Oscar is a fish who works at the Whale Wash for Mr. Sykes. He likes talking to the receptionist, Angie. Mr. Sykes was fired from the leader of the sharks Don Lino for joking about how Don Lino's son Lenny doesn't like to eat fish. Since Oscar didn't pay his dues, Sykes owes him 5,000 clams to pay for Don Lino's protection at the seahorse race track. Angie gave Oscar her grandmother's pink pearl so he can give the amount of money to Sykes.
Meanwhile, Don Lino is talking to his sons Frankie and Lenny. Frankie is an aggressive and carnivorous shark, while Lenny is an introvert and a vegetarian. Don Lino wanted Lenny to eat some shrimp, to which Lenny refused. He freed the shrimp out into the ocean. Don Lino told Lenny to be with Frankie to act like a shark.
At the racetrack, Oscar overheard two fish who wanted to bet on the seahorse Lucky Day. Oscar bet his 5,000 clams so that he could be a millionaire. A seductress named Lola got interested in Oscar for betting but admitted she's superficial. Oscar, Sykes, and the pufferfish's two jellyfish henchmen Ernie and Bernie watch the seahorse race. Suddenly, Lucky Day lost by tripping and Fish Fingers won the race. Oscar got sent to the deepest part of the ocean, where he is tortured by Ernie and Bernie.
Frankie and Lenny arrive where Oscar is and Lenny pretends to eat Oscar, freeing him. Outraged, Frankie chased towards Oscar until an anchor landed on his head. Lenny was so upset by his brother's loss and left the area. Ernie and Bernie saw Oscar next to Frankie's corpse and they asked him if he killed the shark. Oscar lied about it and became instantly famous.
Oscar enjoyed being known as a "Sharkslayer" and that all the fish of the Southside Reef looked up to him. The sharks learned about the "Sharkslayer" and Lenny swam towards the Southside Reef. Oscar encountered Lenny again and was scared that he would be caught with a shark. Upon discovering the lie and connecting it to the truth, Lenny figured out that Oscar lied. Lenny followed Oscar to a part of the Whale Wash where he cannot be seen. Lenny confessed to Oscar that he is a vegetarian and that his father was the head honcho of the great whites.
Later, Angie found Lenny and got frustrated with Oscar that he lied. Oscar had an idea where he would have a fake fight with Lenny.
Lenny pretended to be a carnivore as he was fake defeated by Oscar. This caught the attention of the other sharks. Oscar caught the attention of Lola, whose kiss was shown throughout the news, angering Angie. Angie admitted she loved Oscar before he lied and got famous.
Oscar, now ashamed of himself went back to his penthouse and talked to Lola. He turned down a relationship with her, which made Lola mad so she decides to beat him up. Oscar then decided to buy some gifts for Angie at the Whale Wash, where Lenny dressed up as a dolphin works there. Oscar received a call from Luca the Octopus and learned that Angie was taken by the sharks and there is a sit-down with all the sharks attending. Oscar told the truth to Sykes and realized that the sharks don't know that.
At the sit-down, Lola revealed herself as the arranger of the meeting and she wanted revenge against Oscar. Don Lino spotted Lenny wearing his disguise and removed the disguise. Don Lino accused Oscar of killing Frankie and converting Lenny into a dolphin.
Don Lino chased Oscar to the Whale Wash and got captured by the machinery. The crowd cheered until Oscar gave away the truth. He was Easily Forgiven by Don Lino and the others. Oscar became the new co-manager of the Whale Wash.
