Dietary Folic Acid and Bacterial Infections in Channel Catfish,Ictalurus punctatus

Channel catfish, Ictalurus punctatus, in a quadruplicate flowthrough aquaria for 15 weeks, were fed a semipurified basal diet containing no folic acid or with folic acid levels ranging from 0.2 to 10.0 mg/kg with or without antibiotic. A second study was conducted for 25 weeks under similar conditions but with semipurified diets containing either 20 or 200 mg/kg ascorbic acid and either 0, 0.4, or 4.O.mg/kg folic acid in a factorial design. Mortalities throughout both experiments were monitored and the etiological causes noted. Fish remaining from the second study were overwintered in circular tanks, kept on the same experimental diets, and challenged with Edwardsiella ictaluri after having been on experimental diets for 50 weeks. In both studies, the addition of folk acid to the basal experimental diet resulted in a decreased incidence of columnaris, Flexibacter columnaris. Folic acid concentration in the diet significantly affected mortalities in fish exmrimentallv challenged with E. ictaluri; however, there was significant interaction between the folic acid concentration and the concentration of ascorbic acid. At the lower concentration of ascorbic acid, 4 mg/kg of folic acid was required to reduce mortalities, but at the higher concentration of ascorbic acid, only 0.4 mg/kg folic acid was needed to reduce mortalities below that of the diet without folk acid. Antibody tilers were not affected by folic acid concentration at the lower concentration of ascorbic acid; however at the higher concentration of ascorbic acid, the diets containing 0.4 or 4 mg/kg of folic acid resulted in increased antibody production.