Countercurrent exchange fish employ a unique circulatory system to regulate body temperature in water. Their gills contain parallel vascular networks, allowing warm arterial blood from the body to flow in close proximity to cold venous blood returning to the gills. The temperature gradient between these opposing streams of blood promotes heat transfer, maintaining body temperature even in colder environments. This heat exchange system enables fish to conserve energy, efficiently deliver oxygen to active muscles, and survive in diverse aquatic conditions.
