Sprat (Sprattus sprattus) as a transmitter of Anisakid nematodes to piscivorous predators in the Baltic Sea

In the Baltic Sea ecosystem sprat (Sprattus sprattus) is a key fish speciesin the pelagic food web, both as predator on zooplankton and as prey of piscivorous consumers such as cod, salmon and marine mammals. However, sprat may not only be a source of nutrients, but also a transmitter of parasites. We assessed the presence of Anisakid nematodes in sprat from the western Baltic Sea. A total of 140 sprat individuals from Kiel Bight sampled in the first quarter of 2021 were visually inspected for the presence of nematodes during standard ichthyological analyses. Additionally, muscle tissue and all internal organs were digested in artificial gastric juice to reveal the presence of nematodes not detectable by visual inspection. Nematodes were identified based on the their anatomo-morphological features and using molecular analysis (ITS-1 rDNA). Three sprat individuals were infected with Anisakidae nematodes, each fish with one L3 larva. Contracaecum osculatum was found by visual inspection, while Anisakis simplex and Pseudoterranova decipiens were detected after digestion of muscle tissue. This is the first report of sprat infected with Anisakis simplex and Pseudoterranova decipiens in the western Baltic Sea and the first record of Anisakis simplex in Baltic sprat. Sprat is unable to get rid of these nematodes. Despite of the low level of infection with Anisakids, sprat may therefore play a role as transmitter of these nematode parasites to piscivorous predators in the Baltic Sea, considering the large number of sprat that these predators may consume over their life time. (Funding This work was supported by the European Maritime and Fisheries Fund and The Danish Fisheries Agency (33113-B-20-161)).