|Note from the SRAC Office: The following article appeared in the July, 2001 issue of the NWAC NEWS published by the Thad Cochran National Warmwater Aquaculture Center, Stoneville, Mississippi.|
SAFETY OF FARM-RAISED FISH
Craig S. Tucker and Sarah Harris
The last few years have been difficult for aquaculture public relations. Interest groups have made many irresponsible statements about aquaculture, ranging from claims of poor environmental stewardship to reports of widespread dioxin contamination in farm-raised salmon. In the first few months of this year, hardly a week passed without negative press coverage about seafood safety or environmental problems attributed to aquaculture. Then, to top things off, Federal and State Agencies issued advisories against eating certain fish because of metal or pesticide contamination.
The first advisory was issued in last winter by the United States Environmental Protection Agency and the Food and Drug Agency. The Federal advisory cautioned against eating certain fish because of mercury contamination. Then, in June of this year, the Mississippi Department of Environmental Quality issued an advisory against eating catfish and other species from Mississippi Delta lakes and steams.
Although the Federal and State advisories acknowledged that farm-raised fish are considered safe, that message is easily lost in the media frenzy that surrounds news on health-related issues. Contaminants such as mercury and pesticides are derived from the environment either directly from the water or from food items. Therefore, the level of contamination in fish depends on how much of the chemical is present in the environment. In that regard, controlled pond environments are clearly different than public waters, many of which receive discharges of industrial effluents of runoff from pesticide-contaminated fields. Logically, then, fish products from aquaculture should pose less risk to consumers than certain products from capture fisheries. Until recently, however, there was little scientific information to confirm or deny that conclusion.
Beginning in 1992, the Southern Regional Aquaculture Center (SRAC) funded a 3-year study to answer this question: Are aquaculture products produced in the southeast safe to eat. The answer was a resounding "Yes".
Twelve scientists from six states cooperated in this project which was entitled "Aquaculture Food Safety-Residues". They collected samples of channel catfish, rainbow trout, and crawfish from commercial farms throughout the region and carefully analyzed the samples for 34 pesticide residues.
Most of the pesticides were not detected in any of the samples and only one pesticide DDT was found in more than 10% of the samples. The finding that DDT and its breakdown products were the most prevalent pesticide residues is not surprising considering the extreme persistence of the chemical in the environment and its widespread use over three decades ending in the 1970s.
In the few samples where pesticide residues were detected, they were far below U.S. Food and Drug Administration "action limits." For example, the average concentration of DDT and its breakdown products in catfish was more than one hundred times lower than the FDA action limit for those compounds. Even the highest level of DDT found in catfish was still only 6% of the FDA action limit.
The same samples were also analyzed for nine "heavy metals" that are indicators of pollution and potential food safety problems. Most of the metals were found in only a small percentage of the samples and all were far below recommended safety limits. For example, the average residue of mercury in channel catfish was more than one hundred times lower than the FDA action limit.
One important finding, which was true across the spectrum of residues that were tested, was that farm-raised fish have lower residue levels than their wild-caught counterparts. The best example is mercury, which accounts for well over half of all fish consumption advisories issued by State and Federal agencies. The average mercury level in various wild-caught fish as reported in various other studies is 30 times greater than that found in channel catfish in the SRAC study. And, as a specific example that should be familiar to most people, the average concentration of mercury in canned tuna is 20 times higher than the average level in pond-raised channel catfish.
The finding that pond-raised channel catfish are amazingly "clean" with respect to potential environmental contaminants should not come as a surprise. Most chemical contaminants are associated with soils, and fish farmers avoid sites with a history of pesticide use. Even if the soil does contain low levels of pesticides, they are present only in the topmost layer of soil, which is removed and used to form levees during pond construction. Also, nearly all catfish ponds in Mississippi use pesticide-free groundwater to fill ponds, making it impossible to contaminate ponds with water-borne pollutants.
The growth and feeding habits of farm-raised catfish also minimizes the opportunity for accumulation of pesticide and metal residues, even if there are residues in the soil. Farm-raised catfish feed almost entirely on carefully prepared feeds rather than foraging on natural foods. This minimizes the possibility for "biomagnification" of pesticides through the food chain, as happens in natural settings.
The results of this study point to the need to differentiate the source of fish when discussing food safety issues because the risk of obtaining contaminated fish is much lower for farm-raised fish than for wild fish. If consumers are concerned about levels of pesticide and metal residues in seafood, farm-raised catfish, trout, and crayfish are healthy alternatives. 1
1The results of this study have been published in the following scientific articles:
Santerre, C. R., Ingram, R., Lewis, G. W., Davis, J. T., Lane, L. G., Grodner, R. M., Wei, C. I., Bush, D. H., Shelton, J., Alley, E. G., and Hinshaw, J. M. 2000. Organochlorines, organophosphates, and pyrethroids in channel catfish, rainbow trout and red swamp crayfish from aquaculture facilities. Journal of Food Science, Vol. 65, No. 2, pages 231-235.
Santerre, C. R., Bush, P. B., Xu, D. H., Lewis, G. W., Davis, J. T., Grodner, R. M., Ingram, R., Wei, C. I., and Hinshaw, J. M. 2001. Metal residues in farm-raised channel catfish, rainbow trout and red swamp crayfish from the southern U. S. Journal of Food Science, Vol. 66, No. 2, pages 270-273.
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