Study on the etiopathogenesis of hepatoma in hatchery rainbow trout

Abstract

On the basis of the newest literature findings and of the results of observations recently made in Italian trouts hatcheries, the hepatoma occurring in rainbow trouts reared in hatcheries can be considered as a tumor chiefly elicited by alimentary factors; in fact its onset is connected to the use of special diets in the artificial feeding of these fishes. Two are the most commonly accepted nutritional theories: one is based on the probable existence of a carcinogenic substance included in commercial feed; the other postulates a degenerative action of imbalanced diets on hepatocytes, followed by regenerative-hyperplastic phenomena developing in a tumor. The present authors consider the latter theory as more reliable; in fact, following histologically the hepatoma development, a degeneration which is exclusive of rainbow trouts, that is « Liver Lipoid Degeneration », caused by an accumulation of ceroid in hepatocytes and histiocytes, was always observed. This could explain the receptivity of rainbow trouts to hepatoma and the fact that brown trouts and brook trouts reared in hatcheries never develope this tumor.