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Sealworm (Pseudoterranova decipiens) infection in grey seals (Halichoerus grypus), cod (Gadus morhua) and shorthorn sculpin (Myoxocephalus scorpius) in the Baltic Sea

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Abstract

The anisakid nematode Pseudoterranova decipiens, known as the sealworm or cod worm, can infect the flesh of several fish species. The parasite causes cosmetic problems for the fish industry and can cause abdominal discomfort if consumed by humans. There are only scattered studies on the abundance or distribution of the sealworm in fish and seals in the Baltic Sea. To remedy this situation, the extent of sealworm infection was investigated in cod (Gadus morhua) and shorthorn sculpin (Myoxocephalus scorpius) collected along the Swedish coast. A relative presence of the sealworm was also investigated in samples from grey seal (Halichoerus grypus) stomachs. Up to 100 % of the fish were infected in some of the areas. Sculpin were generally worse infected than cod, both in abundance and prevalence of parasites. General linear models showed a significant correlation between the number of seals in an area and the prevalence of sealworms in cod. There was a sharp decrease of infected fish in areas with salinity lower than 7 ‰. Even though the northern Baltic proper and the southern Bothnian Sea have a high number of grey seals, only one sealworm was found in a sculpin in that region, and none in cod. In grey seal stomachs the sealworm was only found in samples from the central Baltic proper; further north, all anisakid nematodes identified in seals were Contracaecum osculatum. The results indicate that seal presence drives the distribution in the southern parts of the Baltic and that low salinity, or some other variable which correlates with salinity, limits the distribution in the northern part.

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Acknowledgments

We thank Olle Karlsson (Swedish Museum of Natural History) for providing seal haul-out data, Karl Lundström for collecting nematodes from the seal stomachs and Massimiliano Cardinale for analytical support. Also, thanks to the people who assisted in collecting fish over the years, both university students and commercial fishermen. This study was financed by the Swedish Agency for Marine and Water Management, the Seals and Fisheries Program and Nybelins Fund. All work was carried out with approved applications submitted to the Ethical Board on Animal Experiments.

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Authors and Affiliations

  1. Department of Aquatic Resources, Swedish University of Agricultural Sciences, Turistgatan 5, SE-453 31, Lysekil, Sweden

    Sven-Gunnar Lunneryd & Maria Kristina Boström

  2. Bioforsk-Norwegian Institute for Agricultural and Environmental Research, Frederik A. Dahls vei 20, 1432 Ås, Norway

    Paul Eric Aspholm

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  1. Sven-Gunnar Lunneryd
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  2. Maria Kristina Boström
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  3. Paul Eric Aspholm
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Correspondence to Sven-Gunnar Lunneryd.

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Lunneryd, SG., Boström, M.K. & Aspholm, P.E. Sealworm (Pseudoterranova decipiens) infection in grey seals (Halichoerus grypus), cod (Gadus morhua) and shorthorn sculpin (Myoxocephalus scorpius) in the Baltic Sea. Parasitol Res 114, 257–264 (2015). https://doi.org/10.1007/s00436-014-4187-z

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