The first planet seen outside our own solar system, Fomalhaut B. Fomalhaut means "mouth of the (big) fish", translated from Arabic (fum al'hot). Since my mythological education was greco-roman centric, it's good to learn a new myth from a different religion/culture. Here's a snippet from related stories about the big fish, the star, and the mermaids:
"In Greek mythology, Fomalhaut was associated with the monster Typhon, who is said to lie buried beneath Mt. Etna in Sicily. In Syrian and Canaanite lands it was honored as the symbol of the fish-god Dagon, whose temple at Gaza was destroyed by the Biblical strongman Samson. This temple is believed to have been oriented to the rising of Fomalhaut.
All accounts of this constellation's mythology are disappointingly sketchy. Like Pisces, its mythology has a Middle Eastern setting indicative of Babylonian origin. An ancient constellation, Piscis Austrinus represents the Babylonian fish-god Oannes, who came to Earth to teach humans how to become civilized. According to the brief account of Eratosthenes, the Syrian fertility goddess Derceto (the Greek name for Atargatis) is supposed to have fallen into a lake at Bambyce near the Euphrates river in Syria, and was saved by a large fish. Hyginus says, in repetition of his note on Pisces, that as a result of this the Syrians do not eat fish but rather they worship the images of fish as gods.
Bambyce later became known to the Greeks as Hieropolis (meaning Sacred City), now called Membij. Other classical sources tell us that temples of Atargatis contained fish ponds. The goddess was said to punish those who ate fish by making them ill, but her priests ate fish in a daily ritual.
According to the Greek writer Diodorus Siculus, Derceto deliberately threw herself into a lake at Ascalon in Palestine as a suicide bid in shame for a love affair with a young Syrian, Caystrus, by whom she bore a daughter, Semiramis. Derceto killer her lover and abandoned her child, who was brought up by doves and later became queen of Babylon. In the lake, Derceto was turned into a mermaid, half woman, half fish. So merpeople may also be associated with the constellation Piscis Austrinus."
- Mythology of Star Tales, Ian Ridpath. Universe Books, New York.