Adaptation to extreme environments: A review of Antarctic fish physiology

Having evolved in the chronically cold and thermally stable waters of the Southern Ocean (SO) for millions of years, Antarctic fish possess a suite of physiological specializations that enable them to survive at temperatures near the freezing point of seawater. Adaptations include the evolution of antifreeze proteins, modifications of membrane composition, altered metabolic processes, unique mechanisms of oxygen transport and utilization, and distinctive cellular stress responses. This review synthesizes current knowledge of the physiological adaptations of Antarctic fish, focusing on the mechanisms that support survival in extreme cold environments. We examine adaptations related to cold tolerance, osmoregulation, metabolism, reproduction, sensory biology and oxygen transport and discuss the evolutionary processes that have shaped these traits. We further evaluate how ongoing climate-driven changes, including ocean warming, acidification and biological invasions, may affect Antarctic fish populations and ecosystems. Understanding the physiological foundations underlying Antarctic fish adaptation provides important insights into evolutionary responses to environmental extremes and provides a framework for predicting potential vulnerabilities of polar marine organisms in a rapidly changing world.