"These fish are high in omega-3 fatty acids, vitamin D, vitamin B2, and other important nutrients like selenium and calcium," explained Davis, who noted that small fish are also less likely to be contaminated with mercury than their larger counterparts. Of those, vitamin D is especially crucial: it helps the body absorb calcium, which is key for strong bones, and it's found in very few foods. Try adding fish like sardines and mackerel to salads and pasta dishes.