Why are mermaids half fish?

Mermaids are depicted as half fish primarily due to their origins in folklore and mythology, where they represent a blend of human and aquatic qualities. This combination symbolizes the allure and mystery of the ocean, bridging the gap between the human world and the depths of the sea. The fish tail allows for graceful movement in water, while the human upper body embodies traits such as intelligence and emotion, enhancing their role as enchanting yet often perilous creatures in stories.