Very good idea, the inclusion of the different zones at different depths add a lot of, well, depth! I've always wanted to make something like this and this makes me want to start working on it. Good job! One thing to note is that the pixel sizes differ very much between the different sizes of fish, if you want pixel art to look consistent then you should not be scaling the sprite in engine, instead just make a bigger, more detailed sprite if you need it to be bigger. Other than that this is really good for a first individual game jam!
(Also try the game derrick and i made for 1 bit jam if you haven't :) )