Abstract: This study mainly analyzed the effects of Cornus officinalis extract (COE) on growth performance, serum lipid metabolism and tissue antioxidant capacity of Micropterus salmoides (largemouth bass) under high saline or high alkaline stress. A total of 360 juvenile largemouth bass with an initial body weight of (30.27±0.11) g were randomly divided into six groups for a 60 days feeding trail: freshwater group (C), freshwater + 0.5% COE group (COE), saline group (S, 8.5 NaCl-induced salinity), saline + 0.5% COE group (SCOE), alkaline water group (CA, 15mmol/L alkalinity from NaHCO₃ solution), and alkaline water + 0.5% COE group (CAC) l. Liver, gill and kidney morphology was examined using hematoxylin-eosin staining. Additionally, the growth, proximate composition, serum biochemical indexes and related enzyme activities were detected in the largemouth bass. Compared with the freshwater control group (C), exposure to high saline (S) or high alkaline (CA) stress significantly reduced the food intake and growth performance of largemouth bass (P < 0.05). While supplementation with 0.5% COE did no significantly improve final body weight (P > 0.05), it significantly alleviated the tissue damage caused by stress, including hepatocyte vacuolization, gill filament bending and glomerular atrophy/swelling. Analysis of serum biochemical indicators revealed the protective effects of COE under stress conditions. Compared with the stress control group (S group or CA group): ① Under high saline stress, the activities of serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in the SCOE group were significantly reduced (P < 0.05), suggesting an alleviation of liver damage; ② The serum triglyceride (TG) content of the SCOE group was also significantly reduced; ③ The gill Na⁺/K⁺-ATPase (NKA) activity in the SCOE group was significantly decreased, indicating a reduction in osmotic pressure. Regarding antioxidant capacity, high saline/alkaline stress changed the antioxidant enzyme activity spectrum of liver, gill and kidney. The addition of COE under both high-salt and high-alkali conditions can significantly enhance the total antioxidant capacity (T-AOC) of the kidneys (P < 0.05), and the superoxide dismutase (SOD) activity of gill filament was significantly increased under high alkaline conditions (P < 0.05). The inclusion of 0.5% COE in the diet mitigated the negative effects of high saline or high alkaline stress on largemouth bass by improving serum lipid metabolism, reducing tissue lesions and enhancing antioxidant defense, this study provides a theoretical basis for the application of COE in saline-alkali aquaculture of largemouth bass.