Sooner is better when it comes to cooking fish. When that's not possible, wrap fresh fish loosely in plastic wrap, store in the coldest part of the refrigerator, and use within 2 days. Cover and refrigerate any leftover cooked fish and use within 2 days.
If you purchase frozen fish, keep it in a freezer set at 0 degrees F or lower for up to 3 months. If you cut your own fillets or steaks, put them in self-sealing freezer bags or wrap in moisture- and vaporproof wrap before freezing.