Your sentence describes a very unusual situation. It is possible that you bought fish yesterday. If so, we will eat it tomorrow. But if you bought fish two days ago or even just this morning, we will not eat it. There is obviously something very important about the date of purchase.
It would be more common to say : "If you have bought fish, we will have it tomorrow." Here, it doesn't matter when you bought the fish, only that you have done so.
I think that this is a mixed conditional though I am struggling to define it better.