. Nutritionally, it is far superior to meat, and has a delicate texture and flavor. However, tuna is a carnivorous fish and is enriched with higher levels of pollution, in which mercury levels are often excessive. It is recommended to eat it once every two weeks. Sardines and mackerel contain some elements that make up the nerve membranes, and those elements are closely related to the development of the optic nerve within the brain, which can help the fetus develop sound vision. If the fetus is deficient in this substance from 7-9 months of pregnancy to around the time of birth, symptoms such as neuritis and blurred vision can occur. It is best not to eat canned fish, fresh fish is not only flavorful, but also high in nutritional value.