Mycotoxins in Aquaculture Feeds

Mycotoxins are toxic chemicals produced by certain species of molds usually belonging to the Aspergillus, Penicillium or Fusarium genera. The importance of mycotoxins to aquaculture and animal agriculture first became apparent during the early 1960s with outbreaks of aflatoxicosis in young turkeys in the United Kingdom and hatchery-reared rainbow trout (Onchorynchus mykiss) in the United States. In both cases the origin of aflatoxicosis was aflatoxin-contaminated feed (peanut meal for turkeys and cottonseed meal for trout). Other mycotoxins described since then include ochratoxin A, deoxynivalenol, T-2 toxin, zearalenone, moniliformin, cyclopiazonic acid and fumonisin. Aflatoxin is prevalent at certain times in corn grown in the southeastern U.S. and much research has been done on ways to mitigate its effects on corn crops and, subsequently, on animal agriculture. Plant breeders are seeking improved corn varieties that are more resistant to invasion by Aspergillus flavus, the mold that produces aflatoxin. The fungus is most problematic during hot, droughty summers, especially when developing corn kernels are damaged by insects. Aflatoxin contamination of corn can be reduced by planting resistant varieties, by irrigating to supplement rainfall, and by applying Bt (Bacillus thuringiensis) technology to control insects. Of course, failure to provide adequate storage facilities for corn and other feedstuffs can increase the levels of aflatoxin and other types of mycotoxin contamination in field crops infected with a toxigenic fungal organism. Cottonseed meal, commonly used in feed formulations for warm-water fish such as catfish, also can be contaminated with aflatoxins. Aflatoxins in feeds or feed ingredients are usually a mixture of four aflatoxins with only slightly different chemical structures. The most prevalent and most toxic to animals is AFB1. The other forms are AFB2, AFG1 and AFG2; they are included in the term “total aflatoxins.” The term “fumonisins” includes several mycotoxins that cause the same biochemical disruption of sphingolipid metabolism. FB1 is the most toxic and most prevalent, constituting about 75 percent of the total fumonisin mixture in contaminated corn. Some molds that can produce mycotoxins, such as certain Fusarium species, are more active during periods of prolonged moisture from excessive rainfall, as was experienced during the late summer and fall of 2009 over widespread areas of the southeastern and midwestern U.S.