A study published in the International Journal of Epidemiology Wednesday found that children around 8 years of age, whose mothers ate four servings of nutrient rich fish a week, scored 16 percent higher on attention span testing, according to the Daily Mail. Oily fish like salmon and mackerel seemed to have the biggest effect when eaten during the first trimester of pregnancy, a time when most of the brain development takes place, according to Stanford Children's Health.