Two attendees on the Natural History Museum field trip to Dorset were parasitologists, and they brought along some herring and a dogfish for us to dissect and look for parasites. Firstly we inspected ‘our’ fish for external parasites such as fish lice or leeches, but every fish was clean. Next we removed the gills and looked at them under a microscope to see if any parasites were attached. Again, none of the fish contained any parasites, leading to complaints of them ‘being too healthy”(!)
The next stage was to open up the body cavity and remove the organs to look for parasitic worms. I could immediately see that my herring was female, due to the large pair of roe, but at first could not see any parasites in the organs. After looking carefully I eventually found some small, white worms curled up into tight balls, which when removed with forceps into water started to uncurl and wiggle around. I eventually collected around 10 of the worms from the herring, quite a small number, so I was told. These nematode worms were probably the larvae of a nematode belonging to the genus Anisakis, a very common parasite in marine fish and mammals. It is harmless to humans when the fish has been frozen or cooked but can rarely cause an illness called anisakiasis when ingested with uncooked fish. The worms were preserved in alcohol to go of for genetic sequencing, hopefully we will later get some feedback on what they are identified as.