Plot
An underachieving bluestreak cleaner wrasse named Oscar (Will Smith) is fantasized about being rich and famous while making his way to work by following in his dad's footsteps as a tongue scrubber at the local Whale Wash. Soon after arriving he is called to the office of his boss, a puffer fish named Sykes (Martin Scorsese), to discuss the fact that he owes "five thousand clams" and has to pay it back by the next day. After explaining this to his best friend Angie who is an angelfish (Renée Zellweger), she offers him a chance to pay back the money by pawning a pink pearl that was a gift from her Grandmother. Oscar brings the money to the race track to meet Sykes, but becomes distracted by his wishes of grandeur and, upon hearing that the race is rigged, places it all on a long-shot bet by the name of "Lucky Day". Such a million dollar bet is noticed nearby by a beautiful lionfish named Lola (Angelina Jolie), who flagrantly seduces an excited Oscar, but Oscar is very disappointed when she leaves once Sykes tells her he is a whale washer. Sykes is furious that Oscar bet the money but nonetheless agrees to see how the race turns out. Moments before their "horse", "Lucky Day" crosses the finish line he trips and falls on line. The race is lost and Oscar is set to be punished in a secluded area for his impulsiveness.

Meanwhile, on another side of the ocean, in the wreck of the RMS Titanic, a family of criminally-inclined Great white Sharks has a problem with one of their sons, Lenny (Jack Black) (who is a Vegetarian) . Lenny refuses to act the part of a killer and wishes to not have to live up to those expectations. Finally his father, Don Lino (Robert De Niro) loses patience and orders Lenny's more savage big brother Frankie (Michael Imperioli) to show Lenny the ropes. As the two sharks set out to go in accordance with their father's wishes, Frankie spots the scene where Oscar is being electrocuted by Ernie and Bernie (Doug E. Doug & Ziggy Marley), Sykes' two Jamaican Physalia physalis thugs, and sends Lenny off to attack. The jellyfish spot Lenny and swim off, leaving Oscar alone with him. Lenny frees Oscar but fails to trick Frankie, who becomes annoyed and charges at Oscar when an anchor falls and kills him. Lenny flees, overcome with grief and guilt. As no one saw the deed done and Oscar was seen near the body, everyone thinks he did it, and Oscar sees this as the chance to both redeem himself and receive his fame.

Oscar comes back to the city with a new title of the Sharkslayer. Sykes becomes his manager, Lola becomes his girlfriend, and Oscar moves to the "top of the reef" to live in luxury. At the same time, Don Lino has everyone out looking for Lenny, and when several get close to Oscar's town the other fish expect him to drive them away. On the way he meets Lenny once more who forces Oscar to let him stay with him because he does not want to go home. Soon Angie finds out about the lie and threatens to tell everyone but Oscar and Lenny convince her to keep quiet. Although Oscar desires to please everyone, he soon discovers that he pleases no one; his paramour Angie is heartbroken by the fact that Oscar is no longer honest, while her hedonistic rival Lola repeatedly reminds Oscar that he has her only as long as he is famous. With Don Lino planning revenge, Oscar and Lenny stage an event where Lenny pretends to terrorize the town and Oscar must defeat him, throwing him into the depths of the ocean. Though this further cements Oscar as the Sharkslayer, it greatly angers Don Lino. Oscar leaves Lola for Angie after Angie reveals that she had feelings for Oscar even before he became famous, but this leaves Lola determined to get revenge.

Oscar buys some Valentine's Day gifts for Angie, but before he can present them to her, he finds that Don Lino has kidnapped Angie in order to force a sit-down. Lenny comes along, now disguised as a dolphin named Sebastian. They arrive at the meeting to find Lola next to Don Lino, while Angie is bound and gagged with duct tape and presented to Don Lino on a plate, who prepares to eat her if Oscar doesn't comply. Oscar just laughs and Lenny as "Sebastian" lunges forward to scoop Angie into his mouth, freeing her from Don Lino and giving Oscar dominance over the sharks. However, he spends too much time threatening the sharks and doesn't realize how much pain Lenny is in, and Angie is regurgitated onto the table. Don Lino suddenly realizes it's Lenny and proceeds to chase Oscar through the reef, but Oscar heads for the whale wash and ends up trapping both sharks. Given an ovation by the other fish, Oscar finally has enough and confesses that he is not a "Sharkslayer" and that it was the anchor that had killed Frankie. He then stated to Don Lino that everyone likes Lenny for the way he is, strongly urging him not to prejudge people before he knows them properly and to not make the mistake he made in prejudging his wealth. Realizing that Oscar is right, Don Lino apologizes to Lenny and reconciles with him while making peace with Oscar, stating that he and his gang bear him no ill will. Oscar forsakes all the wealth he has acquired, makes peace with the sharks, becomes manager of the Whale Wash (now frequented by sharks), and starts dating Angie and starts to have a happy, honest life.

In the post-credits scene, Lola comes to see Oscar in the top of the reef, wanting to make amends with him for what she did, but all she finds is a hermit named Crazy Joe waiting for her.

Critical reception
The film holds a 36% "rotten" rating at the review aggregate website Rotten Tomatoes, with the consensus: "Derivative and full of pop culture in-jokes." On another review aggregator, Metacritic, the film holds an 48 out of 100 rating or "mixed or average reviews."

John Mancini, the founder of the Italic Institute of America, protested Shark Tale for perpetuating negative stereotypes of Italian-Americans.

The American Family Association, a Christian conservative organization, raised concerns about Shark Tale, suggesting that it was designed to promote the acceptance of gay rights by children.

Roger Ebert gave Shark Tale two out of four stars, observing, "Since the target audience for Shark Tale is presumably kids and younger teenagers, how many of them have seen the R-rated "Godfather" and will get all the inside jokes? Not a few, I suppose, and some of its characters and dialogue have passed into common knowledge. But it's strange that a kid-oriented film would be based on parody of a 1972 gangster movie for adults." He also opined that younger viewers would have trouble enjoying a film about adult characters with adult problems, such as an elaborate love triangle and a main character wanting to clear his debt with loan sharks, and compared it to more successful fish-focused animated features like Pixar's Finding Nemo, which Ebert felt featured a simpler plot that audiences could more easily identify with.

However, Richard Roeper commented that although the film wasn't on the same level as Finding Nemo, it was definitely a film worth seeing.