In 1841, P.T.Barnum discovered a curiosity brought from the South Seas called, as we know, the "Fiji Mermaid", becoming one of his greatest successes in the art of hoax.
Grace to a time still prived by photography, peoples was obliged to believe in drawings, and impresarios could speculate about their promises. Here, you see how the mermaid was announced (left), and the later famous artifact that you in reality saw once inside (right).
But less is known about the origins and previous iconography of the creature we know as "Fiji Mermaid", before Barnum revealed it to the world. Here is a japanese drawing, far older than Barnum himself.
You can learn more about the oriental origins of mermaids, from a wonderful documentation of Takeshi Yamada, "visual anthropologist", recently posted on www.sideshowworld.com.