I think the game is pretty nice considering it as your first game. The concept is great and I had fun playing it.
One thing that most first-time developers unnoticed is the difficulty (including me). I found it a little bit hard to shoot the fish, perhaps enlarging the targets or slowing it down a little bit will help. If you tested the difficulty and thought it's fine, you will probably have to lower it a little bit because you should be a pro at your game, and players like me are complete noobs haha.
Another thing is the feedback to the player on their gameplay. It will be good to have some cool yet not disturbing visual or audial effects when the player increases health to tell them they are doing a great job, and other effects to tell them to be more careful (like turning the screen red for a while). But that doesn't hugely affect the gameplay.
That's all, have fun developing!