Your pitch made me imagine "hold button to go up, release to go down" sidescroller and game itself looks way more interesting than that! I'd rather use the line you have in game page - "Guppy is a 2D watercolor fish simulation". It's already pretty interesting!
Thanks. :) Usually I do use the simulation line, though "swim like a fish" is the shortest.... but you're right, absent other information it's easy to think of the familiar with the short version.
