When frozen sandeel Ammodytes personatus which had been stored for a long time, was given to yellowtail for 70 to 80 days, some mortality of the rearing fish began to appear. The liver of the diseased fish showed some yellowish brown discoloration and histopathological study revealed that fatty degeneration of the liver cells was obvious, and this degeneration was especially heavy around bile-duct. The cell nuclei showed atrophy.