Background/Objectives: Carvacrol, a major active component of oregano oil and common feed additive, has been widely studied for its effects on fish growth, immunity, and intestinal health. But its transcriptional/metabolic impacts on fish liver remain unclear. This study investigated these effects in Pengze crucian carp (Carassius auratus var. Pengze). Methods: Fish were fed a basal diet (control) or basal diet supplemented with 10% microencapsulated carvacrol (600 mg/kg) for 56 days; liver samples were analyzed via transcriptomics and metabolomics. Results: Transcriptomic analysis revealed 482 differentially expressed genes (DEGs) in the liver of Pengze crucian carp following carvacrol supplementation, with 158 upregulated and 324 downregulated genes. Functional annotation highlighted enrichment in translation, signal transduction, amino acid metabolism, and posttranslational modification pathways. GO analysis further identified key processes, including carboxylic acid transport, tRNA aminoacylation, and mitochondrial nucleoid function, while KEGG pathways were implicated in amino acid biosynthesis, lipid metabolism (e.g., alpha-linolenic acid), and insulin signaling. Metabolomic profiling identified 679 significantly altered metabolites, including 113 upregulated and 566 downregulated ones. Among these, upregulated compounds like L-asparaginyl-L-lysine (Log₂FC = 4.36) and 2′-Deoxyadenosine-5′-diphosphate (Log₂FC = 4.31) are linked to nucleotide metabolism, and downregulated peptides (e.g., Ala-Phe-Tyr-Arg) suggesting modulated protein turnover. Joint omics analysis revealed convergent pathways in glycerophospholipid metabolism, aminoacyl-tRNA biosynthesis, and autophagy. Notably, the chaperone gene dnaja3b was correlated strongly with neuroactive metabolites (e.g., normetanephrine), potentially implicating carvacrol in stress response regulation. Conclusions: Our findings demonstrate that carvacrol modulates liver gene expression and metabolic profiles, primarily influencing amino acid and lipid metabolism pathways, autophagy, and stress responses. The observed correlations between dnaja3b and specific metabolites offer mechanistic insights into the action of carvacrol in fish liver.

Objectives: This study aimed to investigate the regulatory effects of dietary carvacrol on intestinal micro biota composition, serum metabolic profiles, and their association with increased resistance to Aeromonas hydrophila in Pengze crucian carp. Methods: Juvenile fish (5.63 ± 0.35 g) were randomly allocated into two experimental groups: a control group (CK) fed a basal diet and a treatment group (CA) supplemented with 600 mg/kg microencapsulated carvacrol. Following an 8-week feeding trial, nine specimens per group were sampled for venous blood and intestinal tract collection. Remaining individuals were subjected to a 12-h A. hydrophila challenge prior to identical sample collection. Results: Key findings revealed that carvacrol supplementation induced significant microbial modulations, notably reducing Firmicutes abundance while enhancing Cetobacterium populations by 33.25% compared to controls. Post-challenge analysis demonstrated marked declines in intestinal microbial diversity indices (Observed ASV, Chao1, ACE, and PD whole tree) in the CK group, whereas the CA group maintained stable microbial diversity. Pathogenic genera including Aeromonas, Shewanella, and Vibrio showed significant proliferation in challenged controls, contrasting with maintained microbial homeostasis in carvacrol-fed specimens. Serum metabolomic profiling identified the most significantly altered metabolic pathways associated with carvacrol administration: glycerophospholipid metabolism, linoleic acid metabolism, arachidonic acid metabolism, α-linolenic acid metabolism, GPI-anchor biosynthesis, and autophagy-animal pathways. Conclusions: Our results demonstrate that dietary carvacrol may reinforce intestinal microbial barrier function by optimizing beneficial microbial composition and reducing the proportion of pathogens, and modulate immune-related metabolic pathways critical for host defense, which might be involved in enhanced disease resistance.

This study was designed to assess the protective efficacy of dihydromyricetin (DHM) against intestinal injury in Chinese soft-shelled turtles (Pelodiscus sinensis) caused by partial replacement of fishmeal (FM) with fermented rapeseed meal (FRM), and to uncover the molecular mechanisms involved. Turtles were fed an FM-based control diet, an FRM-substituted diet, or FRM diets supplemented with DHM at 0.5‰ (DHMT1), 1.0‰ (DHMT2) or 2.0‰ (DHMT3) for 8 weeks. Growth performance, digestive enzyme activities, antioxidant parameters, inflammatory cytokines, and intestinal histomorphology were assessed, and intestinal transcriptomics and metabolomics were also performed. FRM replacement significantly improved growth performance; however, this beneficial effect was accompanied by notable intestinal mucosal oxidative damage, as evidenced by decreased villus height, increased lumen space, and lamina propria edema, along with elevated pro-inflammatory cytokines (IL-1β and TNF-α) and MDA content, alongside reduced GSH and CAT activities. DHM supplementation dose-dependently ameliorated these adverse effects by restoring mucosal integrity, digestive enzyme activities, redox homeostasis, and inflammatory balance, ultimately improving growth performance. Transcriptomic KEGG analysis revealed that DHM enriched pathways related to glycerophospholipid metabolism, glutathione metabolism, drug metabolis-cytochrome P450, and polyunsaturated fatty acid metabolism. Metabolomics further confirmed dose-dependent remodeling of phospholipids and bile acids. Integrated omics demonstrated that DHM likely regulates detoxification, anti-inflammatory, membrane repair, and antioxidant pathways. In conclusion, DHM demonstrates a protective effect against FRM-induced intestinal mucosal oxidative damage in P. sinensis, which may be mediated by a synergistic combination of enhanced detoxification, anti-inflammatory modulation, restoration of phospholipid membrane integrity, and reinforcement of antioxidant defenses.