When you need a fast go-to meal at McDonald’s for lunch, you can count on Filet-O-Fish. An insider scoop – the fish they use on Filet-O-Fish is an Alaska Pollock. This fish is rich in Vitamin B-12 and in one serving, it can supply 61% of the body’s RDA for the vitamin. It also has a considerable amount of Potassium, Magnesium, Vitamin D and Vitamin B-6. The fish also has some Calcium, Iron and Vitamin A.