PokerTracker

I'd like to know how to see the reg/fish ratio i've had on a specific day. For example, if i played 200 spins, how many of them were against 2 fish, how many against 2 regs and how many against 1 reg and 1 fish.

There isn't an automated method to calculate that kind of ratio but to see the players you've encountered on a given day you can use the 'Player Summary' report in the 'Results' section or you can go to 'My Reports' and create an 'All Players Report':

Guide: Creating My Reports