nutrient Requirements and Interactions Dietary Folate Requirement Determined for Channel Catfish, Ictalurus punctatus1-4

Juvenile channel catfish, Ictalurus punc- tatus, were fed semipurified basal diets containing 0, 0.2, 0.5, 1.0, 4.0 or 10.0 mg/kg of folie acid or 10 g/kg of succinyIsulfathiazole in aquaria for 15 wk. Fish fed the sulfonamide showed higher mortality, lower weight gain, lower thrombocyte counts, higher hemocytoblast and neutrophil counts, and lower liver folate concentrations than did control fish (O folie acid), indicating that sig nificant intestinal bacterial synthesis of folate occurs in channel catfish. There were positive quadratic regres sions of weight gain, hematocrit, erythrocyte and leu kocyte numbers, and positive linear regressions of plasma and liver folate on dietary folie acid concentra tions. Broken-line analysis showed that the dietary re quirements for folie acid for optimum weight gain, hematocrit, and erythrocyte and leukocyte numbers were 1.01, 1.17, 1.12 and 1.15 mg/kg, respectively. Plasma and liver concentrations of folate associated with normal growth and hematopoiesis were 22.9 nmol/L and 20.0 nmol/g, respectively. Ratios of leukocytes and lympho cytes to erythrocytes were maximal in fish fed 4.0 mg folie acid/kg, indicating that immunocompetence may increase as the dietary dose exceeds that required for normal growth. Anemia in folate-deficient channel catfish was characterized by pale livers, spleens, gills and kidneys, and by poikilocytosis, anisocytosis, pyknosis, cytoplasmic clearing, increased numbers of hemocytoblasts, macrocytosis, and binucleated erythro cytes or "spectacle" cells. J. Nutr. 123: 1888-1897, 1993.