Tuna salad with potatoes and lettuce is a wonderful flavorous healthy salad. Tuna fish are of varying species and are found all over the world oceans. Researchers have recently discovered that tuna contains the mineral selenium in an unusual form called selenoneine. This form of selenium plays an important role in the health as an antioxidant. Because there are approximately two to three milligrams of selenoneine in a four ounce serving of tuna, we are likely to get some of this same antioxidant protection when we eat tuna.