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.