Abstract
Heat stress negatively affects the growth and health of fish. In this study, Eurasian perch ( Perca fluviatilis ) were exposed to control (18°C, CK) and heat stress (25°C, HS) conditions. Using liver transcriptomics and metabolomics in conjunction with physiological and biochemical indicators, we investigated the mechanisms underlying their thermal response. The results revealed that heat stress in P. fluviatilis led to liver cell damage, characterized by vacuolar degeneration and inflammatory cell infiltration. Heat stress caused a fluctuating decrease in superoxide dismutase (SOD) activity, a significant reduction in catalase (CAT) activity ( p P. fluviatilis . This study provides a basis for understanding the hepatic responses of temperate freshwater fish to elevated temperatures.