In Hans Christian Andersen’s “The Little Mermaid,” the Sea King has six daughters. The unnamed mermaid who gives the tale its title is the youngest of the six sisters, and the story describes her as the prettiest and most curious. Their grandmother helps care for them in the Sea King’s underwater palace, where the sisters grow up surrounded by coral, amber, and the sea’s wonders.
Each daughter waits until she reaches the required age before swimming to the surface to see the human world. The older sisters tell the youngest about their experiences above the waves, increasing her longing to visit the surface herself. Their family relationship is part of the original 1837 fairy tale and is not presented with the individual names used in some later adaptations.
This detail is often confused with Disney’s version. Disney’s Ariel has six older sisters, meaning Triton has seven daughters in total. Andersen’s original mermaid is one of six daughters altogether, so “six” is the correct answer for the question’s explicitly stated version. The original tale is also darker than the animated film: the mermaid gives up her voice and ultimately becomes a spirit known as a Daughter of the Air.