Physiological Effects, Molecular Regulation, and Adaptive Strategies of Heat Stress in Fish Under Global Warming

Heat stress is one of the most prevalent and unavoidable environmental stressors in modern aquaculture and natural fishery ecosystems. With the intensification of global warming, the frequency, intensity, and duration of extreme heat events have increased substantially, progressively reducing the thermal safety margin of fish. As ectothermic vertebrates, fish rely heavily on ambient water temperature to maintain physiological functions and metabolic homeostasis. Elevated temperatures can induce profound metabolic reprogramming, characterized by suppressed protein deposition, enhanced lipid mobilization, and altered glucose metabolism, while simultaneously causing structural damage and functional dysfunction in critical organs and tissues such as the liver, intestine, gills, and reproductive system. Heat stress also activates the stress axis and oxidative stress responses, often leading to immunosuppression and disruption of antioxidant defenses, ultimately impairing growth performance, behavior, reproduction, and survival. This review focuses on fish and summarizes the major physiological injuries, molecular regulatory pathways, and adaptive strategies associated with heat stress under global warming. Comparative evidence from crustaceans and molluscs is used only where it helps clarify shared or divergent responses among aquatic ectotherms.