Abnormal Folate Metabolism in Feed-Related Anemia of Cultured Channel Catfish

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Abstract
"No-blood disease" is a severe, feed-related anemia of channel catfish. Pathological features in advanced cases include almost total absence of circulating red blood cells, hepatic fatty change, megaloblastic arrest of hematopoiesis, and intussusceptions of the small intestine. In view of similarities to folate deficiency in man studies were made regarding the intake and metabolism of folic acid. When a bacterial culture medium, containing inorganic salts and folic acid as the sole carbon source, was inoculated with a small sample of anemia-producing feed, over 95% of the folate was destroyed. A yellow precipitate formed and had the characteristic uv spectrum of pteroic acid; it represented 32% of the folate originally present. Differential microbiological assays revealed that the same anemia-producing feed contained 20 times as much folate activity for Streptococcus faecalis as for Lactobacillus casei (59 .mu.g/g vs 2.6 .mu.g/g). The growth response is compatible with an excess of pteroic acid and/or formyl-pteroic acid which support the former but not the latter organism. Plasma folate activity (mean .+-. SD, ng/ml) assayed with L. casei and S. fecalis in 22 normal catfish (hematocrit range 32-43) was 17.2 .+-. 6.2 and 23.4 .+-. 13.8, respectively. Comparable values in 15 anemic catfish (hematocrit range 0 to 30) were 35.4 .+-. 33.7 and 58.7 .+-. 76.5. The mean plasma pteroate activity, estimated by subtraction, was 6.2 and 23.2 ng/ml, respectively, in normal and anemic fish. Fingerling catfish raised under controlled conditions on feed containing 130 mg/kg of pteroic acid failed to gain weight and developed anemia with the characteristic red cell morphologic features that are seen in the naturally occurring disease. We conclude that severe anemia in channel catfish can be caused by abnormal folate metabolism and may be due to ingestion of folic acid-breakdown products, such as pteroic acid. It is postulated that microorganisms in contaminated feed synthesize folate which, in turn, is converted to pterorate by a pseudomonad or similar organism.