PATHOPHYSIOLOGICAL STUDIES OF JAUNDICED Y ELLOWTAIL, SERIOLA-QUINQUERADIATA

Hematological and histological studies were carried out on yellowtail, Seriola quingueradiata, experimentally infected by intravenous inject ion of the bacterium causing jaundice of cultured yellowtail. Hematocr it values and blood hemoglobin concentrations of the experimentally in fected fish steadily decreased during 5 days after inoculation. In con trast, plasma hemoglobin and total bilirubin concentrations were maint ained at a normal level during 3 days, but rapidly increased on the fi fth day after inoculation. Histopathologically, the liver showed moder ate focal necrosis and destruction of the endothelium of veins in mori bund fish. The most extensive changes were observed in the spleen and kidney: severe anemia and necrosis in the splenic hematopoietic tissue , and degeneration and necrosis in the renal tubules and hematopoietic tissue were found. These pathological changes were similar to those o bserved in naturally infected fish. By indirect fluorescent antibody t echnique the bacteria causing jaundice were frequently detected in the spleen and kidney, but not in the hepatic parenchyma. These findings suggest that in jaundiced yellowtail destruction of red blood cells by the causative bacteria resulted in increases in serum hemoglobin and bilirubin concentrations.