“Nematodes in the liver of European flounder (Platichthys flesus) from the southern Baltic Sea (6852)”

Nematodes in the liver of European flounder (Platichthys flesus) from the southern Baltic Sea

Over the past decade, the presence of parasitic nematodes has been increasingly reported in numerous fish species across the Baltic Sea, with particular emphasis on the liver parasite Contracaecum spp. Anisakidae nematodes (such as Anisakis sp. and Contracaecum sp.) are zoonotic and pose a risk to human health. Surprisingly, the information related to the presence of these nematodes in European flounder (Platichthys flesus) is scarce, even though this flatfish is popular in human consumption. It is the third most commercially caught fish species in the Baltic Sea. The aims of our study were to 1) evaluate the level of European flounder infection with Anisakidae parasite in fish sampled in the Polish waters, southern Baltic Sea; and 2) compare the obtained results with available data. Liver samples were collected in February – March 2025 in two sampling areas located in the Polish marine waters: Gdańsk Basin and south of Bornholm Island. Visual inspection of 250 livers per area was conducted and revealed the presence of nematodes. Furthermore, subsamples of 50 livers per area were collected and digested in artificial gastric juice to reveal the presence of the nematodes. Identification of collected larvae was conducted based on anathomo-morphological features. Prevalence and intensity of infection were calculated and analysed in relation to the biological parameters of fish. In the Gdańsk Basin, the prevalence of nematode infection detected during visual inspection of livers was 0.8 %, and after digestion 8 % (intensity of infection 1-4); in the case of fish caught in the area south of Bornholm island these numbers were 2.8 % and 10 %, respectively, with the intensity of infection ranging 1-9. This indicates that using only visual inspection of livers leads to the underestimation of the infection rates. The presence of Anisakis sp., Contracaecum sp. and Hysterothylacium sp. in the liver of flounder was revealed. Our findings are consistent with previous research that has shown a rise in the prevalence of nematode parasites, including C. osculatum, among various fish species in the Baltic Sea over the past few years. Moreover, our results further support the idea that the increasing prevalence of Anisakidae nematodes may be linked to a rise in the abundance of grey seals, which serve as the final host in their life cycle.(The research is funded by a targeted grant from the Polish Ministry of Agriculture and Rural Development)

1. NADOLNA-AŁTYN, KATARZYNA, NATIONAL MARINE FISHERIES RESEARCH INSTITUTE, Presenter
2. PIWOSZ, KATARZYNA, NATIONAL MARINE FISHERIES RESEARCH INSTITUTE, Author
3. PAWLAK, JOANNA, NATIONAL MARINE FISHERIES RESEARCH INSTITUTE, Author