Pixar's characters are often planned years in advance. Nemo first appeared as a stuffed toy on a couch in Boo's room in Monsters, Inc.. This movie introduces the main characters of post-2003 Pixar films. A boy in the dentist's office is reading a "Mr. Incredible" comic book, anticipating The Incredibles. Luigi the car is driving by the dentist's office, anticipating Cars.
According to the DVD, the names of the nine boats seen in the Sydney harbor are: Sea Monkey, Major Plot Point, Bow Movement, iBoat (a reference to iTunes, the company created by Pixar CEO Steve Jobs), Knottie Buoy, For the Birds, Pier Pressure, Skiff-A-Dee-Doo-Dah (a reference to Song of the South's most famous song "Zip-a-Dee-Doo-Dah"), and The Surly Mermaid.
Afraid that kids would try releasing their pet fish by flushing them down a drain, a company that manufactures equipment used by water filtration and sewage treatment plants released a warning the Thursday after the film came out saying that, even though drains do eventually reach the ocean, before it got there the water would go through equipment which breaks down solids, and went on to say that in real life the movie would more appropriately be called "Grinding Nemo".
Albert Brooks was always Andrew Stanton's first choice to voice the part of Marlin. Although Brooks had done several episodes of The Simpsons, he found voice work for a feature length cartoon to be substantially different in that he had to do it in isolation, and not alongside any other actors. He didn't particularly enjoy the experience.
The look and feel of the underwater world was essential to the film's success. To that end, the production crew were all exposed to visits to aquariums, diving stints in Monterey and Hawaii, study sessions in front of Pixar's own 25-gallon fish tank and even a series of in-house lectures from an ichthyologist.
Andrew Stanton pitched his idea and story to Pixar head John Lasseter in an hour-long session, using elaborate visual aids and character voices. At the end of it, the exhausted Stanton asked Lasseter what he thought, to which Lasseter replied, "You had me at 'fish'."
To see how realistic they could make it appear, the art team were asked to make exact copies of actual underwater and above-water shots. Ultimately the results were simply deemed "too realistic" for a cartoon.
According to the DVD, there are some references to Massachusetts in the film as one of the creators is from Rockport, Massachussetts. While various sea creatures are relating Marlin's quest across the ocean, one step is a group of lobsters that speak with Boston accents and slang ("wicked daahhk").
Though never mentioned in the film, it is revealed by the directors in the commentary that Crush and his crew of thrill-seeking turtles are headed for Hawaii. Also mentioned in the commentary is that the young turtles' shells are modeled after Hawaiian shirts.
Rendering a frame which lasted about 1/24th of a second in the film could take up to four days because of the complexity of the underwater environment with sunlight coming through the water and hitting fish scales.
Director Andrew Stanton originally planned to reveal the fate of Marlin's wife gradually through flashbacks seen periodically as the story unfolded. After a few early in-house screenings, he found that Marlin came off as too much of a worrywart, and decided to reveal the entire back-story up front, thus making Marlin more appealing by establishing the reason for his over-protectiveness.
In the original cut of the movie, the whale that swallows Marlin and Dory approaches them from the front. This version of the scene appeared in an early trailer. The final version, with the whale coming from behind, was inspired by an early animation test showing a whale emerging from the murk of the ocean behind a small fish.
Per the DVD extras, Albert Brooks spent an entire day in the recording studio improvising badly mangled versions of the anemone joke; no two tellings were fumbled in the same way. He had the recording technicians in stitches for the duration.
Dory does get Nemo's name right a total of 7 times, 4 of them without being corrected first. Of course some of these times are in quick succession. She also calls him Chico, Fabio, Bingo, Harpo, and Elmo, in that order.
Megan Mullally revealed that she was originally doing a voice in the film. According to Mullally, the producers were quite disappointed to learn that the voice of her character Karen Walker on the television show _"Will and Grace" (1998)_ wasn't her natural speaking voice. The producers hired her anyway, and then strongly encouraged her to use her Karen Walker voice for the role. When Mullally refused, she was fired.