I'm very curious to see if these will produce tubers on the roots!

There are a number of ways for nutrients to get into the water, the fish waste alone adds quite a bit. I don't think potatoes actually use a lot of nutrients for this kind of growth, but I'm not really sure. I do know that when growing them in standard medium, the roots need to be dark to create tubers, but those rules may change with the roots in water like this; in standard medium, those roots would start growing leaves.

I hope you keep us updated, welcome to the community!