There are many references to Richard Wagner's opera series 'Der Ring des Nibelungen' scattered throughout the film. Ponyo's real name is Brünnhilde, one of the leading roles of Wagner's 'Die Walküre.' Brünnhilde is also a "supernatural," being who falls in love with a human (Siegfried), much like Ponyo falls in love with Sôsuke. When Ponyo is chasing after Sôsuke and his mother during the giant storm scene, you can hear a musical tribute to Wagner's "Ride of the Valkyries."
Hayao Miyazaki drew most of the sea and wave imagery himself, experimenting with making it as expressionistic as possible. John Lasseter said that he had never seen water animated so beautifully before.
In 2009, the film's US gross ($15 million) set a record for a Disney/Ghibli production. Only five other anime films have grossed more in the US: three of them being Pokémon films, the fourth Yu-Gi-Oh!: The Movie (2004), and the fifth The Secret World of Arrietty (2010) (another Disney/Ghibli production).
The trivia item below may give away important plot points.
The sequence in which Ponyo offers food to the baby was included to show that Ponyo could be selfless and live in the human world. Hayao Miyazaki developed the scene late in production, when he was stuck on how to end the film.