To investigate the physiological adaptive processes of black amur bream （Megalobrama terminalis） under acute high-temperature stress， this study analyzed changes in tissue structure， serum biochemical indices， and antioxidant enzyme activities at different time points （0 h， 8 h， 16 h） under stress temperatures of 28 ℃ （control group）， 32 ℃， and 36 ℃. The results showed that acute high-temperature stress significantly affected the physiological homeostasis of blunt snout bream. As the stress temperature increased （32 ℃， 36 ℃）， liver tissue damage intensified， manifested as cytoplasmic loosening， nuclear atrophy， and vacuolization of hepatocytes. Serum biochemical analysis revealed that the activities or concentrations of Total Protein （TP）， Triglycerides （TG）， Total Cholesterol （TC）， Aspartate Aminotransferase （AST）， Alanine Aminotransferase （ALT）， Alkaline Phosphatase （ALP）， and Cortisol （COR） generally increased significantly with rising temperatures， demonstrating pronounced metabolic and functional disturbances. Serum COR levels decreased with prolonged stress duration in the high-temperature groups， indicating exhaustion of the adrenal stress response under sustained heat. Liver antioxidant enzyme activities—Superoxide Dismutase （SOD）， Catalase （CAT）， and Glutathione Peroxidase （GPx）—also increased with rising temperatures but followed an initial rise followed by a decline pattern with prolonged stress duration， suggesting potential inhibition of the antioxidant defense system after an initial activation phase. This study found that acute high-temperature stress （especially above 32 ℃） can significantly damage the structural integrity of tissues， disrupt serum biochemical balance， and induce a stress response in the antioxidant system of blunt snout bream， ultimately leading to significant physiological dysfunction. These findings suggest that prolonged acute high-temperature environments above 32 ℃ should be avoided during blunt snout bream farming， providing crucial physiological insights for optimizing health management strategies in high-temperature environments.