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The Relationship of Hepatoma in Rainbow Trout to Aflatoxin Contamination and Cottonseed Meal¹

State of California Department of Public Health, Berkeley, California 94704

A test diet was formulated to approximate the commercial feed associated with the 1960 trout hepatoma epizootic in California. The same diet without the cottonseed meal portion served as the control. A third ration with food grade cottonseed flour substituted for the cottonseed meal was also tested. The trout on the 2 diets with the cottonseed products showed a high incidence of hepatoma. These results confirm previous observations associating the development of hepatoma in trout with the feeding of cottonseed meal. Chemical analyses relate the occurrence of hepatoma to aflatoxin B₁ in the cottonseed components of the test diets. These observations provide cumulative evidence that the hepatoma epizootic in California trout resulted from aflatoxin contamination of cottonseed meal ingredient.

Confirmation of the carcinogenicity of the cottonseed flour sample was obtained in a second experiment using a semipurified ration. Initial analysis of the cottonseed flour detected no aflatoxin. Subsequently an improved method detected 2 parts per billion of aflatoxin B₁; this is equivalent to 0.4 ppb in the experimental diet. Results from other studies indicate that the naturally occurring cyclopropene fatty acids and gossypol in the cottonseed components probably enhanced the carcinogenic action of the minute quantity of aflatoxin.

¹ This work was supported in part by USPHS Grants Nos. CA-05924, CA-06285 and ES00263.

² State of California, Department of Fish and Game, Sacramento, California 95819.

³ Department of Food Science and Technology, Oregon State University, Corvallis, Oregon 97331.

Received 10/23/67. Accepted 1/20/68.