Effects of alpha-tocopherol levels in extrusion pellets on in vivo lipid peroxidation levels and antioxidant activities in cultured yellowtail Seriola quinqueradiata injected with the causative bacteria of fish jaundice

Yellowtail Seriola quinqueradiata were fed on extrusion pellets supplemented with 12 (group I) or 88 (group II) mg/100 g of alpha -tocopherol ( alpha -Toc) for 46 days and then injected with the causative bacteria of fish jaundice. Changes in hematological values, bilirubin, alpha -Toc and ascorbic acid (ASA) contents and 2-thiobarbituric acid reactive substances (TBARS) values in the liver and plasma were analyzed. Growth rate and feeding efficiency were not significantly different between the groups. Seven days after infection, mortality was O and 40% in group I and II, respectively. The infection brought about hemolysis and jaundice in both fish. Judging from mortality and bilirubin contents in the plasma, jaundice was more serious in the fish of group II than in fish of group I. Considering prooxidant activity of alpha -Toc, this result might be caused by high alpha -Toc accumulation and low ascorbic acid contents in group II fish tissues.