Bloop looks cool! My idea is similar to yours but it is more like time pressure/stealthy puzzle kind of game. You start with big piranha looking fish which slowly loses its pigment and has to eat smaller fish to keep its color or it becomes black and dies. It also has to keep out of the bigger fish who also have a light and can see from a far rushing towards player and doing an instant kill :D You can hide under the seaweeds and wait for the fish to pass you... Here is a screenshot of the start of the first scene.
P.S. My pixel art sucks :D.