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May 9, 2014


United States

Louisiana—Antibiotics in Imported Shrimp


Veterinary drugs are commonly used to prevent and treat disease outbreaks on shrimp farms.  Several of these drugs are banned for use in shrimp farming in the United States.  They can be toxic to humans, with side effects that can be fatal.  There is also an increased risk of developing antibiotic resistant strains of human pathogens, including Bacillus and Vibrio species.  The Food and Drug Administration is responsible for the safety of all fish and fishery products entering the United States, but funding for testing is limited.  Examples of drugs with high enforcement priority include chloramphenicol, nitrofurans, fluoroquinolones and quinolones, malachite green and steroid hormones.  State testing has repeatedly resulted in the detection of banned drugs.  The objective of this study was to quantify veterinary drug residues in commercially available frozen shrimp.


Imported, farm-raised shrimp samples were purchased from local supermarkets and include shrimp from seven brands and six different countries.  A preliminary screening was done using rapid ELISA kits to test for chloramphenicol, malachite green, nitrofurans, and fluoroquinolones.  Samples tested positive for malachite green and fluoroquinolones; all samples tested negative for chloramphenicol and nitrofurans.  ELISA results were confirmed using liquid chromatography with tandem mass spectrometry.  Drug residues in shrimp samples were confirmed for chloramphenicol at concentrations ranging from 0.30 to 0.49 parts per billion, and enrofloxacin from 1.22 to 5.95 ppb. Results suggest that current testing by the FDA may not be adequately addressing imported seafood safety.  Concurrently analyzed wild-caught shrimp from the USA tested negative for all veterinary drugs considered.


Twenty-seven frozen samples of imported, farm-raised shrimp were obtained from five retail grocery stores in Baton Rouge, Louisiana. Samples included shrimp from Thailand, India, Indonesia, Vietnam, China, and Ecuador.  Fourteen frozen samples of domestic, wild-caught shrimp were obtained from six retail grocery stores in Baton Rouge, Louisiana.  Frozen samples were transported to the Department of Food Science at Louisiana State University Agricultural and Mechanical College in Baton Rouge, Louisiana and were stored at 80°C until further processing.


Detection and Confirmation of Drug Residues ELISA kits were used to rapidly screen shrimp samples to determine which drug residues were present. Chloramphenicol, fluoroquinolones, malachite green and nitrofurans were the drugs chosen for screening because of their ability to cause severe adverse effects in humans and their high enforcement priority status.


The results of this study confirm the presence of illegal veterinary drug residues in shrimp sold at the retail level in the United States.  Ninety-two percent of imported, farm-raised shrimp samples tested positive for at least one drug that is banned for use in food-producing animals in the United States.  Two of the four drugs considered in this study were detected using ELISA: fluoroquinolones and malachite green.  The fluoroquinolone enrofloxacin was confirmed in two out of five samples using LC-MS/MS.  Malachite green could not be detected using confirmatory methods.  Chloramphenicol was not detected using ELISA, but was detected in three out of five samples using LCMS/ MS.


Sources: Detection and Confirmation of Veterinary Drug Residues In Commercially Available Frozen Shrimp.  A Thesis Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in Partial Fulfillment of the Requirements for the Degree of Master of Science.  Jessica Danielle Johnson.  May 2014.  2. (a free, online newsletter about the feeds used in fish and shellfish farming).  Editor, Suzi Fraser Dominy (  Detection and Confirmation of Veterinary Drug Residues in Commercially Available Frozen Shrimp.  Issue 17, Volume 14, May 8, 2014.

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