Rainbow Fish and the Storyteller by Marcus Pfister

The ninth book in the New York Times bestselling Rainbow Fish series. When Rainbow Fish meets a new friend, Humbert, he isn't sure what to think. Humbert tells all kinds of strange stories: Somewhere at the bottom of the ocean there's a plug! There's a blue whale living near here . . . and he's going to eat up all of our food. But before Rainbow Fish and his friends panic, they realize that Humbert just likes to make up tall tales. Rainbow Fish and his friends soon come up with an idea that might make them all happy-even Humbert.