They're only toys: cuddly cloth cowboys, adorable insects, furry monsters. But when the pixilated storytellers at Pixar fashion them, these playthings come to life. Take Marlin, the single-dad clown fish, voiced by Albert Brooks, in the new Pixar astonishment Finding Nemo. Brooks says that when a reporter on a junket described this fish father as overprotective, "I stood up and said, 'Overprotective? If your wife and almost all your children were eaten by a shark, you wouldn't be overprotective?' Then I realized — I'm yelling about a fish."

Of course, Marlin is not even a fish. He's a computer-generated image attached to a famously fretful voice. But Marlin has all-too-human qualities: insecurity, suspiciousness, giant wrinkles of worry and a lot of saving heart. Endearing flaws like these, along with an unmatched graphic elegance and elfin wit, have made Pixar's first four features — Toy Story, A Bug's Life, Toy Story 2 and Monsters, Inc. — the gold standard in computer-generated imagination. Gold, as in $1.73 billion worldwide gross for that quartet, plus truckfuls more in video and DVD profits. Pixar owner Steve Jobs will need a battleship to hold all the money his current distribution partner, Disney, will need to fork over to renew their contract, which expires in 2005. The two studios now split the profits from Pixar movies, but since Pixar's CGI movies have been grossing nearly twice what the Mouse House's own animated films take in, Jobs wants a more grownup portion of the money.

While the Pixarians aren't really boys, they are guys (all the top creative types are male) who radiate a benign youthfulness. The company, with headquarters in Emeryville, Calif., outside San Francisco, is a giant playpen, a kind of Erector-set tree house. Games and gadgets clog the office of head Pixie John Lasseter, whose uniform is a blindingly gaudy Hawaiian shirt. Nemo's begetter, Andrew Stanton, 37, looks a dozen years younger and decades more innocent. He, Lasseter and the rest seem like boys in love with their computer toys.

But these seraphic-faced artists are working stiffs and parents too. The Toy Story tandem and A Bug's Life were clever parables of workplace camaraderie. And the two most recent Pixar films are stories of not-quite-mature men (in the guise of monsters or clown fish) who learn the onerous joys of fatherhood. Like many classic Disney cartoons, and Spielberg fables, Finding Nemo is about the traumatic separation of a child from his parent. The refreshing difference here is that Nemo dramatizes the anxiety (and adventures) a parent undergoes searching for his wayward, precious kid.

Long before Nemo comes along, Marlin is a fussy little anxiety machine. When he learns he's to be a father — of 400 baby clown fish — he fidgets: "What if they don't like me?" But he's right to be concerned for his brood in the fish-eat-fish world of Australia's Great Barrier Reef. A shark devours Marlin's wife and 399 of her eggs. That leaves little Nemo (Alexander Gould)--the one survivor, handicapped with an underdeveloped fin — and Marlin, burdened with an overdeveloped sense of dread. When Nemo is old enough for fish school, Dad's pessimism is again validated: the lad defiantly swims into open water, where he is scooped up by an angler — a dentist, with an aquarium in his office and a nasty, piscicidal little niece he can't wait to give this cute clown fish to.

Marlin, who must now conquer his own fear of the great wet world, that "swirling vortex of terror," has a companion in his search: Dory (Ellen DeGeneres), a blue tang with a sunny disposition and a short-term memory problem. In their hunt for Nemo, they are aided and threatened by all manner of sea creatures: a menacing anglerfish, some not entirely trustworthy members of Sharks Anonymous, a school of shocking jellyfish and a family of surfer-dude sea turtles. In captivity, Nemo finds his own friends: Peach, the starfish (Allison Janney), and the tank commander Gill (Willem Dafoe), a tough who mutters, "Fish ain't meant to be in a box."

Nor are they meant to be this gorgeous. Nemo, with its ravishing underwater fantasia, manages to trump the design glamour of earlier Pixar films. The dramatic set pieces — Marlin and Dory eluding jellyfish stings, Nemo's claustrophobic panic in a plastic bag — are realized with assured energy and balanced by a dozen deft comic performances, notably those of DeGeneres and Stanton himself as the lead sea turtle. Nemo has artistic and political resonances galore: it alludes to favorite movies, from Pinocchio to Psycho, and fearlessly takes on the powerful pet-shop and aquarium lobbies. There is also the secret insignia of any Pixar feature: a G-rated fart joke.

Nemo's fish-out-of-water plot was hatched back in 1992, when Stanton visited Marine World in Vallejo, Calif. His feelings of protectiveness toward his own boy Ben (now 10, and the brother of Audrey, 7) inspired the father-son story; a dentist's office fish tank, remembered from his childhood in Rockport, Mass., provided a second location for the drama.

Nemo's short fin — a deformity that does not slow him down one bit — became, says Stanton, "a metaphor for anything you worry is insufficient or hasn't formed yet in your child. Parents think their child's handicap is a reflection of the parent. They become obsessive and anxious over that, whether it is the child's ability to read or the way they walk. This movie says there is no perfect kid; there is no perfect father." And no guarantee that parents will ever have the answers. When Marlin asks the sea turtle Crush how a father knows when his kids are ready to swim out on their own, the wise old dude replies, "Well, you never really know. But when they know, you know — y' know?" Finding Nemo is about feeling one's way to knowing. It's about letting go and getting back.

To find out what their fish could and couldn't do, Stanton and his crew installed a fish tank and filled it with clown fish and blue tang, among others. Some became scuba divers to study their subjects more closely. They hired a "fabulous fish guy," Adam Summers, professor at the University of California at Irvine, who schooled them in the two types of swimming fish: rowers, who move their fins back and forth, and flappers, who move theirs up and down. By coincidence, Stanton had chosen one of each kind — a rower clown fish and a flapper blue tang — as his leads.

Any education is the process of learning how little you know. The Pixar animators had to learn a lot about what Stanton calls "the voodoo of underwater things. Things lose color when they go away from you and gain color when they come closer to you. There's crap in the water, and surge and swell." All this had to be analyzed or guessed at. "It was like somebody gave you a cake and said, 'O.K., figure out what ingredients it takes to make this,' but with no cookbook. And you're just going, 'I think I taste egg ... I think I taste sugar ...'"

Most actors who lend their voices to an animated feature can't even taste the eggs; they record their lines before the film is made and usually without other actors. So, even more than usual, the actor becomes a child, striving to please his coaxing, demanding father: the director. "There's so much info you're not privy to, and they've been living with this for years," says Dafoe, a grizzled delight as the fish-tank lifer who masterminds Nemo's escape from alkaline. "So you just have to give over and trust them." Or, as Brooks puts it, with a fatalism that is totally Marlin, totally Albert: "You hope it's going to work, and you think, If it doesn't work, I'd rather fail with them." For Brooks, there was one reason to take the role: "'Cause I have a 4 1/2-year-old boy and a 3-year-old girl. Period." If they like it, Dad's a hero.

In so many ways, behind the screen as well as on it, Nemo is a find-your-inner-grownup story. For a decade, Stanton was pleased to assist — as writer and co-director — the charismatic Lasseter, who created the first Pixar shorts and masterminded the art of CGI storytelling. "We all think John is the best thing since sliced bread," he avers, "and we'll follow his lead anywhere." But Stanton honed and hoarded his Nemo idea before pitching it to his Pixar pals. "Part of it was ego," he acknowledges. "Here I am making these movies with these four or five guys. After a while I didn't know what part of it was really me. For my own life journey, I wanted to know, What could I come up with if I only had me to bounce off of?"

Plenty of guys had their agile hands on the finished product. But Stanton — creator of the story, co-author of the screenplay, director and voice of its most endearing featured creature — is the true father of Finding Nemo. And what a beautifully bubbly child this child of Pixar has spawned.

• Richard Corliss