How quickly does cod go bad if you put it in the refrigerator?

I bought some cod over the weekend in Chinatown - I was going to buy it in the East Village, but the idea of spending $9.99 / lb. didn't really appeal to me. So Chinatown it was. I bought it a fish market on Mott St, live frogs in trash barrel included. Gross. I know, I have eaten frog, in fact, I love this dish at Nha Trang-- frog legs in chili lemongrass sauce, but seeing the real live suckers at the market just grossed me out.

So I haven't had time to marinate the cod; I'm following a recipe out of Nobu's cookbook for black miso cod. I bought the cod on a day when most liquor stores are closed (hmm, is this a bad sign for the quality of the cod?) so I just stuffed it in the freezer. On Monday I bought the sake I needed, but since the cod was frozen and I needed to defrost, I left it. Now its Friday, I defrosted the cod finally yesterday when I remember to take it out of the freezer before leaving for work.

Again, last night after I got home from work at 11:00 PM, I decided to hold off on preparing the marinade. So now the cod is almost a week old and when I finally do marinate it, its supposed to marinate for 3 days! Maybe I should start over with a new cod?

Shit.