Seafood, which includes fish and shellfish, can be a great source of protein, iron and zinc which are crucial nutrients for your baby's growth and development. The omega-3 fatty acids in many fish, including DHA, also can promote your baby's brain development. But some types of seafood particularly large, predatory fish such as shark, swordfish, king mackerel and tilefish can contain high levels of mercury which are dangerous and should be avoided.