Clams is a type of currency in Shark Tale (franchise). It is equivalent to dollars but in a seaworthy edition.
Sykes gave Oscar a loan of 5,000 clams and Oscar has to give it back to Sykes at the racetrack. Instead, Oscar decided to bet all 5,000 clams to Lucky Day which will pay a million clams for two hundred to one. Lucky Day lost the race and Fish Fingers won.