Juli-Anne B. Royes
Department of Fisheries and Aquatic Sciences, University of Florida,
Aflatoxicosis in rainbow trout was a significant economic problem during
the 1960's after dry pelleted foods containing a high level of seed oil came into use. It was
described as a powerful carcinogen responsible for the widespread occurrence of hepatocarcinoma
in cultured trout. Aflatoxin is a mycotoxin produced by strains of the blue-green fungi
Asperigillus flavus. Aflatoxin B1 is a common contaminant of oilseed crops such as
cottonseed and groundnut meal, corn and to a lesser extent, wheat, sunflower and soybean.
Alfatoxin B1 is known as one of the most potent naturally occurring animal
carcinogens.1 Aflatoxin levels as low as 0.01ppb can induce neoplastic changes in
trout over a short period.
Aflatoxicosis is now rare in the rainbow trout industry due to strict
regulations enforced by the FDA for aflatoxin screening in oilseeds, corn and other feed
ingredients that are able to grow A. flavus. Because of their frequent occurrence,
especially in the Southeastern United States, agricultural commodities are routinely monitored
for the presence of aflatoxins. Although there are no official tolerance levels for mycotoxins,
the FDA allows a maximum of 20ppb in feeds or feed ingredients in interstate
commerce.1 However, in countries where there are no strict regulations, occurrences
of aflatoxicosis causing hepatic carcinomas have been on the rise especially in the Tilapia
industry. In tropical conditions this is a major problem because of difficulties in storage of
oil seeds under humid conditions. Temperature (> 80°F) and humidity (moisture levels
>14-15%) are two major environmental factors that promote the growth of the fungi.
Reported pathological changes generally include poor growth, anemia,
impaired blood clotting, damage to liver and other organs, decreased immune response and
increased mortality. Prolonged feeding of low concentrations of B1 cause liver tumors which may
appear as pale yellow, well-vascularized nodular lesions contrasting sharply with the reddish
brown color of normal tissue. A second type of tumor can be found that is grayish white,
translucent and smooth in appearance. These eventually become multinodular, large necrotic
tumors.2 In tilapia culture, the toxin is associated with renal tubular carcinoma,
lymphoma and hepatoma.3
1. Jacobsen, B. J., K. L. Bowen, R. A. Shelby, U. L. Diener, B. W.
Kemppainen, and J. Floyd. 1993. Mycotoxins and Mycotoxicosis. Alabama Cooperative Extension
System. Alabama University press Circular ANR-767.
2. Ashley, L. M. 1970. Pathology of fish fed aflatoxins and other
antimetabolites. In: A symposium on diseases of fishes and shellfishes. AFS special pub. No 5.
3. Haller R. D., and R. J. Roberts. 1980. Dual neoplasia in a
specimen of Saratherodon spilurus spilurus (Gunther) (Tilapia spilurus ) J. Fish
Dis. 3: 63-66.