Fish and amphibians are two groups of animals with different circulatory systems. Fish have a single-loop circulatory system, where the heart pumps blood in one direction through the gills to the body and then back to the heart. This system is efficient for extracting oxygen from water. In contrast, amphibians have a double-loop circulatory system, with a three-chambered heart that separates oxygenated and deoxygenated blood. This allows amphibians to breathe through their lungs and skin, and to live both in water and on land. Despite these differences, both fish and amphibians rely on their circulatory systems to deliver oxygen and nutrients to their cells and remove waste products.