Coho salmon (Oncorhynchus kisutch) fed a diet deficient in folic acid for 24 weeks developed megaloblastic, normochromic macrocytic anemia. The anemia was further characterized by the presence of poikilocytic erythrocytes which were observed in stained preparations of peripheral blood. These abnormally shaped cells appear to be an important aid in the identification of folic acid deficiency. The anemia disappeared when the deficient fish were fed a recovery diet containing folic acid for 8 weeks.