgM), superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx) and total antioxidant capacity (T-AOC) activities were recorded in diet supplemented with phycocyanin. The transcripts of interferon gamma and interleukin 1β genes were (P < 0.05) up-regulated in the liver of fish fed diet supplemented with β-carotene and phycocyanin, but expression of HSP70 gene down-regulated in fish fed β-carotene and phycocyanin containing diet compared control. The highest gene expression of the interferon gamma and interleukin 1β was observed in fish fed phycocyanin.

Bacteriome Structure, Function, and Probiotics in Fish Larviculture: The Good, the Bad, and the Gaps

Aquaculture is the fastest-growing sector in food production worldwide. For decades, research on animal physiology, nutrition, and behavior established the foundations of best practices in land-based fish rearing and disease control. Current DNA sequencing, bioinformatics, and data science technologies now allow deep investigations of host-associated microbiomes in a tractable fashion. Adequate use of these technologies can illuminate microbiome dynamics and aid the engineering of microbiome-based solutions to disease prevention in an unprecedented manner. This review examines molecular studies of bacterial diversity, function, and host immunitymodulation at early stages of fish development, where microbial infections cause important economic losses. We uncover host colonization and virulence factors within a synthetic assemblage of fish pathogens using high-end comparative genomics and address the use of probiotics and paraprobiotics as applicable disease-prevention strategies in fish larval and juvenile rearing. We finally propose guidelines for future microbiome research of presumed relevance to fish larviculture.

Effects of single or conjoint administration of lactic acid bacteria as potential probiotics on growth, immune response and disease resistance of snakehead fish (Channa argus)

Lactic acid bacteria (LAB) has been documented to promoting growth, enhancing immunity and disease resistance. In this study, we aimed to evaluate the single or conjoint effects of Lactococcus lactis L19 (Genbank: MT102745.1) and Enterococcus faecalis W24 (Genbank: MT102746.1) isolated from the intestine of Channa argus (C. argus) on growth performance, immune response and disease resistance of C. argus. A total of 720 apparently healthy C. argus (9.50 ± 0.03 g) were randomly divided into four equal groups. Fish were fed with a basal diet (CK) supplemented with L. lactis (L19), E. faecalis (W24), and L. lactis L19 + E. faecalis W24 (L + W) at 1.0 × 10⁸ cfu/g basal diet for 56 days. After feeding, the final body weight (FBW), weight gain (WG), feed efficiency ratio (FER), specific growth rate (SGR) and protein efficiency ratio (PER) had significantly increased (p < 0.05), especially with L19. The results indicated that single or conjoint administration of LAB as potential probiotics can induce high levels of IgM, ACP, AKP, LZM, C3 and C4 activity in serum, which may effectively induce humoral immunity, and L19 induce even higher levels. Meanwhile, when compared to CK group, the results of qPCR showed that LAB administration significantly up-regulated (p < 0.05) the expression of IL-1β, IL-6, IL-10, TNF-α, IFN-γ, HSP70, HSP90, TGF-β in the spleen, head kidney, gill, liver and intestine of C. argus. After challenge with Aeromonas veronii, the survival rates in all LAB-fed groups were significantly higher (p < 0.05) than that of the CK group, and the L19 group showed the highest (63.3%) disease resistance. Our data indicated that L. lactis L19 and E. faecalis W24, as a feed additive at 1.0 × 10⁸ cfu/g feed, could promote growth performance, enhance immune response and disease resistance of C. argus, with greatest effects in fish fed L. lactis L19 for 56 days. Hence, these LAB additives could be used as promising probiotics for C. argus. L19 was more effective than W24 or the mixture of the two for promoting growth performance, enhancing immune response and disease resistance of C. argus.