DIETARY-FOLATE REQUIREMENT DETERMINED FOR CHANNEL CATFISH, ICTALURUS-PUNCTATUS

Juvenile channel catfish, Ictalurus punctatus, were fed semipurified b asal diets containing 0, 0.2, 0.5, 1.0, 4.0 or 10.0 mg/kg of folic aci d or 10 g/kg of succinylsulfathiazole in aquaria for 15 wk. Fish fed t he sulfonamide showed higher mortality, lower weight gain, lower throm bocyte counts, higher hemocytoblast and neutrophil counts, and lower l iver folate concentrations than did control fish (0 folic acid), indic ating that significant intestinal bacterial synthesis of folate occurs in channel catfish. There were positive quadratic regressions of weig ht gain, hematocrit, erythrocyte and leukocyte numbers, and positive l inear regressions of plasma and liver folate on dietary folic acid con centrations. Broken-line analysis showed that the dietary requirements for folic acid for optimum weight gain, hematocrit, and erythrocyte a nd leukocyte numbers were 1.01, 1.17, 1.12 and 1.15 mg/kg, respectivel y. Plasma and liver concentrations of folate associated with normal gr owth 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 in crease as the dietary dose exceeds that required for normal growth. An emia in folate-deficient channel catfish was characterized by pale liv ers, spleens, gills and kidneys, and by poikilocytosis, anisocytosis, pyknosis, cytoplasmic clearing, increased numbers of hemocytoblasts, m acrocytosis, and binucleated erythrocytes or ''spectacle'' cells.