Sep 10, 2020 · Vitamins and Minerals. Rainbow trout is high in calcium, potassium, magnesium, and niacin. A 3-ounce serving of rainbow trout has 57mg of calcium, 409mg of potassium, 26.4mg of magnesium, and 4.58mg of niacin. It also has 52.7 IU of vitamin A, 3.78mg of vitamin B-12, and 645 IU of vitamin D.