Effects of dietary supplementation of Lactobacillus plantarum and Bacillus subtilis on growth performance, survival, immune response, antioxidant capacity and digestive enzyme activity in olive flounder (Paralichthys olivaceus)

The alleviative effect of Bacillus subtilis-supplemented diet against Vibrio cholerae infection in Nile tilapia (Oreochromis niloticus)

Bacterial illness causes detrimental impacts on fish health and survival and finally economic losses for the aquaculture industry. Antibiotic medication causes microbial resistance, so alternative control strategies should be applied. In this work, we investigated the probiotic-medicated diet as an alternative control approach for antibiotics in treating Vibrio cholerae infection in Nile tilapia (Oreochromis niloticus). One hundred eighty fish (50 ± 2.5 g Mean ± SD) were allocated into six groups in glass aquariums (96 L) in triplicate for 10 days. Groups 1 (G1), G2, and G 3 were intraperitoneally (IP) injected with 0.5 mL sterilized tryptic soy broth and fed on a basal diet, basal diet contained B. subtilis (BS) (1 × 10 5 CFU/ kg-1 diet), and basal diet contained trimethoprim-sulfamethoxazole (TMP-SMX) (1.5 g/kg-1 diet), respectively. Additionally, G4, G5, and G6 were IP challenged with 0.5 mL of V. cholerae (1.5 × 107 CFU) and received the same feeding regime as G 1 to 3, respectively. The results exhibited that the V. cholera-infected fish exhibited skin hemorrhage, fin rot, and the lowest survival (63.33%). Additionally, lowered immune-antioxidant biomarkers (white blood cells count, serum bactericidal activity, phagocytic activity, phagocytic index, and lysozymes) with higher lipid peroxidation marker (malondialdehyde) were consequences of V. cholerae infection. Noteworthy, fish-fed therapeutic diets fortified with BS and TMP-SMX showed a substantial amelioration in the clinical signs and survival. The BS diet significantly improved (P < 0.05) the immune-antioxidant indices of the infected fish compared to the TMP-SMX diet. The current findings supported the use of a BS-enriched diet as an eco-friendly approach for the control of V. cholerae in O. niloticus.

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.

Microbial inoculums improve growth and health of Heteropneustes fossilis via biofloc-driven aquaculture

Biofloc technology aims to maximize fish farming productivity by effectively breaking down ammonia and nitrite, promoting healthy flocculation, and enhancing the growth and immunity of cultured animals. However, a major limitation in this field is the suitable starter microbial culture and narrow number of fish species that have been tested with the biofloc system. Here, we investigated various microbial inoculum containing beneficial microbes with probiotics, immunostimulatory and flocs development and bioremediation properties would lead to the development of ideal biofloc development. Three treatment groups with different microbial combinations, viz., group 1 [Bacillus subtilis (AN1) + Pseudomonas putida (PB3) + Saccharomyces cerevisiae (ATCC-2601)], group 2 [B. subtilis (AN2) + P. fluorescens (PC3) + S. cerevisiae (ATCC-2601)] and group 3 [B. subtilis (AN3) + P. aeruginosa (PA2) + S. cerevisiae (ATCC-2601)] were used and compared with the positive control (pond water without microbial inoculums) and negative control (clear water: without microbial inoculums and carbon sources) on biofloc development and its characteristic features to improve the water quality and growth of fish. We demonstrated that microbial inoculums, especially group 2, significantly improve the water quality and microbiota of flocs and gut of the test animal, Heteropneustes fossilis. The study further demonstrates that biofloc system supplemented with microbial inoculums positively regulates gut histomorphology and growth performance, as evidenced by improved villous morphology, amylase, protease and lipase activity, weight gain, FCR, T3, T4 and IGF1 levels. The inoculums induced an antioxidative response marked by significantly higher values of catalase (CAT) and superoxide dismutase (SOD) activity. Furthermore, the supplementation of microbial inoculums enhances both specific and non-specific immune responses and significantly elevated levels of immune genes (transferrin, interleukin-1β and C3), and IgM was recorded. This study provides a proof-of-concept approach for assessing microbial inoculums on fish species that can be further utilized to develop biofloc technology for use in sustainable aquaculture.

Characterization of Cetobacterium somerae CPU-CS01 isolated from the intestine of healthy crucian carp (Carassius auratus) as potential probiotics against Aeromonas hydrophila infection

Cetobacterium somerae is a commensal bacterium for many fish species. However, research on C. somerae has been limited so far, and its function and beneficial potential require to be further investigated. The objective of this study was to evaluate the probiotic properties of C. somerae CPU-CS01 isolated from the intestinal contents of crucian carp (Carassius auratus). Hemolytic activity, antibiotic susceptibility, acid tolerance, bile salt tolerance, free radical scavenging, and enzyme production properties were tested for in vitro. Caenorhabditis elegans and zebrafish (Danio rerio) model were used to evaluate the antioxidant and anti-infective effects of C. somerae CPU-CS01 in vivo. Our results showed that C. somerae CPU-CS01 had no hemolytic activity, it produced cellulase, amylase, and survived at low pH (2.0-3.0) and in the presence of bile salts. The cell-free culture supernatant (CFCS) of C. somerae CPU-CS01 possessed DPPH radical, hydroxyl radical, and superoxide anion scavenging activity. C. elegans fed with C. somerae CPU-CS01 were more resistant to hydrogen peroxide-induced oxidative stress and Aeromonas hydrophila infection. In addition, zebrafish-fed diets containing C. somerae CPU-CS01 showed improved survival after A.hydrophila infection. Based on these results, the positive probiotic properties of C. somerae CPU-CS01 isolated from the intestinal contents of crucian carp make it a potential candidate for probiotic.

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

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

The Optimum Lipid Level for the Juvenile Redclaw Crayfish Cherax quadricarinatus: Practical Diets with Soybean Oil as the Lipid Source

As a new species in aquaculture, the lipid nutrition requirement for the juvenile redclaw crayfish Cherax quadricarinatus on a dietary basis on a practical formula needs to be evaluated accurately. In this study, the optimum dietary lipid level was explained by analyzing the growth performance, antioxidant state, lipid metabolism, and gut microbiota of C. quadricarinatus after an eight-week cultivation trial. Six diets with different soybean oil levels (named L0, L2, L4, L6, L8, and L10) were fed to C. quadricarinatus (11.39 ± 0.28 g). The results indicated that the specific growth rate and weight gain of crayfish fed the L4 and L6 diets were significantly higher than those of the other groups (P < 0.05). By the analysis of a second-order polynomial regression model according to growth performance (weight gain rate), the optimum lipid level in a practical diet for juvenile C. quadricarinatus was 9.67%. The survival, condition factor, and hepatosomatic index of crayfish were not significantly affected by dietary oil levels (P > 0.05). As the level of dietary lipids increased, the total antioxidant capacity and glutathione peroxidase activity in serum showed a tendency to rise and then fall and the enzyme activity was highest in crayfish fed the L6 diet. Gut lipase and pepsin activities showed the highest value in crayfish fed the L6 diet. There was no significant difference in acetyl-CoA carboxylase and carnitine palmitoyltransferase-1 contents in crayfish among all the groups (P > 0.05). The relative abundance of Proteobacteria in the phylum and Citrobacter in the genus showed a significant decrease in crayfish of the L10 diet, while the relative abundance of Firmicutes in the phylum markedly increased compared to that of the other groups (P < 0.05). In summary, the results indicated that the 10.39% (L6 diet) dietary lipid level could induce better growth performance, antioxidant ability, and digestive enzyme activity. Most of the fatty acid composition of muscle is not closely related to the fatty acid composition of the diet. Moreover, the composition and diversity of the gut microbiota of C. quadricarinatus were changed by high dietary lipid levels.

Boosted growth performance, immunity, antioxidant capacity and disease resistance of crucian carp (Carassius auratus) by single or in combination dietary Bacillus subtilis and xylo-oligosaccharides

In this study, a total of 420 healthy crucian carp (9.77 ± 0.04 g) were randomly divided into CK, B·S, XOS and B·S + XOS group, and cultured for 8 weeks. Results showed that the dietary Bacillus subtilis (B. subtilis) and xylo-oligosaccharides (XOS) can significantly increased the final weight, weight gain, specific growth rate, feed efficiency, protein efficiency and survival rate of crucian carp. Dietary B. subtilis and XOS can significantly increased the activities of catalase, glutathione, superoxide dismutase and total antioxidant capacity, significantly decreased the contents of malondialdehyde, and significantly increased the activities of alkaline phosphatase, acid phosphatase, lysozyme and the contents of complement component 3,4 and immunoglobulin M in crucian carp serum. In addition, compared with CK group, the expression levels of TGF-β and IL-10 in B·S, XOS and B·S + XOS group were significantly increased, and the expression levels of TNF-α, HSP90, IL-1β, TLR4 and MyD88 were significantly decreased. Supplementation of B. subtilis and XOS can also improve the intestinal tissue morphology of crucian carp. After injection of 1 × 10⁷ CFU/mL Aeromonas hydrophila (A. hydrophila), compared with CK group, the survival rates of the B·S group, the XOS group and the B·S + XOS group were increased by 13.98%, 10.56% and 30.74%, respectively. These results show that dietary B. subtilis and XOS can significantly improve the growth performance, antioxidant capacity, immunity and resistance to A. hydrophila of crucian carp, and the combined effect is better than that of single addition.

The Combined Effects of Propionic Acid and a Mixture of Bacillus spp. Probiotic in a Plant Protein-Rich Diet on Growth, Digestive Enzyme Activities, Antioxidant Capacity, and Immune-Related Genes mRNA Transcript Abundance in Lates calcarifer Fry

A 7-week feeding trial was conducted to evaluate the combined effects of propionic acid (PA, 5 or 10 g/kg) and a multi-strain Bacillus spp. (Bacillus subtilis IS02 (accession no. JN856456) and B. licheniformis IBRC-M 11,319) (1.7 × 10⁷ CFU/g) probiotic in a plant protein source (PP)-rich diet (∼70% of dietary protein derived from PP sources) on performance of Asian sea bass (Lates calcarifer) fry (initial body weight 2.97 ± 0.11 g). In this regard, six isoproteic (∼48%) diets were formulated as follows: a control (without supplementation of the additives); probiotic (only contained Bacillus spp. mixture); 5 g PA/kg diet; 10 g PA/kg diet; probiotic + 5 g PA/kg diet, and probiotic + 10 g PA/kg diet. Specific growth rate in fish fed with 10 g PA/kg (2.84 ± 0.1%) and diets contained blends of probiotic and PA (2.76 ± 0.19% in probiotic + 5 g PA, and 2.79 ± 0.04% in probiotic + 10 g PA) was better than in the control (2.45 ± 0.1%) (P < 0.05). Feed conversion ratio in fish fed with 10 g PA/kg (0.92 ± 0.12) and diets contained blends of probiotic and PA (0.94 ± 0.06 in probiotic + 5 g PA and 0.91 ± 0.02 in probiotic + 10 g PA) was better than in the control (1.24 ± 0.08) (P < 0.05). Digestive enzymes including α-amylase, total alkaline proteases, and bile salt dependent lipase activities improved in fish fed diets contained additives. The activity of glutathione-S-transferase and glutathione reductase enhanced in the liver of fish fed diets contained additives. The relative abundance of lysozyme, interleukin 1β, and insulin-like growth factor-1 genes mRNA transcript showed multifold increase in the liver of fish fed with the 10 g PA/kg and diets contained blends of probiotic and PA (P < 0.05). By considering the above mentioned results, supplementing a PP-rich diet with 10 g PA/kg diet or combination of PA and a mixture of Bacillus spp. probiotic recommended for L. calcarifer.