Ika-Tere

In Māori & Polynesian mythology, Ika-tere is the fish god, the father of all the sea creatures including mermaids.
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[Polynesian] The most common name for the Polynesian fish-god. He is the father of fish, grandson of the ocean-god Tangaroa. He begot all the animals that live in the sea and rules them with wisdom. Some of his children were partly human, like mermaids and merman, although often the right side was fish while the left side was human. Gradually they became all-human.