Really great stuff with lots of potential. Biggest issue right off the bat is the "move diorama" control being very weird. If the diorama is already centered and your cursor is in the center of the screen, then it works fine (although I'd either reverse the direction in which it draws or add an option to invert it). However, if you're offset from the center, or your cursor is offset, then it does a weird "snap" to a viewing position that's way off from how you had it.
In addition, it's unclear that you can only zoom in or zoom out while holding down the left mouse button. Even once I figured this out, the zooming is strange in that it begins as zoomed in as possible, and only allows you to zoom out, despite the fact that there's no reason to zoom out. The diorama is so small and there's so much empty space in the world already; it'd be cool if the zooming limits were adjusted so you could zoom in more.
Despite those control quirks, this is a very charming take on the idle genre, and this has tons of potential so long as more work goes into it. It might be a good idea to put in more detailed explanations of what some of the upgrades, since some aren't that obvious (fish population). I also learned from one of your comments that there's a "maximum limit on how much fish is available in the water to be caught" as well as a separate rate at which the wild fish replenish; perhaps that could be added somewhere in game where players can see those numbers and watch them change with their purchased upgrades.