Problem statement: In the early 1990s, the Parasitic Worms Division at the Natural History Museum (UK) had two almost identical enquiries concerning parasitic worms in the flesh of food fishes. One arrived in the diplomatic bag from the British Embassy in Quito, Ecuador, where fisheries authorities started getting reports of large cysts containing worms in the muscles and body-cavity of popularly eaten coastal fishes (groupers). As a precaution, sale of these fishes was temporarily stopped and existing catches condemned, with resulting economic hardships for fishermen. The second case concerned larval worms from the flesh of commercially important fishes (again groupers) in the Arabian Gulf. These were forwarded by the Scientific and Applied Research Centre of the University of Qatar, as the presence of these larvae in fish muscle had caused the price of some fishes in the Gulf to plummet, again causing considerable financial problems to local fishermen and fish-mongers.

Methods: The worms were first removed from fish tissue and processed (cleared) using standard procedures so that internal details of the worms could be seen under a microscope. Museum staff then used their taxonomic expertise to identify the group of worms responsible for the problems. Further research using the scientific literature resulted in more detailed identifications.

Outcomes and impacts: The worms were determined by Museum staff as larval tapeworms of the Order Trypanorhyncha, the adult forms of which tapeworms occur only in elasmobranch fishes (sharks and rays). The Museum was therefore able to assure the authorities in both countries that while these ‘wormy fish’ may be aesthetically unappealing, the worms found in the groupers were of no danger to human health. The worms comprised more than one species, which were subsequently identified and added to the Museum Collection. One possible reason for the sudden appearance of these worms in fishes off Qatar may have been a southwards movement of elasmobranchs due to pollution after the first gulf war.

Lessons: Taxonomic expertise is needed to determine both the identity of parasites and recognise stages in their life cycle. Such expert knowledge has a key role in ensuring the safety of fish consumption. Identification work by expert centres provides the opportunity to make scientifically important observations about species distributions.