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This study was carried out to evaluate the potential antibacterial and immunomodulatory effects of the dietary acidifier propionic acid (PA) when given alone or in combination with oxytetracycline (OTC) on Nile tilapia ( Oreochromis niloticus ). Apparently healthy O. niloticus ( n =  240; 52 ± 3.75 g) were randomly allocated into four equal groups ( n =  60/group): control group fed a basal diet alone and the other three groups fed basal diets supplemented with either PA (200 mg /kg of diet, PA group) or OTC (500 mg/kg of diet, OTC group) alone or in combination (PA + OTC group). Each group was subdivided into two subgroups ( n =  30/subgroup, each subgroup had triplicate of 10 fish); subgroup (A) was used to evaluate the antibacterial effects with the aforementioned 2 weeks feeding regime, and subgroup (B) was used to evaluate the immunomodulatory effects against Aeromonas hydrophila infection with similar 2 weeks feeding regime. Among the four groups, PA + OTC group showed the highest significant ( p  < 0.0001) antibacterial activity as indicated by widest inhibition zones against A. hydrophila and lowest total gastrointestinal bacterial counts. Additionally, this group had the best immunomodulatory effect as noticed by a significant ( p  < 0.05) increase in total serum protein, globulin, IgM, phagocytic activity and index, lysosome activity, and significant ( p  < 0.05) upregulation in the expression levels of immunity-related genes ( MHC I, MHC IIA, MHC IIB, Tlr7, IgM heavy chain , TNFα , and IL1β ) in head-kidney. Notably, the combined dietary PA and OTC improved the hematological parameters and reduced the oxidative damage of hepatopancreas and head-kidney induced by OTC. This data suggests dietary PA as potential adjuvant to OTC in O. niloticus diets to get maximal antibacterial and immunomodulatory effects.

This research aimed to explore the effect of Phyllanthus emblica powder on the growth performance, blood hematology, body composition, serum biochemistry, organ histology, gene expression and resistance of Nile Tilapia ( Oreochromis niloticus ) against Aspergillus flavus . A total of 240 fish (30.5 ± 2.0 g) were distributed in 12 ponds with 20 fish per pond and fed a basal diet supplemented with 0, 1%, 2% and 3% of P. emblica powder for 60 days. A challenge experiment was performed at the end of the trial. All supplemented groups showed better growth performance (final body weight, weight gain, and specific growth rates) ( P  < 0.05), while feed intake did not affect ( P  > 0.05). The feed conversion ratio enhanced by the inclusion of dietary P. emblica ( P  < 0.05). In terms of body composition, crude lipids decreased, while ash percentages increased after fish were fed with P. emblica ( P  < 0.05). Liver function decreased significantly, while protein fraction, blood hematology and digestive enzymatic profile (amylase, and lipase) were significantly increased in all treated groups. Fish fed with P. emblica exhibited a higher survival rate and increased resistance to A. flavus compared to the control diet. Diets containing P. emblica improved the histoarchitecture of hepatopancreatic and intestine of Nile Tilapia. The inclusion of P. emblica significantly upregulated the expression of CC chemokine , IL-1β , IL-8 , SOD , and GPx genes, with a gradual increase in P. emblica levels in the diet ( P  < 0.05). In conclusion, dietary supplementation with P. emblica powder may serve as an effective strategy for promoting growth and acting as an immunostimulant in Nile Tilapia aquaculture.

Nile tilapia, is a crucial fish for warmwater aquaculture globally and plays a key role in food security. The experiment’s goal was to ascertain the actual effects of lemongrass and/or Arthrospira platensis (A. platensis) on Oreochromis niloticus (O. niloticus) growth. Along with liver and kidney functioning, some organ histopathology, and the expression of genes linked to immunity in liver tissue both before and after an infection with Aeromonas hydrophila (A. hydrophila) . There were four diets created: with the first serving as a control group and being additive-free, while the second included 7.5 g kg − 1 of diet of A. platensis , the third included 200 mg kg − 1 of diet of lemongrass ( Cymbopogon citratus ), and the fourth group included lemongrass and A. platensis . The results of the growth trail were significantly higher in the treatment groups, especially with A. platensis treatment. However, the results of the biochemistry and immunological assay were pronounced with improved intestinal morphometry in the combination groups without pathological lesions. Moreover, the antioxidant and proinflammatory cytokine gene expressions improved with the treatments used. After experimental challenges, the results of the treatment groups showed the immunomodulatory effects of A. platensis and lemongrass oil against A. hydrophila infection. Thus, A. platensis alone or with lemongrass improved growth performance before experimental infection. After experimental infection, they decreased mortality rate and pathological lesions in liver and spleen and improved biochemical parameters and antioxidant and proinflammatory cytokine gene expression.

The intestinal microbiota and morphology of tilapia (Oreochromis niloticus) were investigated after the application of a multi-species probiotic containing Lactobacillus reuteri, Bacillus subtilis, Enterococcus faecium and Pediococcus acidilactici (AquaStar® Growout). Tilapia (55.03 ± 0.44 g) were fed either a control diet or a probiotic diet (control diet supplemented with AquaStar® Growout at 5 g kg⁻¹). After four and eight weeks, culture-dependent analysis showed higher levels of lactic acid bacteria (LAB), enterococci and Bacillus spp. in the mucosa and digesta of fish fed AquaStar® Growout. At week four, polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) revealed a higher similarity within the probiotic fed replicates than replicates of the control group; after eight weeks, the compositional dissimilarity of the microbiome profiles between the groups was greater than the dissimilarities within each group (P < 0.05). High-throughput sequencing revealed that the probiotic treatment significantly reduced the number of operational taxonomic units and species richness in the digesta. Significantly higher proportions of reads belonging to Proteobacteria and Cyanobacteria were detected in the control group whereas the probiotic-fed fish displayed a significantly higher abundance of reads assigned to the Firmicutes (which accounted for >99 % of reads). Bacillus, Cetobacterium and Mycobacterium were the dominant genera in the digesta of control fish whereas Bacillus, Enterococcus and Pediococcus were the largest constituents in probiotic-fed fish. The addition of AquaStar® Growout to tilapia diets led to increased populations of intraepithelial leucocytes, a higher absorptive surface area index and higher microvilli density in the intestine. These data suggest that AquaStar® Growout can modulate both the intestinal microbiota and morphology of tilapia.

The impacts of oregano essential oil and sodium butyrate on the growth performance, hematological, biochemical, immunological, antioxidative, and gene expression profiles of Nile tilapia ( Oreochromis niloticus ) fingerlings were examined in this study. One hundred eighty healthy fingerlings (16.00 ± 2.00 g) were acclimated and accidentally divided into three groups, each further split into three replicates. The groups were fed a basal diet (control) or diets supplemented with 0.5% and 1% oregano essential oil and sodium butyrate for eight weeks (The feed additives were administered continuously throughout an 8-week trial period, simulating a practical feeding strategy that would be feasible during high-risk periods (e.g., post-handling stress, seasonal disease outbreaks). Fish fed the supplemented diets demonstrated significantly greater growth performance, with the oregano 1% + sodium butyrate 1% group achieving the highest final body weight (36.91 ± 0.66 g) and lowest feed conversion ratio (1.32 ± 0.04). Hematological indices, including RBC count, Hb, and PCV, were substantially improved. Biochemical analysis revealed reduced ALT, AST, urea, and creatinine levels alongside elevated total protein and globulin concentrations in treated groups. Immunological and antioxidative parameters, such as WBC count, phagocytic activity, SOD, and GPX, showed significant enhancements, particularly in the oregano 1% + sodium butyrate 1% group. Gene expression analysis exposed upregulation of immune-related (TNF-α, IL-1β) and antioxidative (SOD, GPX) genes in supplemented groups, highlighting their role in enhancing health and stress responses. Post Aeromonas hydrophila infection, the supplemented groups exhibited improved immunity, antioxidative status, and survival. These findings suggest that dietary supplementation with oregano essential oil and sodium butyrate, particularly at 1% inclusion, effectively enhances growth, health status, immunity, and gene expression in Nile tilapia.

The heavy metal cadmium (Cd) is a hazardous pollutant that exerts various toxic effects on aquatic animals. The biomagnifying effects of this non-essential element in the food chain also pose threats to human health. In this study, the protective effect of a dietary probiotic supplementation, Lactobacillus plantarum CCFM8610, on the intestinal microbiota and physiological conditions of Nile tilapia ( Oreochromis niloticus ) exposed to waterborne Cd was evaluated. Two hundred fish were divided into four groups, i.e., control, probiotic-only, Cd-only and Cd-plus-probiotic. The fish were exposed to waterborne Cd at a level of 1 mg L −1 for 4 weeks and the probiotic was administered twice daily at 10 8  CFU g −1 in the fish diet. Waterborne Cd exposure caused a profound decline in the gut microbial diversity and marked alterations in the composition of the microbiota. Dietary supplementation with L. plantarum CCFM8610 reversed the changes in the intestinal microbiota composition in the Cd-exposed fish and reduced the abundance of Flavobacterium and Pseudomonas . Compared with the Cd-only group, the probiotic treatment significantly promoted growth performance and prevented the death of the Cd-exposed fish. L. plantarum CCFM8610 supplementation also decreased Cd accumulation and alleviated oxidative stress in the tissues, and reversed the alterations in hemato-biochemical parameters in the blood of fish. The results suggest that L. plantarum CCFM8610 can be considered a safe dietary supplement for the prevention of Cd-exposure-induced problems in aquaculture and food safety.

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

Aflatoxin B1 (AFB1) is a plant-origin toxin that could induce oxidative stress in fish. The micromineral selenium (Se) possesses well-documented antioxidant properties. To assess the ameliorative effects of SeNPs (1 mg/kg fish feed) on oxidative stress induced by AFB1 (500 μg/kg fish feed), Nile tilapia (32.2±1.7 g body weight) were distributed randomly and even in six groups for 8-week feeding trial. Live enzymes, AST, ALT, and ALP levels were increased in the serum of fish fed AFB1-contaminated diet, and the addition of SeNPs could restore normal values compared to the control. The gene expression of antioxidant enzymes, superoxide dismutase (SOD) enzyme and catalase (CAT) enzyme, and DNA fragmentation were significantly increased in response to aflatoxin exposure, while dietary SeNPs could mitigate the generated oxidative stress. The innate immunity, serum antibacterial activity (SAA), oxidative burst activity (OBA), phagocytic activities (PA and PI), and gene expression of cytokines (interleukin (IL)-1β, heat shock protein70 (Hsp), and tumor necrosis factor (TNF)-α) revealed a status of immunosuppression in Nile tilapia fed on AFB1-contaminated diet. These findings showed that fish became more vulnerable to Streptococcus agalactiae infection with a high mortality rate while dietary SeNPs provided a high relative protection level (RPL). From the obtained findings, SeNPs could mitigate the oxidative stress induced by feeding the AFB1 diet and could boost the immunity of stressed Nile tilapia.

Probiotic production in commercial culture media is expensive, so, it is necessary to design culture media based on “low-cost” components like agro-industrial by-products. Therefore, this study aimed to design an agro-industrial by-product-based culture media using whey, sugarcane molasses, and palm kernel cake as components to produce Lactococcus lactis A12, Priestia megaterium M4, and Priestia sp. M10 isolated from Nile tilapia ( Oreochromis niloticus ) associated gut microbiota. Higher bacterial concentrations were achieved at high whey concentrations and low concentrations of sugarcane molasses and palm kernel cake (PKC) using agitation. The optimal conditions were whey, 3.84% w/v; sugarcane molasses, 7.39% w/v; PKC, 0.77% w/v; and agitation speed, 75 RPM. Bacterial growth under optimal conditions was compared to that in commercial Brain–Heart Infusion (BHI) broth. L. lactis A12 showed similar growth in the optimal media and BHI. The estimated cost of the culture media based on component prices was USD $ 3.01/L, which is 86.93% lower than BHI broth (USD $ 23.04/L). It was possible to design a “low-cost agro-industrial by-product-based culture media to produce L. lactis A12 and the two Priestia species under monoculture conditions.

The aquaculture industry has been growing rapidly over the past few decades to meet future animal protein demands. However, intensive aquaculture industry faces challenges such as growth abnormalities, high mortality rates, water quality and intestinal health deterioration. Administering probiotics can serve as a nutritional strategy to enhance the immune system and growth performance of fish influxes of gut microbiota. This study aimed to evaluate the impact of two dietary probiotic strains L . mesenteroides and L . lactis on the growth performance, immunity, and gut microbiota of Nile tilapia ( Oreochromis niloticus ). Fish were fed with basal and experimental diet supplemented by both L . mesenteroides and L . lactis bacteria at 10 6 cell/g for 8 weeks. Feeding a combination of L . mesenteroides and L . lactis resulted in significant improvements in feed utilization parameters (PER and FER) (P < 0.001), alternative complement pathway activity, intestinal lactic acid bacteria count (P < 0.012), mucus secretion (P < 0.002) and peroxidase activity (P < 0.001) compared to the control groups. Serum lysozyme activity also exhibited a significant increase in the L . mesenteroides and L . lactis dietary group (P < 0.011) compared to the control and single probiotic supplemented diet groups. Furthermore, Nile tilapia fed the L . mesenteroides and L . lactis supplemented diet showed enhanced growth performance metrics (weight gain, final weight and specific growth rate) compared to those fed control and single probiotic supplemented diets (P < 0.022). Additionally, superoxide dismutase activity was significantly elevated in the L . mesenteroides and L . lactis supplemented diet groups compared to the control and single L . mesenteroides supplemented diet groups (P < 0.017). These findings strongly indicate that a dietary combination of L . mesenteroides and L . lactis probiotics could function as a beneficial immunostimulant feed supplement in Nile tilapia aquaculture.