I like that you chose to use your game to get across an environmental message. However, I think that message could be better conveyed in the gameplay itself, and that the gameplay could be improved to make it more fun at the same time. It felt a little off that there wasn't any interplay between the fisherman side and the fish side while playing as the fish--no hooks in the water and no other fish. Also, it would be interesting if the fisherman's activity was more closely linked to the amount of trash/the dying fish during the gameplay itself, rather than just as a note at the end. Maybe as you upgrade, more trash shows up and the fish get scarcer?
I think you could make the catching minigame a whole lot harder, because the differences between the types of fish wasn't noticeable for me until the fourth level fish and I think I only lost one or two fish throughout the whole story mode. I also didn't see anything negative happen when hitting the trash.
I hope you keep making games and improving, because I can see that you're very creative and want to tell good stories!