Great game - is it inspired by "Feeding Frenzy" by any chance? :D Had lots of fun with this game (like I also had with Feeding Frenzy in the past).
The backgrounds of the first two levels were a little bit distracting, because it also had a lot of fish, making it hard to distinguish between "real" fish and background fish - this was especially the case for the first background. Sometimes I had the feeling that bigger fish spawned already inside of the map and not outside of it which resulted in an insta-death for me - I mean in the end it's my fault for staying too far at the border, but still.
The turning felt a little bit strange to me, maybe because of the pivot point where your tail just flips around. I never used the dash, because I felt that it didn't really increase my speed and thus didn't help me - you also could move really fast by just using the mouse, maybe some clamping would be good there.
The third level was pretty challenging, but had lots of fun beating it. It always feels so satisfying when you reach the biggest size and then can just gulp everything away.
EDIT: Oh, didn't talk about the audio. The music and also the sounds were also very great and fitting to the feel of the game.