An observation on a high prevalence of hepatic carcinoma in hatchery-reared trout was made in the spring of 1960, triggered by government seizure of Idaho hatchery trout at the California border inspection station.1 Sporadic cases of hepatic carcinoma in trout have been described for at least 30 years, but within the past 10 years this disease has assumed epidemiological importance in the United States and Europe.2 The sudden awareness of trout hepatoma prompted the U.S. Bureau of Sport Fisheries and Wildlife to conduct surveys in practically all fish hatcheries in this country.
The epidemiological survey of state and federal hatcheries revealed the occurrence of disease in most trout-rearing areas of the United States. It was prevalent in healthy, fast-growing fish in advanced stages of growth, the highest rate being in those beyond 3 years of age.2 Rainbow trout were particularly affected, the prevalence in some hatchery populations
RAINBOW TROUT, HEPATOMA, AND DIET. JAMA. 1962;181(7):630. doi:10.1001/jama.1962.03050330060014