Using salmon in 2 days, freezer or fridge?
It depends. Temperature works on a scale, the cooler it is, usually the less active bacteria will be.

With this in mind, my fridge has a special zone for meats and fish, very very close to zero degrees. The food won't freeze, but bacterial activity will be slowed enough that I would put it there a couple of days without worrying.

Freezing goes way beyond zero, usually - 13 to - 21 in some fridges, but it changes the quality of the product, specially if not vacuum sealed.

If your fridge has a special zone for meats like mine, I would use it. If not, freeze it just to be safe.