Help! I'm a fish

Adventure about three children, Fly, Stella and Chuck, who set off on a fishing trip and end up in cranky professor Mac Krill's laboratory. The professor believes that the continents will soon become submerged, so he is working on a potion that will make it possible for humans to live under water. Fly's younger sister Stella accidentally drinks the potion and is transformed into a starfish and floats to the bottom of the sea. The two boys set off in pursuit of Stella, Fly in the form of a fish, and Chuck as a jellyfish. They have exactly 48 hours to find Fly's sister and the antidote, or else all three will remain fish for the rest of their lives. The story takes a dramatic turn when the pilot fish Joe, who has spent all his life as the underdog for a monster shark, obtains the antidote, a potion which also endows fish with human intelligence. Fly and Chuck have met with an enormous obstacle, but with their ingenuity and courage they might just succeed.