It was in fact My favorite Mermaid Movie of all time!! :D
I love Sophia, The Mermaid Princess of "The Planet Aqua", who ends up landing on Nobita's and Doraemon's backyard, thinking She's so cute and beautiful! XD
It always reminds me of Ariel from Disney's Little Mermaid (1989) and Ripjaws from Ben 10! XD
Sophia from Doraemon, according to the Japanese Wikipedia says that She might have been inspired by Hans Christian Andersen's The little Mermaid from Denmark in 1837.