I really like the concept of switching up which fish you can eat!
I do wish that the fish shapes were a bit more different - some longer, some with more fins, etc. Yes, they're different sizes, but the edible indicator doesn't show size - so the only thing you can judge by are the colors.
I also think it could be fun if the game changed in difficulty as you went along - for instance, if there were only two possible fish to eat at the start of the game. Like, in my first run, a fishing boat drove by in the first few seconds, and I had no clue what was going on. Adding in a difficulty curve could go a long way to making the game feel more polished!