The sound design is really well balanced. I like that you used some nice calm ambient sound effect instead of music. The gameplay is simple but well executed and kept me entertained throughout. Having the time of the day change every time I fished something up is a real cool feature, not to mention that the ending is really cool too.
One issue I want to point out is that it becomes difficult to know if the bait is moving when there is nothing else in the screen. I would suggest having a steeper colour gradient from the top to the bottom of the sea so that the it is more obvious when the depth changes.
Great work!