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Clostridium butyricum (CB) is known to promote growth, enhance immunity, promote digestion, and improve intestinal health. In this study, we investigated the effects of CB in the feed on growth performance, digestion, and intestinal health of juvenile spotted sea bass. To provide a theoretical basis for the development and application of CB in the feed of spotted sea bass, a total of 450 spotted sea bass with an initial body weight of (9.58 ± 0.05) g were randomly divided into six groups. Gradient levels with 0, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% of CB (1×10 9 cfu/g) were supplemented into diets, designated as CC, CB1, CB2, CB3, CB4, and CB5, respectively. Each group was fed for 54 days. Our results suggest that dietary 0.2% and 0.3% of CB can significantly increase the weight gain (WG) and specific growth rate (SGR) of spotted sea bass. The addition of CB significantly increased intestinal amylase activity, intestinal villus length, intestinal villus width, and intestinal muscle thickness. Similarly, CB supplementation increased the expression of tumor necrosis factor- α ( TNF-α ) and interleukin-8 ( IL-8 ). Sequence analysis of the bacterial 16S rDNA region showed that dietary CB altered the intestinal microbiota profile of juvenile spotted sea bass, increasing the dominant bacteria in the intestine and decreasing the harmful bacteria. Overall, dietary addition of CB can improve growth performance, enhance intestinal immunity, improve intestinal flora structure, and comprehensively improve the health of spotted sea bass.

High soybean meal diet (HSBMD) decreased the immunity and damaged the liver health of spotted sea bass; in this study, Lycium barbarum polysaccharides (LBP) was added to HSBMD to explore its effects on the immunity and liver health. The diet with 44% fish meal content was designed as a blank control. On this basis, soybean meal was used to replace 50% fish meal as HSBMD, and LBP was added in HSBMD in gradient (1.0, 1.5, 2.0 g/kg) as the experimental diet. 225-tailed spotted sea bass with initial body weight of 44.52 ± 0.24 g were randomly divided into 5 groups and fed the corresponding diet for 52 days, respectively. The results show that: after ingestion of HSBMD, the immunity of spotted sea bass decreased slightly and hepatic tissue was severely damaged. And the addition of LBP significantly improved the immune capacity and protected the hepatic health. Specifically, the activities of serum lysozyme (LZM), immunoglobulin M (IgM), liver acid phosphatase (ACP) and alkaline phosphatase (AKP) were increased, and serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities were significantly decreased, and hepatic morphology was improved. In the analysis of transcriptome results, it was found that toll-like receptor 3 (TLR3) and toll-like receptor 5 (TLR5) were down-regulated in toll-like receptor signaling pathway. And LBP may protect hepatic health by regulating Glycolysis/Gluconeogenesis, Insulin signaling pathway, Steroid biosynthesis and other glucolipid-related pathways. In conclusion, the addition of LBP in HSBMD can improve the immunity and protect the hepatic health of spotted sea bass, and its mechanism may be related to glucose and lipid metabolism.

Temperature affects the metabolism of fish, and fish of different sizes have different tolerances to temperature. The aim of this experiment was to compare two sizes of juvenile spotted seabass, Lateolabrax maculatus (with average weights of 57.91 ± 11.57 g and 13.92 ± 2.77 g, respectively) for changes in physiological, biochemical, and molecular mechanisms under acute heat stress. Experimental fish were exposed to acute temperature increasing from 23 °C to 32 °C, and the mortality rate was noted at various heat stress exposures (0, 3, 6, 12, 24, 48, and 72 h). Moreover, serum and liver were obtained before and after heat stress. The activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT), superoxide dismutase (SOD), malondialdehyde (MDA), lactic acid (LD), lactate dehydrogenase (LDH), glucose, and hepatic glycogen, and the expression of heat shock proteins (HSP70, HSP90) and apoptosis-related genes (BAX, caspase-3) in two sizes of spotted seabass were measured. Results showed that the contents of AST, ALT, SOD, MDA, LD, and glucose as well as the expression level of BAX and mortality were higher in large spotted seabass than in small spotted seabass within 12 h. These results indicate that the large spotted seabass had higher levels of oxidative stress and more severe liver damage, resulting in a higher mortality. Furthermore, the HSPs expression level of small spotted seabass was higher and the mortality was lower than that of large spotted seabass. Therefore, we considered that the large spotted seabass has lower levels of HSPs expression, causing their physiological response to be elevated to resist heat stress. In conclusion, spotted seabass with larger size has a poorer tolerance to heat stress compared with spotted seabass with smaller size. The smaller fish size was possibly resistant to heat stress by regulating the HSPs expression level in a more active extent.

The study investigated the impact of chlorogenic acid (CGA) supplementation in a high-fat diet (HFD) on growth, lipid metabolism, intestinal and hepatic histology, as well as gut microbiota in spotted sea bass. A total of 540 fish were fed six experimental diets, including a normal fat diet (NFD), a high-fat diet (HFD), and HFD supplemented with 100, 200, 300, and 400 mg/kg CGA (named HFD1, HFD2, HFD3, and HFD4, respectively) for 7 weeks. The results showed that HFD feeding increased growth and hepatic lipid deposition compared to that in the NFD group. Inclusion of 300 mg/kg CGA in HFD decreased the HFD-induced hyperlipemia (p < 0.05). Additionally, compared to the HFD group, the HFD4 group showed significant reductions in serum aspartate transaminase (AST) and alanine transaminase (ALT) levels as well as hepatic malondialdehyde (MDA) content, while also improving liver total antioxidant capacity (T-AOC) (p < 0.05). In the CGA-containing groups, hepatocytes were arranged more neatly than those in the HFD group, and there was a reduction in lipid deposition and hemolysis in the liver. Supplementation of CGA had effects on intestinal structure including an increase in mucosal thickness, as well as villus number and width. The diversity of intestinal flora in the CGA-containing groups was higher than those in the HFD group, and supplementation of 200 mg/kg CGA significantly increased the abundance of intestinal bacteria (p < 0.05). HFD4 feeding increased the intestinal Bacteroidetes to Firmicutes ratio and decreased the abundance of Vibrio. The highest value abundance of Actinobacteriota was found in the HFD2 group. Overall, HFD caused negative effects, and supplementation of 200–400 mg/kg CGA to HFD improved fat deposition, lipid metabolic disorders and liver and gut histology, and increased gut bacterial diversity in spotted sea bass.

Laminarin has antioxidant and immunomodulatory properties and favorably impacts gut microbial composition, providing a potential solution for the treatment of intestinal diseases in fish. The aim of this study was to investigate the effects of laminarin on the growth and intestinal health of juvenile spotted seabass, Lateolabrax maculatus . A total of 450 juveniles (initial body weight: 7.14 ± 0.10 g) were randomly divided into 6 groups with 3 replicates per group and 25 fish per replicate. Six diets were prepared with laminarin supplementation at doses of 0% (Control), 0.4% (P0.4), 0.8% (P0.8), 1.2% (P1.2), 1.6% (P1.6), and 2% (P2). Each group was fed the corresponding diet for 8 weeks. The results indicated that dietary laminarin supplementation of 0.4-1.6% enhanced the specific growth rate (SGR), weight gain rate (WGR), and feed conversion ratio (FCR) of juvenile spotted seabass, and the difference was significant in the P0.8 group ( P <0.05). Significantly higher intestinal amylase activity was measured in P0.8 compared with the control group. Trypsin activity was significantly increased in P0.4 and P0.8 groups in contrast to the control ( P <0.05). Lipase activity was significantly increased in P0.4, P0.8, P1.6, and P2 groups in contrast to the control ( P <0.05). Total antioxidant capacity was significantly increased in the P0.8, P1.2, and P1.6 groups compared to the control group ( P <0.05). The P0.8 group exhibited significant increases in reduced glutathione, alkaline phosphatase, and lysozyme levels ( P <0.05), whereas the concentrations of diamine oxidase and D-lactate were significantly decreased ( P <0.05). Furthermore, intestinal villus height, villus width, and crypt depth were significantly increased in P0.8 and P2 groups ( P <0.05), and muscular thickness was significantly increased in the P1.2 group ( P <0.05). Intestinal microbial analysis revealed that the alpha diversity of the laminarin supplemented groups was significantly higher than that of the control group. Moreover, the abundance of intestinal beneficial bacteria Lactobacillus and Klebsiella in P0.4 and P0.8 groups was significantly increased ( P <0.05), indicating that laminarin altered the composition of intestinal flora and the abundance of dominant bacteria, with a low dose being more conducive to the formation of beneficial bacteria. In conclusion, dietary laminarin supplementation can improve the growth performance and intestinal function of juvenile spotted seabass. Based on the regression analyses of weight gain rate and specific growth rate, the optimal supplemental level of laminarin was estimated to be 0.97% and 0.98%, respectively.

Mulberry leaf extract (ELM) has the functions of promoting growth, antioxidant, improving intestinal microbial composition, thus providing a potential solution the occurrence of fish intestinal diseases. Therefore, this experiment was conducted to explore the effects of ELM on intestinal health of spotted sea bass Lateolabrax maculatus . A total of 360 spotted sea bass (9.00 ± 0.02 g) were selected and randomly divided into 6 groups. Fish in each group were given feed with varying ELM concentration (0, 3, 6, 9, 12, 15 g/kg) for 52 days, respectively. Results show, dietary intake of 9 g/kg ELM increased the weight gain, specific growth ratio and feed intake of the spotted sea bass ( P <0.05). Meanwhile, dietary intake of 9 g/kg ELM increased the activity of enteric trypsin, amylase and lipase ( P <0.05). The enteric catalase activity was improved in fish fed with 3 g/kg ELM ( P <0.05), while a limited effect of ELM on the activity of enteric superoxide dismutase, glutathione, and content of malonaldehyde was observed ( P >0.05). ELM improved the morphology of fish intestine, as manifested in significant improvement in the length of intestinal villi, thereby increasing the surface area of the intestinal tract ( P <0.05). Compared with the control group, dietary intake of ELM significantly increased the intestinal microbial ACE, Chao1, and Shannon indexes of fish ( P <0.05), indicated that the intestinal microbial composition and the abundance of the dominant flora of fish were improved. The above results suggested that the dietary supplementation of about 9 g/kg ELM can improve the growth performance, enteric antioxidant capacity, and intestinal morphology and microbial composition, therefore improving the intestinal health of spotted sea bass. The research results provide a theoretical basis for the application of ELM in improving the enteric health of spotted sea bass, and providing a potential solution the occurrence of fish intestinal diseases.

Porphyra yezoensis polysaccharides (PPs) have biological activities such as promoting digestion, functioning as antioxidants, and improving intestinal health. The aim of this study was to investigate the effects of PPs on the intestinal health of spotted sea bass (Lateolabrax maculatus). A total of 360 spotted sea bass (10.53 ± 0.02 g) were randomly divided into six groups. Fish in each group were fed with varying PP concentrations (0, 3, 6, 9, 12, 15 g/kg) for 52 days. The results showed that 12 g/kg PPs significantly increased the body weight gain, specific growth rate, and condition factor, while there was no significant change in the feed conversion ratio. A supplementation dosage of 9 g/kg PPs significantly increased intestinal amylase activity, and 12 g/kg PPs supplementation significantly increased intestinal trypsin activity. In addition, compared with the control group, there was no difference in lipase in the experimental groups. When fed 9 g/kg, the intestinal glutathione content was significantly increased, and the malondialdehyde content was significantly decreased; the effect of PPs on the catalase activity was not significant. PPs improved intestinal morphology, specifically by improving the intestinal villus morphology and increasing the intestinal lining surface area. Compared with the control group, PPs increased the abundance of Firmicutes and Bacteroides. At the genus level, Cyanobacteria, Muribaculaceae, and Lachnospiraceae were the main flora in the intestinal tract of spotted sea bass. In addition, PPs increased ACE and Chao1 indices of the intestinal microorganisms, while the Simpson index and Shannon index did not change significantly, indicating that intestinal microbial composition and abundance had increased to a certain extent. The results indicated that different levels of PPs in feed can improve the intestinal physiological and biochemical indexes, intestinal morphology, and microbial composition, and thus improve the intestinal health of spotted sea bass.

This study explored the effects of chlorogenic acid (CGA) on antioxidant capacity, immunity, and intestinal health of spotted sea bass Lateolabrax maculatus . Spotted sea bass were fed six diets: a normal-fat diet (NFD) with 11.9% lipid; HFD with 17% lipid (HFD); and HFD supplemented with 100, 200, 300, and 400 mg/kg CGA (HFD1, HFD2, HFD3, and HFD4 respectively) for 7 weeks. Results showed that HFD-feeding significantly decreased CAT and T-SOD activity compared to the containing-CGA groups. Dietary supplementation with 300 mg/kg CGA significantly reduced MDA content and increased T-AOC compared to the HFD group. HFD supplemented with 100 and 200 mg/kg CGA significantly enhanced GSH activity compared to the HFD group. The activity of ACP and AKP significantly increased with 200 mg/kg CGA treatment compared to the HFD group. Compared to the HFD group, dietary CGA significantly increased the levels of LZM. CGA supplementation at 100, 200, and 300 mg/kg CGA significantly increased the levels of complement C3 compared to that in the HFD group. Supplementation of 300 and 400 mg/kg CGA significantly improved the lipase activity in the foregut compared with the HFD group. For histological analysis, HFD-feeding led to a reduction in muscular thickness, villi length, and density of the midgut compared to the NFD group, while the addition of CGA can improve the negative effects induced by HFD. Additionally, HFD-feeding increased both the diversity and abundance of intestinal bacteria in the midgut compared to the NFD diet, while contrasting results were observed in the hindgut. Furthermore, the addition of CGA mitigated the reduction in hindgut bacterial diversity induced by HFD. Overall, the present study indicated that dietary CGA plays a positive role in antioxidant capacity, immunity, and intestinal health of fed HFD.

Clostridium butyricum (CB) has received much attention as a probiotic; however, few studies have focused on its effects on liver health. Here, we studied the influence of CB on the liver health of spotted sea bass through transcriptomics and metabolomics studies and preliminarily explored its molecular mechanisms. This study showed that CB significantly reduced hepatic aspartate aminotransferase (AST) activity and increased alkaline phosphatase (AKP) and acid phosphatase (ACP) activity ( P < 0.05). CB has demonstrated significant effects in strengthening liver immunity and can increase hepatic amylase and trypsin activities and promote hepatic catabolism of carbohydrates and amino acids. Integration of the liver transcriptomics and metabolomics showed altered transcript levels of mainly gluconeogenic, lipogenic, and amino acid metabolic pathways. It regulated the abundance of metabolic biomarkers such as arachidonate, crotonyl-CoA, and D-glucose 1-phosphate. Our findings support that CB can reduce liver damage in spotted sea bass, enhance liver immunity, and improve liver metabolism.

This study investigated the effects of Porphyra yezoensis polysaccharide (PP) on the antioxidant and liver health of spotted sea bass ( Lateolabrax maculatus ). A total of 360 spotted sea bass (10.53 ± 0.02 g) were divided into 6 groups on average, and the diets of these groups were supplemented with 0, 3, 6, 9, 12, and 15 g/kg PP (control group: K, PP1, PP2, PP3, PP4, and PP5), respectively. The experiment lasted for 52 days. The results showed that, compared with the control group, the serum glutathione (GSH) content was significantly increased and the malondialdehyde (MDA) content was significantly decreased in the PP1 group. The serum catalase (CAT) activity was significantly increased in the PP1, PP2, PP3, and PP4 groups. Additionally, the superoxide dismutase (SOD) activity was significantly increased in the PP2 and PP3 groups. In terms of liver antioxidant indexes, GSH and MDA content were not significantly different among all groups. CAT activity in the PP2 and PP3 groups was significantly higher than that in the control group, and SOD activity in the PP4 groups was significantly higher than that in the control group. The activity of amylase (AMS) and trypsin (TRS) was significantly increased in the PP1, PP2, PP3, and PP4 groups compared to the control group. Additionally, the activity of lipase (LPS) was significantly increased in the PP5 group compared to the control group. Liver injury indexes showed that serum GOT and GPT activities in the PP3 group were significantly lower than those in the control group. There was no significant difference in T-CHO and TG between the experimental group and the control group. Histological analysis showed that dietary PP improved liver cell morphology and reduced fat vacuoles. Liver transcriptome analysis of the control group and the PP4 group showed that the main change pathways were arachidonic acid metabolism, purine metabolism, and fatty acid degradation. In addition, PP regulates fibroblast growth factor 19 (FGF19), solute carrier family 3,expression of member 2 (SLC3A2), angiopoietin-like 8 (ANGPTL8), thrombospondin 1 (THBS1), tyrosinase (TYR), and kelch-like protein 19 (KEAP1) genes, making adjustments to liver health and function. In summary, PP increased the antioxidant capacity and improved the liver health of spotted sea bass.