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Dietary Folate Requirement Determined for Channel Catfish, Ictalurus punctatus^{1, 2, 3, 4,}

Department of Fisheries and Allied Aquacultures, Auburn University, Auburn, AL 36849 ^* Department of Nutrition Sciences, The University of Alabama at Birmingham, Birmingham, AL 35294

Juvenile channel catfish, Ictalurus punctatus, were fed semipurified basal diets containing 0, 0.2, 0.5, 1.0, 4.0 or 10.0 mg/kg of folic acid or 10 g/kg of succinylsulfathiazole 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 (0 folic acid), indicating that significant intestinal bacterial synthesis of folate occurs in channel catfish. There were positive quadratic regressions of weight gain, hematocrit, erythrocyte and leukocyte numbers, and positive linear regressions of plasma and liver folate on dietary folic acid concentrations. Broken-line analysis showed that the dietary requirements for folic 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 lymphocytes to erythrocytes were maximal in fish fed 4.0 mg folic 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 erythrocytes or "spectacle" cells.

KEY WORDS: • folate requirement • folate deficiency • folate • channel catfish

¹ Presented in part at the Annual Meeting of the World Aquaculture Society, June 16–20, 1991, San Juan, Puerto Rico [Duncan, P. L. & Lovell, R. T. (1991) The effect of folic acid on growth, survival, and hematology in the channel catfish, Ictalurus punctatus. 22nd Annual Conference and Exposition of the World Aquaculture Society (abs.)].

² Funded in part by F. Hoffman-La Roche, Inc., Basel, Switzerland and NIH grant CA-28103.

³ Alabama Agricultural Experiment Station Journal no. 8-933464.

⁴ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

⁵ To whom correspondence and reprint requests should be addressed: Department of Fisheries and Allied Aquacultures, 315 Swingle Hall, Auburn University, AL 36849.

Manuscript received 5 April 1993. Revision accepted 11 June 1993.