Severe oxidative stress is thought to be a principal cause of jaundice of yellowtail Seriola quinqueradiata

The jaundiced yellowtail Seriola quinqueradiata had yellow discolored skin and hyperbilirubinemia. Histology revealed that hemosiderin and ceroid occurred in the spleen. In the vascular system, there were vasculitis and sinusoidal dilatation. Hepatic cells showed degenerative figures with pyknotic or karyolytic nuclei, basophilic cytoplasm, cytoplasmic vacuoles in various sizes, and ceroidosis. In the bile duct system, however, there was no noticeable change. Hemoglobin contents of jaundiced fish were similar to those of control fish. Plasma taurine levels of jaundiced fish were significantly lower than those of control (p0.05). Judging from 2-thiobarbituric acid reactive substance values, in vivo lipid peroxidation progressed in the liver of jaundiced fish. In the plasma of jaundiced fish, contents of unconjugated bilirubin were significantly higher than those of conjugated bilirubin. A large amount of substance Xs, breakdown products of bilirubin scavenging active oxygen species, existed in the plasma of jaundiced fish. Therefore, jaundiced fish may suffer from severe oxidative stress, which might be a principal cause of jaundice. Liver superoxide dismutase and glutathione peroxidase activities of jaundiced yellowtail were significantly lower than those of controls.