Grasslamb

I'm fairly new to this game (and loving every second of it) so please bear with me here. If I want to see the new fish do I need to start clean on a new file since or will they eventually spawn in the lakes around my home? I'm guessing too that they might have a chance to appear in my unexplored areas on my map as well? The wiki doesn't explain much right now which is fine, but boy do I want to play Vintage Story Bass Fishing right now.