Cameos, in-jokes, re-used animation and other trivia from Finding Nemo.
- During the preview of the escape plan, the Pizza Planet truck drives past.
- During the closing credits, Mike Wazowski snorkels by.
- A boy in the dentist's waiting room is reading a Mr. Incredible comic book.
- The dentist office waiting room includes a Buzz Lightyear toy on the floor.
- At the end, when the fish are escaping from the dentist's office, a car similar to Luigi from Cars drives past.
- Along with Buzz Lightyear, many other references from previous Pixar films make a cameo around a toy box in the dentist's office. These include:
- One of the boats in Sydney Harbour is called "For the Birds", a reference to the short For the Birds.
- A113 appears as a model code on the camera used by one of the scuba divers.
- Sunny Atlantis from Knick Knack appears on the shipwrecked ship in the tank.
- Boo's fish mobile from Monsters, Inc. appeared in the dentist's office.
- The Pixar University certificate was seen in the waiting room.
- When Marlin and Dory ask the school of fish for directions to get to Sydney, the scene is similar to the scene in the movie's own teaser trailer.
- The film's prominent use of clownfish prompted mass purchase of the animals for children's pets in the United States, even though the movie portrayed the use of tropical fish as pets negatively and that saltwater aquariums are notably tricky and expensive to maintain. As of 2004, in Vanuatu, clownfish were being caught on a large scale for sale as pets, motivated by the demand.
- The movie is the first ever movie to get a PG rating from the MPAA in New Zealand.
- In the fullscreen version of the film, you can actually see the visible portion of a female patient's legs (they are hidden under her skirt) as she is entering the waiting room and is mistaken for Darla. Unfortunately, this is only present in the 2003 US original home video release, as the Blu-ray release as with the international versions of both releases only contains the widescreen version. However, her legs are still visible even in that version, but she (and her son, see cameo of Mr. Incredible above) were sitting.
- This is one of Pixar's first attempt at animating realistically-flowing skirts and/or dresses on women, with the example being above.
- This is the first Pixar film to take place in a country other than the United States, instead taking place in the seas surrounding the eastern half of Australia, with the second being Ratatouille (France), the third being Cars 2 (multiple locations such as Japan, France, Italy, and the United Kingdom, though the United States can be seen in the opening and ending), and the fourth being Brave (Scotland).
- When Dory found the whale, she wanted to ask it directions whereas Marlin doesn't. Then Dory asks him, "What is it with men and asking directions?" This quote was also said in Mulan 2.
- This is the last Pixar film to have its fullscreen and widescreen formats in the same DVD case, but also the first to have them on separate DVDs, both in the same case. It should also be noted that this applies to the US version only, since the international version contains only the widescreen version and Disc 2 is made up of mostly bonus features.
- Although the film featured realistically-animated water, said water was slightly animated less realistically to avoid people confusing said water for live footage of the ocean.
- Although this movie portrays the idea that fish that are flushed down the drain are returned to the ocean unharmed, in reality this is not the case. In reality, though any water that goes down a drain does reach the ocean eventually, it will first go through equipment that breaks down solids, meaning that Nemo would have been killed long before being released into the sea. A company that manufactures such equipment put out a warning to prevent kids from flushing their fish thinking they were 'releasing' them (noting that in reality, they were Grinding Nemo). A planned scene would have shown Nemo in the sewage plant somehow avoiding the grinding machinery (Nemo getting into the filter to jam it would have been a foreshadowing of this), but this was cut for time and pacing.
- This is Pixar's first film to be released in cinemas in the northern hemisphere summer.
- Although unintentional, the names of Tad and Pearl's fathers, Bill and Ted, could be a reference to the film Bill and Ted's Excellent Adventure.
- The film is one of Pixar's first attempt at animating "realistic" human characters (animated humans that sport mostly realistic body proportions, but with some slightly exaggerated anatomical structures, particularly their facial features especially their eyes and their hands and feet), their depiction of "realistic" when it comes to animating humans refers to how they draw them in a way so that they all avoid falling into the "uncanny valley".
- This is the last Pixar film starring Joe Ranft in the main cast to be released when Ranft was still alive. Ranft was nowhere to be seen in The Incredibles, and he dies a car accident in 2005, during production of Cars.
- This is the first Pixar film to win the Best Animated Feature Award. Monsters, Inc. was nominated, although it lost to Shrek.
- 12,996 individual corals were used to build the reef that Mr. Ray’s class swims through.