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Rapid Toxin Testing for Shellfish in Florida

Why it is Important

The oyster and clam farming industries produce Florida’s top commercial seafood products, bringing in combined revenue of approximately $27 million each year. The Florida red tide species, Karenia brevis, which produces a suite of neurotoxins called brevetoxins, threatens these industries. During a bloom of K. brevis, filter-feeding shellfish take up the brevetoxins and hold them in their tissues, causing the shellfish to be toxic. If people eat contaminated shellfish, the brevetoxins can cause Neurotoxic Shellfish Poisoning (NSP). To protect public health, the Fish and Wildlife Research Institute’s Harmful Algal Bloom (HAB) group closely monitors the status of K. brevis on Florida’s coasts, providing technical support to the Florida Department of Agriculture and Consumer Services (FDACS), the agency that regulates approved shellfish harvesting areas.

During a red tide, FDACS closes shellfish beds to harvesting. Beds are only reopened after K. brevis concentrations return to normal and shellfish pass toxicity tests. The current method approved by the FDA to test K. brevis toxicity in shellfish only provides results for a small number of samples each week because it is time consuming and labor intensive; therefore, it can cause delays in reopening shellfish beds. Moreover, the method is outdated, non-specific, costly, and can result in false positives. These inefficiencies of the testing procedure worsen the already considerable economic losses during harvest closures. For example, $6 million was lost by the oyster industry during the 2002-2003 season.

Although K. brevis blooms cannot be prevented, it may be possible to minimize the economic harm they cause. Currently, researchers in the HAB group are working on a Florida Sea Grant-funded project to increase the efficiency of toxin monitoring and improve shellfish harvesting area management.

Project Goals and Approach

The primary goal of this project is to evaluate alternatives to the current regulatory test for NSP. One established method for toxicity testing holds particular promise for regulatory use. The ELISA (enzyme-linked immunosorbent assay) uses antibodies and a color change reaction to measure brevetoxins in a sample. Compared to the current method, the ELISA is quick, inexpensive and precise, allowing a large number of samples to be tested in a short period. Each of these advantages will minimize the amount of time that a harvest must remain closed and reduce the amount of money lost by the industry, while still upholding the safety of consumers.

The focus of the project is on the measurement of toxicity in three commercially and recreationally important species of shellfish: oysters, hard clams and sunray venus clams.

During the two-year study HAB scientists will:

  • Compare the accuracy, user-friendliness and costs of the ELISA with the current method
  • Conduct side-by-side analyses of actual regulatory samples to assess comparability
  • Share results with FDACS, shellfish farmers and scientists

Upon completion of the project, the results will be submitted to the Interstate Shellfish Sanitation Conference, the governing organization that establishes procedures for state shellfish programs, for consideration as an alternate tool for regulatory testing.

Expected Outcomes

The project will help the state transition to a more efficient and effective method for brevetoxin testing in shellfish, allowing more samples to be tested each week with more precise results, eliminating delays in reopening the harvest, and reducing economic losses by the industry.

If successful, on a local scale, an immediate benefit of the project will be expansion of a quarantine program implemented by FDACS, in which farmers harvest shellfish during a bloom and hold them until they are tested. If the test is normal, the farmers are allowed to sell the quarantined product. Currently, the program does reduce the duration that farmers cannot work, but regulatory testing is too time-consuming to help more than a few farmers each week. With the adoption of a quicker test, the HAB group will be able to aid nearly any farmer that requests to participate in the quarantine program.

Furthermore, researchers working on the project will gain a more thorough understanding of brevetoxin in the environment than was previously available. This knowledge will be spread throughout the scientific community leading to greater innovation and improvement in the field of shellfish regulation and toxin testing. The significance and applications of this project reach beyond Florida, as K. brevis is present throughout the entire Gulf of Mexico and threatens all U.S. and Mexican coastal communities. Validation of the rapid toxicity test for K. brevis will provide other regions the ability to successfully monitor blooms and reduce losses to their shellfish industries.