Help I'm a Fish

The three children Fly, Stella and Chuck set off on a fishing trip, but get into deep trouble when they wind up in cranky Professor Mac Krill's mysterious laboratory. The professor is working on a potion that will make it possible for humans to live under water, as he expects an impending submerging of the continents. Fly's little sister Stella accidentally drinks the potion, is transformed into a starfish and finds herself on the bottom of the sea. The two boys now have to follow after 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 they will remain fish forever. The three fish-children are hurled into amusing and thrilling adventures, and Stella gets a close girlfriend in the seahorse Sasha. The story meanwhile takes a dramatic turn when the pilot fish Joe, who has spent all his life as a "shark's toothbrush", gets his fins on the antidote... (official distributor synopsis)