Triton of the Sea (1979)

Some time ago, the evil Poseidon destroyed the continent of Atlantis and all of its inhabitants - except for two: the green-haired baby Triton, and the mermaid Pipi. Triton was brought by the white dolphin Ruka to the shore of a fishermen's village; and there, he was raised by a kind man for thirteen years. However, the time has come for Triton to learn the truth about his heritage, the death of his parents at the hands of Poseidon, and what he must do henceforth: track down Poseidon and bring peace to the seas again. With the help of Ruka, Pipi and other aquatic friends, Triton sets forth to fulfill his destiny.