Pengwei Xun

Essential oils serve as potential additives that can enhance immune respons and disease resistance and regulate the gut microbiota of fish. Here, this research aims to identify the impacts of eucalyptus essential oil (EEO) on growth, liver antioxidative and immune parameters, resistance to Streptococcus iniae, intestinal morphology and gut microbiota in Trachinotus ovatus. All fish (initial weight: 26.87 ± 0.30 g) were randomly allocated to 12 floating cages (2.0 × 2.0 × 2.0 m³) with each cage containing 100 fish and fed for 30 days. Four diets were manufactured with the supplementation of varying levels of EEO (control and 5.0, 10.0, and 15.0 mL/kg) and were named CG, EEO1, EEO2 and EEO3, respectively. The results showed that EEO1 and EEO2 diets significantly increased WGR, thickness of the intestinal muscle layer, and the ratio of villus height to crypt depth (V/C), while decreasing the intestinal crypt depth of T. ovatus (p < 0.05). Significantly increased activities of SOD and CAT and significantly reduced MDA levels were present in the EEO1 and/or EEO2 groups (p < 0.05). Moreover, the mRNA levels of nrf2, HO-1, GSH-Px, SOD, C4 and GR genes were significantly upregulated and the expression of keap1 and HSP70 genes were significantly downregulated within the EEO1 and EEO2 groups (p < 0.05). After challenge with S. iniae B240703 for 24 h, the bacterial load for five organs in the EEO2 group was less than that in the CG group (p < 0.05). In addition, the fish fed EEO1 and/or EEO2 diets had significantly lower abundances of pathogenic bacteria (Proteobacteria, Planctomycetota, Burkholderia-Caballeronia-Paraburkholderia, Pseudomonas and Blastopirellula) and a higher beneficial bacteria proportion (Firmicutes) than those fed the CG diets (p < 0.05). In conclusion, a moderate dietary m EO level (5.0~10.0 mL/kg) improved the growth and gut morphology, promoted liver immune response, enhanced resistance to S. iniae and modulated the gut microbiota of T. ovatus.

This study aims to investigate the effects of potassium diformate (KDF) and sodium propionate (NaP) on gut digestive and immune functions, intestinal microbiota, and lipid metabolites of Trachinotus ovatus based on multiomics approach. Juvenile T. ovatus (initial weight: 8.65 ± 0.02 g) were subjected to a 56‐day feeding regimen. Three isonitrogenous and isolipidic diets, including the control (CG), an additional 6.6 g/kg of KDF, and an additional 6.0 g/kg of NaP were fed to juvenile fish twice daily. Results showed that KDF and NaP supplementation significantly increased the activities of chymotrypsin (Chy), lipase (Lip), α‐amylase (α‐amy), creatine kinase (CK), Na ⁺ K ⁺ ‐ATPase (Na ⁺ K ⁺ ‐ATP), γ‐glutamyl transferase (γ‐GT), alkaline phosphatase (AKP), glutathione peroxidase (GSH‐Px), total antioxidant capacity (T‐AOC), and superoxide dismutase (SOD) as well as the expression level of Nrf2 ( p < 0.05), while decreased the pH value, malondialdehyde (MDA) content and the mRNA level of Keap1 ( p < 0.05). Dietary KDF and NaP markedly enhanced microbial α‐diversity and induced significant shifts in microbiota composition through selective modulation of bacterial populations, such as Photobacterium , Mycoplasma , and Mycobacterium ( p < 0.05). Besides, KDF and NaP led to notable alterations in the intestinal metabolite lipidome through increasing short‐chain fatty acids (SCFAs) levels, upregulating the abundance of phosphatidylcholine (PC), phosphatidylethanolamine, methyl PC (MePC), lysophosphatidic acid, ceramide (Cer), sitosteryl, monogalactosyldiacylglycerol, coenzyme, and lysophosphatidylethanolamine and downregulating the abundance of sphingomyelin and monoglyceride ( p < 0.05). The assessment of associations revealed inverse relationships of digestive and antioxidative indices with Photobacterium , but positive correlations with Mycoplasma , Mycobacterium , Ruegeria , Synechococcus , Nautella , Turicibacter , and Roseovarius . This study advances our understanding of KDF and NaP on intestinal health.

Seven graded levels of sodium propionate (SP) diets with 0 (SP1), 0.2% (SP2), 0.4% (SP3), 0.6% (SP4), 0.8% (SP5), 1.0% (SP6), and 1.2% (SP7) were prepared to feed Trachinotus ovatus (initial body weight: 8.64 ± 0.08 g) for 56 days. The results showed that increasing dietary SP levels quadratically increased significantly final body weight (FBW), weight gain rate (WGR), and specific growth rate (SGR) of T. ovatus but linearly and quadratically decreased significantly viscerosomatic index (VSI) and hepatosomatic index (HSI) of T. ovatus (P < 0.05). In the SP4 treatment, FBW, WGR, and SGR presented the highest values. Both positive linear and quadratic trends were detected between crude lipid content of whole fish, adhesiveness of dorsal muscle, white blood cell (WBC), red blood cell (RBC), hemoglobin (HGB), blood performance, high‐density lipoprotein cholesterol (HDL‐c), intestinal villus height, and dietary SP level, while negative linear and quadratic trends were found between firmness of dorsal muscle, triglyceride (TG), glucose (GLU), and dietary SP level (P < 0.05). The increasing SP led to quadratic increases in lymphocyte (Lym), complement 3 (C3), chymotrypsin, villus number, and muscle layer thickness, and a quadratic decrease in hepatic malondialdehyde (MDAP < 0.05). A significant negative linear trend was found between the content of glutamic‐pyruvic transaminase (GPT) and dietary SP level, while significant positive linear trends were presented between C4, immunoglobulin M (IgM), α‐amylase and dietary SP level (P < 0.05). The increasing SP resulted in linear and quadratic increases in superoxide dismutase (SOD), total antioxidant capacity (T‐AOC) of livers and C3, C4, IgM of head kidney (P < 0.05). The expression levels of tumor necrosis factor alpha (TNF-α) and interleukin‐8 (IL-8) were linearly and quadratically decreased, while the mRNA levels of growth factor beta (TGF-β) were linearly and quadratically increased with the increasing SP level (P < 0.05). In conclusion, SP could be considered as a beneficial feed additive for enhancing growth and immunity of fish. And dietary SP level at 0.6% is optimal for the growth of Trachinotus ovatus based on a quadratic regression model of WGR.

Experimental diets were formulated including the suitable lipid level (10%, PC), the high‐lipid level (16%, HL), and HL containing sodium acetate diets (HS). Three diets were fed golden pompano (Trachinotus ovatus) (initial body weight: 12.88 ± 0.03 g) for 8 weeks. The results showed HL diets significantly increased hepatosomatic index (HSI) and abdominal fat percentage (ASF), aggravated liver lipid deposition, and caused blood metabolic disorder and liver damage (P < 0.05). Moreover, the fish fed HL diets significantly decreased intestinal villus number (VN) and muscular layer thickness (MLT) (P < 0.05), accompanied with an increased trend in the relative abundance of intestinal pathogenic bacteria such as Mycoplasma and Photobacterium. However, the fish fed HS diets significantly decreased the HSI and AFP, relieved hepatic lipid deposition, improved blood and liver metabolism, and intestinal morphology in comparison to the fish fed HL diets (P < 0.05). More importantly, sodium acetate addition improved intestinal microbiota by inhibiting the proportion of pathogens (Mycoplasma and Vibrio) and increasing the abundance of probiotics (Bacteroidales_S24-7_group_norank, Cetobacterium, Bacteroides, and Lachnospiraceae_NK4A136_group). Furthermore, there was a strong correlation between these bacteria (Mycoplasma, Vibrio, Lachnospiraceae_NK4A136_group, Bacteroidales_S24-7_group_norank, Bacteroides, and Cetobacterium) and main physiological indices. In conclusion, sodium acetate improved blood performance, alleviated hepatic lipid deposition induced by HL diets, and boosted the growth and intestinal health for golden pompano.

Six isonitrongenous and isolipidic diets were formulated to feed 360 fish (mean initial body weight: g) with graded levels of sodium acetate (SA1 (0), SA2 (250 mg/kg), SA3 (500 mg/kg), SA4 (1000 mg/kg), SA5 (2000 mg/kg), and SA6 (4000 mg/kg)) for 8 weeks. The results revealed that weight gain rate, specific growth rate, and feed intake of golden pompano were significantly increased in SA3 and SA4 treatments ( ). Dietary SA level significantly improved lipid contents and gumminess of muscle ( ). Supplement levels of dietary SA significantly influenced plasma biochemical parameters containing triglyceride, glucose, high-density lipoprotein cholesterol, complements, and immunoglobulin M ( ). Appropriate supplement levels of dietary SA significantly increased enzyme activities of hepatic superoxide dismutase and total antioxidant capacity and decreased malondialdehyde contents ( ). Furthermore, appropriate SA levels downregulated the expression levels of Keap1, IL-8, TNF-α, and NF-κB genes and upregulated the expression levels of Nrf2 and TGF-β genes of the spleen ( ). Excess SA caused negative effects for Trachinotus ovatus. The optimum supplement level of SA for juvenile golden pompano was evaluated to be 1423.67 mg/kg based on WGR.