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.
The opening twelve seconds, involving vast schools of fish and undersea creatures, required 1,613 pages of conceptual sketches to develop.
Hayao Miyazaki was very surprised by the lukewarm reaction of children to his film in test screenings.
The level of detail in the animation resulted in 170,000 separate images - the most that have ever appeared in a Hayao Miyazaki film.
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."
This is the first animated feature film since Princess Mononoke (1997) to be created and painted on traditional animation cels.
Hayao Miyazaki stated at the 2009 San Diego Comic Con that he was inspired to create the film after watching Disney's animated adaptation The Little Mermaid (1989).
The seaside village where the story takes place is inspired by the town of Tomonoura in Setonaikai National Park in Japan where Hayao Miyazaki stayed in 2005.
Melissa Matheson, the writer of E.T. the Extra-Terrestrial (1982), revised the English translation for the American version.
Sôsuke's father works aboard a ship named the Koganei maru. Koganei is the town in Western Tokyo where Studio Ghibli is located.
In 2009, the film's U.S. gross (fifteen million dollars) set a record for a Disney/Ghibli production. Only five other animé films have grossed more in the U.S., three of them being Pokémon films, the fourth Yu-Gi-Oh!: The Movie - Pyramid of Light (2004), and the fifth The Secret World of Arrietty (2010) (another Disney/Ghibli production).
This was the first animated film to be nominated for and win the Best Film Score prize at the Japanese Academy Awards.
Until The Secret World of Arrietty (2010), this received the widest release for a Studio Ghibli film in the U.S., when it opened in 927 theaters. Spirited Away (2001) opened in 26 theaters, Howl's Moving Castle (2004) 36, and Princess Mononoke (1997) 38.
Melissa Mathison wrote the English language script in just four days, but also worked with the actors during the voice-over sessions, to further refine the translations.
Hayao Miyazaki was interested in doing a sequel to the film, but Producer Toshio Suzuki suggested Miyazaki adapt The Wind Rises (2013) instead.
The design of the ocean waves, during the typhoon caused by Ponyo, were inspired by the waves in the famous woodblock print The Wave Off Kanagawa by Japanese artist Hokusai.
The first Hayao Miyazaki film to be rated G by the MPAA since the release of Kiki's Delivery Service (1989) in 1998.
Sôsuke is a reference to the works of famous Japanese novelist 'Sôseki Natsume' (1867-1916). In 'The Gate,' central male character Sôsuke lives in a house that stands on a hill, Gake no ue.
A sequel was planned, but was swapped with The Wind Rises (2013), and since Miyazaki's retirement, it's unknown if it's still going to be made.
When Lisa sings, "I'm happy as can be", it is to the tune of the My Neighbour Totoro theme music.
When Ponyo first becomes human, she recreates giant waves of tsunamis, and Ponyo is shown running on them all the time, because of her magic. Later in the film, when Ponyo makes Sosuke's boat bigger, she runs outside to the water with Sosuke, to put the boat in the water, when she first runs outside, if you look, you can see her walking a few feet out of the house onto the water. But only after taking a few steps outside, she then sinks into the water, this shows that Ponyo's magic is getting weaker, which is shown more, later in the movie.
Ponyo's hair is up when she uses magic, or when she has magic, but is down when she is tired or out of magic.
Judging by what her dad says about her drinking blood, it could be that Ponyo has been human before.
When she's a fish, she has a white belly spot, but when she's human, it isn't there, but when Ponyo makes the boat big, when her shirt flies up, you can see a faint belly spot.
The design of the ocean waves during the typhoon caused by Ponyo were inspired by the waves in the famous woodblock print The Wave Off Kanagawa by Japanese artist Hokusai.
In the beginning intro of the film, the Music Composer of the film, Joe Hisaishi's name is credited behind a pink ocean, which is not given to any other names.
When Ponyo is dragging the boat into the water, she can briefly walk on water, but soon sinks into the water.
It's unknown, that before she became human permanently, if she could change clothes, or take off the ones she had.