An 8-week feeding experiment was carries out to explore the impacts of dietary tauroursodeoxycholic acid (TUDCA) on growth and gut integrity in spotted seabass (Lateolabrax maculatus) under heat stress (33 °C). Three hundred fish (2 ± 0.02 g) were allocated to triplicate groups and fed five diets containing graded levels of TUDCA at 0, 10, 20, 30, or 40 mg/kg (designated as Con, T10, T20, T30 and T40 diets). Growth performance was significantly (P < 0.05) enhanced in fish receiving ≥30 mg/kg TUDCA compared to the control group. Progressive increases in intestinal total antioxidant capacity and superoxide dismutase activity, accompanied by decreased malondialdehyde concentration, were observed as TUDCA dose increased. TUDCA application modulated the expression of intestinal antioxidant-related genes, downregulating keap1 and upregulating nrf2. Notably, supplementation with 40 mg/kg TUDCA improved intestinal morphology, as evidenced by increased villus height and number. Furthermore, in the T40 group, a marked downregulation of pro-apoptotic genes (caspase3, caspase8, caspase9, and bax) and reduced immunofluorescence intensity were observed, while the expression of the anti-apoptotic gene bcl was significantly up-regulated. Additionally, the expression of pro-inflammatory genes (il-1β, il-8, and tnf-α) and immunofluorescence intensity were significantly reduced in the T40 group compared to control. In contrast, the expression of anti-inflammatory genes (il-4, il-10, and tgf-β) was markedly upregulated. Furthermore, dietary inclusion of 40 mg/kg TUDCA suppressed the expression of endoplasmic reticulum stress-related genes (grp78, chop, perk, atf6, and ire1) and activated the bile acid receptor gene tgr5 in the intestine. Concurrently, TUDCA treatment enhanced the PI3K-Akt signaling pathway, contributing to the inhibition of apoptosis. The data generated in this study demonstrated that dietary supplementation with 40 mg/kg TUDCA promotes growth, activates the Nrf2-Keap1 and PI3K-AKT signaling pathways, enhances intestinal antioxidant defenses, suppresses inflammation and apoptosis, alleviates endoplasmic reticulum stress, and mitigates the physiological impacts of heat stress in L. maculatus reared at elevated temperatures.

Faculty of Fisheries and Protection of Waters University of South Bohemia in České Budějovice South Bohemian Research Centre of Aquaculture and Biodiversity of Hydrocenoses Vodňany 389 25 Czech Republic

State Key Laboratory for Mariculture Breeding Fisheries College Jimei University Xiamen 361021 China

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