Ciguatoxins in marine water fish: Sophisticated testing strategy enables the detection of fish poisoning toxins

Poisoning by ciguatoxins after eating a seafood meal is still rare in Germany. However, ciguatera, as the disease is called, is one of the most common seafood poisonings worldwide of a non-bacterial origin. Against the background of an expansion in the global trade of seafood from the world’s oceans, an increase in future cases of ciguatera poisoning can be expected in Germany. Repeated ciguatera outbreaks in Germany since 2012 prompted the National Reference Laboratory for the Monitoring of Marine Biotoxins at the German Federal Institute for Risk Assessment (BfR) to break new ground in detecting ciguatoxins in fish, even when the fish’s origin is unknown. “Our testing strategy is based on two methods”, says scientist Dr. Dorina Bodi. “First, we use a highly sensitive cell-based assay test for screening, i.e., the rapid examination of even a larger number of samples of suspicious sea fish is possible. This test selectively detects the toxic effect of the target, ciguatoxins. If a sample is positive, the ciguatoxins are determined based on their chemical structure by a modern instrumental analysis in which liquid chromatography is coupled with mass spectrometry (LC-MS/MS).” The new testing strategy has not only been developed for testing fresh or frozen fish samples, but is also suitable for prepared (cooked) or dried fish. It has already proved its worth by solving a ciguatera outbreak case that occurred in 2017: Ciguatoxins were clearly detected in frozen raw fish from the same batch of fish.

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In a research project, BfR scientists, together with the authorities of the affected federal states, have clarified in detail, a ciguatera outbreak in Germany in 2017. The testing strategy proved that this outbreak was caused by two batches of mislabeled frozen fish caught in the western Pacific Ocean. Evidence of the presence of ciguatoxins was found by the US Food and Drug Administration (FDA) in meal remnants of prepared fish dishes consumed by people suffering from ciguatera. The BfR detected ciguatoxins in samples of unprocessed fish from one of the affected batches.

When tracing the batches along the commercial food chain, a comparison of the genetic material from the fish samples with the genetic material of fish species stored in a library (DNA barcoding) revealed that the fish species was Lutjanus bohar and not L. malabaricus as declared. It is known that the fish species L. bohar is capable of carrying ciguatoxins and causing ciguatera poisoning.

Ciguatoxins are produced by certain microalgae in tropical and subtropical waters of the world’s oceans. Certain fish species that feed on such algae absorb these harmful substances with their food and store them in internal organs and muscle flesh without these toxins negatively affecting the fish. Since ciguatoxins are highly toxic to mammals, i.e., humans, very small amounts, in the nanogram range, are sufficient to cause health disorders described as ciguatera.

The investigations of the 2017 ciguatera outbreak were conducted as part of a doctoral thesis at the National Reference Laboratory for Marine Biotoxins Monitoring in cooperation with the University of Naples Federico II, Italy. The findings regarding the causative fish species underline the importance of food authenticity, especially for food safety along global food chains.

As more and more fish species from warmer sea regions are exported to the EU, the investigation of ciguatoxins is of great importance for the clarification of poisoning cases. Ciguatoxin detection in combination with identification of the affected fish species can create awareness of ciguatoxin poisoning among the importer, institutions, and consumers. On this basis, appropriate measures can be initiated to avoid the import of sea fish species with a high risk of containing ciguatoxins. The testing strategy used by BfR in the study thus makes a decisive contribution to consumer protection.

About the BfR

The German Federal Institute for Risk Assessment (BfR) is a scientifically independent institution within the portfolio of the Federal Ministry of Food and Agriculture (BMEL) in Germany. It advises the Federal Government and the federal states (‘Länder’) on questions of food, chemical and product safety. The BfR conducts independent research on topics that are closely linked to its assessment tasks.

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