I really enjoyed this game, despite probably not playing this in the intended way. I get this feeling that this was never really tested with max mouse DPI (I could circle the entire map just by drawing a 1-inch diameter circle with my mouse) so it was a bit of a learning curve not to get immediately eaten by bigger fish. Eventually I got good at dodging between fish, enough that I never really used the dash, since just doing it with the mouse meant more control. I assume that the presence of the left-click to dodge mechanic means that doing precision dodges with the mouse is unintended. I did actually use the dash a few times though and it was fun. The other explicitly stated mechanic, right-click to inhale, felt kind of weak enough that it was the main cause of my death (due to the length of the animation and the vulnerability of the player character during this animation) until I stopped trying to use it. I'd also suggest having a toggle for cursor visibility during gameplay because I had no idea what direction I was going at first.

As for the music, it's very well composed. My only nitpick with it is that there's nothing particular about it that says "this is music from a fish-related game" to me, only that it is good arcade game music (side note, you forgot to import as loop). I noticed that the main theming of the game is tropical reefs- there's tropical reef backgrounds, it's a bunch of islands, there's tropical fish. It'd be nice if the composer had used instruments like steel drums, the xylophone, or certain synths typically associated with island levels or water levels to invoke that kind of "oh, this is a water level" feel. I personally (when I'm not scrambling to compose something) like to listen to compilations of music related to the theme before deciding what and how to compose something, with the goal of gaining some inspiration as well as getting an idea of the overall feel of what components contribute to this feel, such as what instruments are used, the level of complexity, the type of scale (major, minor, pentatonic, etc.), and the time signature. Of course, the goal isn't to just take all the best parts of those songs, but to understand what works, and either building upon that or subverting expectations for a unique twist.

Last note. The bonus room was kinda funny. Reminds me of oxygen bars.