Fun idea xD I believe that improving the controls a bit would make it a good game to kill some time. Maybe moving with WASD, and using the LMB as a headbutt/kick? Perhaps that would give the player a bit more of control. I felt that just using the LMB was a bit unpredictable, it depended a bit much on luck for the fish to kick the rock and make it fly a few meters up.
But anyway, fun game, especially the motivational part of the voice-over xD