Thank you very much for your responses and testing this.
I'm guessing your computer is quite a bit better than mine. The default number of regional tiles in the example project slowed mine down to 10-20 FPS, but reducing it to 8-12 regional tiles keeps my FPS high, so it's probably just a matter of me having an older computer. I may dive into the code eventually to see if there's a way I can simplify the fish pathfinding or something.