Modulation of growth performance, antioxidant capacity, non-specific immunity and disease resistance in largemouth bass (Micropterus salmoides) upon compound probiotic cultures inclusion

Effects of Rhodopseudomonas palustris and composite probiotics on growth performance, intestinal health, and non-specific immunity of sea urchin (Strongylocentrotus intermedius)

In recent decades, antibiotics have been widely used in sea urchin aquaculture to prevent diseases and improve water quality. However, their use leads to the emergence of resistant strains and environmental problems. Probiotics can serve as a green and pollution-free alternative. In this study, we mixed probiotics (Rhodopseudomonas palustris) (3 × 108 CFU/mL) and composite probiotics (5 × 108 CFU/mL) in a 1:1 ratio, establishing four supplementation levels: 0 % (FC, control group), 0.5 % (FL group), 1 % (FM group), and 2 % (FH group). At the end of the 50-day experiment, compared to the control group (FC), supplementation with R. palustris and composite probiotics (containing 60.13 % Lactobacillaceae and 20.79 % Acetobacteraceae) in the FL, FM, and FH groups significantly improved the growth performance of sea urchins (Strongylocentrotus intermedius), including final body weight (FBW), weight gain rate (WGR), specific growth rate (SGR), and gonadosomatic index (GSI). Additionally, antioxidant indicators (e.g., total antioxidant capacity (T-AOC), superoxide dismutase (SOD), and catalase (CAT)), immune indicators (e.g., acid phosphatase (ACP), alkaline phosphatase (AKP), and lysozyme (LZM)), and digestive enzyme activity were significantly increased in FM and FH groups. Probiotic supplementation also increased colonization of beneficial bacteria (Rhodobacteraceae) and enhanced microbiota diversity. The FM group, in particular, showed significantly upregulated expression of heat shock protein 70 (HSP70), glutathione peroxidase (GPX), glutathione (GST), toll-like receptor (TLR), and lysozyme (LYZ) genes. Overall, 1 % supplementation significantly enhanced growth, antioxidant capacity, digestive ability, microbiota stability, and immune-related gene expression in S. intermedius.

Multiple effects of dietary supplementation with Lactobacillus reuteri and Bacillus subtilis on the growth, immunity, and metabolism of largemouth bass (Micropterus salmoides)

Probiotics play an essential role in the largemouth bass (Micropterus salmoides) aquaculture sector. They aid the fish in sickness prevention, intestinal structure improvement, food absorption, and immune system strengthening. In this experiment, Bacillus subtilis (BS, 107 CFU/g) and Lactobacillus reuteri (LR, 107 CFU/g) were added to the feed and then fed to M. salmoides for 35 days. The effects of two probiotics on the growth, immunity, and metabolism of M. salmoides organisms were studied. The results revealed that the BS group significantly increased the growth rate and specific growth rate of M. salmoides, while both the BS and LR groups significantly increase the length of villi M. salmoides intestines. The BS group significantly increased the levels of AKP, T-AOC, and CAT in the blood of M. salmoides, as well as AKP levels in the intestine. Furthermore, the BS group significantly increased the expression of intestinal genes Nrf2, SOD1, GPX, and CAT, while significantly decreasing the expression of the keap1 gene. M. salmoides gut microbial analysis showed that the abundance of Planctomycetota was significantly different in both control and experimental groups. Analyzed at the genus level, the abundance of Citrobacter, Paracoccus, Luedemannella， Sphingomonas, Streptomyces and Xanthomonas in the both control and experimental groups were significantly different. The BS group's differentially expressed genes were predominantly enriched in oxidative phosphorylation pathways in the intestine, indicating that they had a good influence on intestinal metabolism and inflammation suppression. In contrast, differentially expressed genes in the LR group were primarily enriched in the insulin signaling and linoleic acid metabolism pathways, indicating improved intestine metabolic performance. In conclusion, B. subtilis and L. reuteri improve the growth and health of M. salmoides, indicating tremendous potential for enhancing intestinal metabolism and providing significant application value.

Effects of solid-state fermentation product of yeast supplementation on liver and intestinal health, and resistance of common carp (Cyprinus carpio) against spring viraemia carp virus

This study aimed to investigate the effects of solid-state fermentation products of yeast (SFPY) on liver and intestinal health and disease resistance of common carp (Cyprinus carpio). A total of 200 common carp with an initial average weight of 2.55 ± 0.004 g were divided into 5 groups (4 replications per group and 10 fish per replication), and were fed with one of five diets, including a control diet and 4 diets supplemented with 2‰ (Y2), 3‰ (Y3), 4‰ (Y4), or 5‰ (Y5) SFPY, respectively, for 8 weeks. Results indicated that, the addition of SFPY to the diet of common carp did not affect the growth performance or survival rate of fish (P = 0.253). Interestingly, with the addition of SFPY, the triacylglycerol (TAG) content of the liver presented a linear decreasing tendency (P = 0.004), with significantly decreased in Y4 and Y5 groups (P = 0.035) compared with control. Serum lipopolysaccharide (LPS) content and diamine oxidase (DAO) activity presented a negative linear relationship with the addition of SFPY (P = 0.015, P = 0.030), while serum lipopolysaccharide binding protein (LBP) content first decreased and then increased (P < 0.001). The total antioxidant capacity (T-AOC) in the intestine of fish increased continuously with increasing SFPY supplementation (P = 0.026), reaching the highest level in Y5 group. The villus height in all experimental groups were significantly higher than that in the control group (P < 0.001). Furthermore, compared to the control, adding 3‰ SFPY to the control diet of common carp significantly increased the relative abundance of Fusobacteria (P = 0.018) and decreased that of Proteobacteria (P = 0.039) at phylum level, and increased the relative abundance of Cetobacterium (P= 0.018) and decreased that of Shewanella (P = 0.013) at genus level. Compared with the control, the relative mRNA expression level of spring viraemia of carp virus N protein (SVCV -n) in the kidney was lower than that of the control group without significance and bottomed out in Y4 group (P = 0.138). In conclusion, dietary SFPY enhanced the SVCV resistance capacity of common carp by improving liver and intestinal health and modulating the gut microbiota. Thus, SFPY is a potential feed additive to be used in aquaculture to reduce the huge economic loss of common carp due to SVCV disease. Based on liver TAG content and intestinal villus height, the optimal addition level of SFPY was 3.02‰ and 2.72‰, respectively.

Dietary inclusion of Clostridium butyricum cultures alleviated impacts of high-carbohydrate diets in largemouth bass (Micropterus salmoides)

A 60-d feeding trial was conducted to explore the potential regulatory effects of dietary Clostridium butyricum cultures (CBC) supplementation in high-carbohydrate diet (HCD) on carbohydrate utilisation, antioxidant capacity and intestinal microbiota of largemouth bass. Triplicate groups of largemouth bass (average weight 35·03 ± 0·04 g), with a destiny of twenty-eight individuals per tank, were fed low-carbohydrate diet and HCD supplemented with different concentration of CBC (0 %, 0·25 %, 0·50 % and 1·00 %). The results showed that dietary CBC inclusion alleviated the hepatic glycogen accumulation induced by HCD intake. Additionally, the expression of hepatic ampkα1 and insulin signaling pathway-related genes (ira, irb, irs, p13kr1 and akt1) increased linearly with dietary CBC inclusion, which might be associated with the activation of glycolysis-related genes (gk, pfkl and pk). Meanwhile, the expression of intestinal SCFA transport-related genes (ffar3 and mct1) was significantly increased with dietary CBC inclusion. In addition, the hepatic antioxidant capacity was improved with dietary CBC supplementation, as evidenced by linear decrease in malondialdehyde concentration and expression of keap1, and linear increase in antioxidant enzyme activities (total antioxidative capacity, total superoxide dismutase and catalase) and expression of antioxidant enzyme-related genes (nrf2, sod1, sod2 and cat). The analysis of bacterial 16S rRNA V3-4 region indicated that dietary CBC inclusion significantly reduced the enrichment of Firmicutes and potential pathogenic bacteria genus Mycoplasma but significantly elevated the relative abundance of Fusobacteria and Cetobacterium. In summary, dietary CBC inclusion improved carbohydrate utilization, antioxidant capacity and intestinal microbiota of largemouth bass fed HCD.

The preferential utilization of hepatic glycogen as energy substrates in largemouth bass (Micropterus salmoides) under short-term starvation

To elucidate the underlying mechanism of the energy metabolism in largemouth bass (Micropterus salmoides), cultured fish (initial body weight: 77.57 ± 0.75 g) in the present study were starved for 0 h, 12 h, 24 h, 48 h, 96 h and 192 h, respectively. The proximate composition analysis showed that short-term starvation induced a significant up-regulation in crude protein proportion in hepatic of cultured fish (P < 0.05). However, short-term starvation significantly decreased the hepatosomatic index and the viscerosomatic index of cultured fish (P < 0.05). The exact hepatic glycogen content in the group starved for 92 h presented remarkable decrease (P < 0.05). Meanwhile, compared with the weight change of lipid and protein (mg) in hepatic (y = 0.0007x2 - 0.2827x + 49.402; y = 0.0013x2 - 0.5666x + 165.31), the decreasing trend of weight in glycogen (mg) was more pronounced (y = 0.0032x2 - 1.817x + 326.52), which suggested the preferential utilization of hepatic glycogen as energy substrates under short-term starvation. Gene expression analysis revealed that the starvation down-regulated the expression of insulin-like growth factor 1 and genes of TOR pathway, such as target of rapamycin (tor) and ribosomal protein S6 (s6) (P < 0.05). In addition, the starvation significantly enhanced expression of lipolysis-related genes, including hormone-sensitive lipase (hsl) and carnitine palmitoyl transferase I (cpt1), but down-regulated lipogenesis as indicated by the inhibited expression of fatty acids synthase (fas), acetyl-CoA carboxylase 1 (acc1) and acetyl-CoA carboxylase 2 (acc2) (P < 0.05). Starvation of 24 h up-regulated the expression of glycolysis genes, glucokinase (gk), phosphofructokinase liver type (pfkl) and pyruvate kinase (pk), and then their expression returned to the normal level. Meanwhile, the expression of gluconeogenesis genes, such as glucose-6-phosphatase catalytic subunit (g6pc), fructose-1,6-bisphosphatase-1 (fbp1) and phosphoenolpyruvate carboxy kinase (pepck), was significantly inhibited with the short-term starvation (P < 0.05). In conclusion, short-term starvation induced an overall decline in growth performance, but it could deplete the hepatic glycogen accumulation and mobilize glycogen for energy effectively.

Effects of sodium butyrate on growth performance, antioxidant status, inflammatory response and resistance to hypoxic stress in juvenile largemouth bass (Micropterus salmoides)

The aim of this study was to investigate the effects of sodium butyrate (SB) supplementation on growth performance, antioxidant enzyme activities, inflammatory factors, and hypoxic stress in largemouth bass (Micropterus salmoides). Diets were supplemented with different doses of SB at 0 (SB0), 0.5 (SB1), 1.0 (SB2) and 2.0 (SB3) g/kg. The hypoxic stress experiment was performed after 56 days of culture. The results showed that compared with the SB0 group, the final body weight, weight gain rate and protein deposition rate of the SB3 group were significantly increased (P<0.05), while FCR was significantly decreased (P<0.05). The contents of dry matter, crude lipids, and ash in the SB2 group were significantly higher than those in the SB0 group (P<0.05). The urea level was significantly decreased (P<0.05), and the glucose content was significantly increased (P<0.05) in the SB supplement group. Compared with the SB0 group, the SB2 group had significant reductions in the levels of serum triglyceride, cholesterol, elevated-density lipoprotein cholesterol, and low-density lipoprotein (P<0.05), and significant reductions in the levels of liver alkaline phosphatase and malondialdehyde (P<0.05). The total antioxidant capacity of the SB1 group was higher than that of other groups (P<0.05). Compared with the SB0 group, the mRNA expression of TLR22, MyD88, TGF-β1, IL-1β and IL-8 in the SB2 group significantly decreased (P<0.05). The cumulative mortality rate was significantly decreased in the SB2 and SB3 groups in comparison with that in the SB0 group after three hours of hypoxic stress (P<0.05). In a 56-day feeding trial, SB enhanced largemouth bass growth by increasing antioxidant enzyme activity and inhibiting TLR22-MyD88 signaling, therefore increasing cumulative mortality from hypoxic stress in largemouth bass.

Live Yeast (Saccharomyces cerevisiae var. boulardii) Supplementation in a European Sea Bass (Dicentrarchus labrax) Diet: Effects on the Growth and Immune Response Parameters

The present study has been aimed at evaluating the effects of the dietary inclusion of the live yeasts, Saccharomyces cerevisiae var. boulardii (LSB) administered at increasing concentrations (0, 100, and 300 mg kg-1 of feed, here referred to as LSB 0, 100, 300) for 90 days, on the health conditions of European sea bass. The main zootechnical parameters, histological and morphological analyses, innate immunity response parameters (intestinal cytokine expression, lysozyme content, spontaneous hemolytic and hemagglutinating activities, antibacterial activities, and peroxidase activity) were measured as fish welfare parameters. LSB did not impair either growth parameters or the morphometric indexes. LSB down-regulated interleukin-1β transcription in the distal gut of fish treated with 5.4 × 105 CFU g-1 (LSB100) for 21 days. The interleukin-6 mRNA level decreased significantly in the proximal gut for both doses of yeast, after 21 days of feeding; the gene expression of interleukin-6 was significantly lower in the sea bass fed 10.81 × 105 CFU g-1 (LSB300) probiotic. The levels of TNF-α mRNA were not influenced by probiotic supplementation. Increases, although not significant, in the hematological and immunological parameters were also recorded. The data collected in the present study suggests that an LSB-supplemented diet acts on the gut immune system of sea bass by modulating the expression of the key inflammatory genes.

The Combined Supplementation of AZOMITE and Citric Acid Promoted the Growth, Intestinal Health, Antioxidant, and Resistance against Aeromonas hydrophila for Largemouth Bass, Micropterus salmoides

Citric acid is an organic acid extensively used in feed industry, and AZOMITE is a hydrated aluminosilicate compound rich in rare earth elements and trace mineral elements. This study investigated the supplemental effects of AZOMITE and citric acid individual or in combination on the growth performance, intestinal microbiota, morphology, digestive enzyme activity, serum indexes, and disease resistance of juvenile largemouth bass. Six diets were designed, including the control diet (CON) and the five additive-supplemented diets with the addition of 4 or 8 g/kg citric acid (CA4, CA8), 3 g/kg AZOMITE (A3), and their combined addition as 4 g/kg citric acid + 1.5 g/kg AZOMITE) (C4A1.5) and 8 g/kg citric acid + 3 g/kg AZOMITE (C8A3). Juvenile largemouth bass with initial body weight of 22.01 ± 0.09 g were fed the six diets for 56 days. The results revealed that the combined addition of 4 g/kg citric acid and 1.5 g/kg AZOMITE (C4A1.5) increased weight gain by 7.99% (P < 0.05), and decreased feed conversion ratio by 0.07 (P < 0.05). The protein retention in the C4A1.5 group and the lipid retention in all additive-supplemented groups were significantly higher than those in the control group (P < 0.05). In serum, all additive-supplemented groups showed significantly higher glutathione peroxidase activity than the control group (P < 0.05). The activities of superoxide dismutase and catalase in the CA8, A3, C4A1.5, and C8A3 groups were significantly higher (P < 0.05), while the concentration of malondialdehyde was significantly lower than those in the control group (P < 0.05). Moreover, the total antioxidant capacity in the A3 and C4A1.5 groups, and lysozyme activity in the A3, C4A1.5, and C8A3 groups were significantly increased when compared to the control group (P < 0.05). In digestive enzyme, the protease activity in the A3, C4A1.5 groups, and amylase activity in the CA4, CA8, and C4A1.5 groups were significantly higher than those in the control group (P < 0.05). In intestinal microbiota, Firmicutes abundance was elevated in all additive groups, while the Fusobacteriota and Plesiomonas shigelloides abundance were decreased. In the intestinal histology, the CA8, A3, and C4A1.5 groups showed significantly higher villus height than the control group (P < 0.05). After the infection with Aeromonas hydrophila, the cumulative mortality of all additive-supplemented groups was significantly lower (P < 0.05), and the C4A1.5 group demonstrated the lowest mortality. In conclusion, the combined supplementation of 4 g/kg citric acid + 1.5 g/kg AZOMITE increased the growth, antioxidant, immune capacity, improved the intestinal morphology and microbial flora of juvenile largemouth bass, and promoted the resistance against Aeromonas hydrophila infection.

Effects of Three Feed Additives on the Culturable Microbiota Composition and Histology of the Anterior and Posterior Intestines of Zebrafish (Danio rerio)

In this study, the effect of three promising feed additives (chelated compounds of trace elements, butyric acid, lycopene) on changes in the culturable microbiota and histological parameters of two sections of the intestines of Danio rerio (zebrafish) was studied. The use of these feed additives can help to eliminate the deficiency of trace elements, modulate the composition of the microbiota due to the postbiotic properties of butyric acid, and reduce oxidative stress when using lycopene. Incorporation of the investigated supplements in the feed resulted in a significant change in the relative abundance of certain groups of microorganisms. The taxonomic diversity of cultured microorganisms did not differ in the anterior and posterior intestines, while there were differences in the relative abundance of these microorganisms. The most sensitive groups of microorganisms were the genera Bacillus and Serratia. A significant effect on the composition of the cultured microbiota was caused by lycopene (in all studied concentrations), leading to a significant increase in the relative abundance of Firmicutes in the anterior gut. Studies of the histological structure of the anterior and posterior guts have shown the relationship between the barrier and secretory functions of the gut and the composition of the microbiota while using butyric acid (1 and 2 g kg-1) and trace element chelated compounds (2 mg kg-1). This culture-dependent method of studying the microbiome makes it possible to assess changes in some representatives of the main groups of microorganisms (Firmicutes and Proteobacteria). Despite the incompleteness of the data obtained by the culture-dependent method, its application makes it possible to assess the bioactive properties of feed and feed additives and their impact on the microbiota involved in digestive processes.