Opening on May 30, 2003, Finding Nemo is written by Andrew Stanton, directed by Stanton and Lee Unkrich and produced by Pixar Animation Studios. It tells the story of the overly protective clownfish Marlin who along with a regal tang called Dory searches for his son Nemo. Along the way he learns to take risks and that his son is capable of taking care of himself.
Marlin, an Ocellaris clownfish, takes extra care of his only child, Nemo, after his wife Coral and the rest of their eggs were eaten by a barracuda. Due to a crack in Nemo's egg, he has grown up with one small, weak fin, but which Marlin assures him is his "lucky fin". On the first day of school, the other kids tease Nemo about his overprotective widower father. Nemo decides to swim into the open waters to prove that he is capable but is quickly captured by a scuba diver, who climbs aboard a boat and drives off. Marlin is unable to keep up after a frantic chase but meets Dory, a regal tang with short-term memory loss. Together they discover a diver's mask on the ocean floor dropped from the boat, and Dory is able to read the address on it as being Sydney, Australia. The two set off; Marlin's story of determination quickly spreads about the oceans, and various sea creatures give aid to his search.
Meanwhile, the diver, a dentist, returns to his office and places Nemo in a fish tank. Nemo meets the other fish, led by the moorish idol Gill. When they realize that the dentist plans to give Nemo to his niece Darla, who has had a fatal history of dealing with pets before, they devise a plan to help free Nemo by forcing the tank to become dirty, requiring the dentist to remove the fish and allowing for their escape. The plan requires Nemo, the smallest of them, to swim up the water filter and disable it; the first attempt is nearly fatal for Nemo, but is able to succeed on a second attempt when he hears from Nigel, a brown pelican, that Marlin is coming for him. However instead of taking the fish out of the tank the Dentist instead installs a high-tech laser-scanning filter which automatically cleans the tank while the fish are sleeping.
After several adventures, Marlin and Dory arrive in Sydney and are met by Nigel, who recognizes and takes them to the dentist's office, but find the dentist is already getting ready to give Nemo to Darla. Nemo acts dead as to force him to be flushed down the drain and eventually into the sea, but this also causes Marlin to believe him to be dead. After Nigel's presence in the office causes a small pandemonium, Gill helps Nemo to escape down a drain.
Despite the fact that Dory claims to have better memory when around him, Marlin tells Dory to leave him alone once they are back in the sea. Dory swims off but encounters Nemo; though temporarily confused due to her memories, she eventually remembers Marlin's goal, and helps Nemo back to his father. The two, along with Dory, happily celebrate, but their joy is quickly cut short when Dory is caught, along with a school of grouper, in a fishing net. Despite Marlin's worries, Nemo swims to help the fish, including Dory, escape using a trick taught to him by Gill and the other aquarium fish. The three return back home, with Marlin less protective of Nemo now aware of his son's abilities; Nemo's stories of his adventures impress the other children, while Marlin is seen as an outstanding father by the other fish.
Meanwhile, Gill and the other fish from the dentist's office have managed to make their escape via their original plan, ending up safely in the ocean but still trapped in plastic bags.
In an interview with National Geographic magazine, Andrew Stanton stated that the idea for the character of Nemo came from a photograph of two clownfish peeking out of an anemone:
"It was so arresting. I had no idea what kind of fish they were, but I couldn't take my eyes off them. And as an entertainer, the fact that they were called clownfish—it was perfect. There's almost nothing more appealing than these little fish that want to play peekaboo with you."
Pre-production of the film took place in early 1997. Film production began in January 2000 with a crew of 180.