This was done on just Javascript? Holy shit, it's near-perfect on almost every metric: it has a neat take on the theme, simple but nice puzzles, a pleasant artsyle and just a really good vibe overall.
My only nitpick is that it can be a bit confusing to control the fish underwater since its main shape doesn't rotate much, only the details (eyes and mouth). It would have been better if the game had traditional WASD/Arrow keys controls.