Parasite diversity in haddock () from Icelandic waters.

Abstract

It is assumed that the biology and ecology of commercial fish species are relatively well-known, given that many of these parameters are key for stock assessment in fisheries management. Surprisingly (or not), several new parasite species are described annually from fish that are of commercial and cultural importance. Haddock () is an important commercial fish species in the North Atlantic with more than 50 parasite species having been reported from it. Despite its commercial importance in Icelandic waters, only 11 parasite species have been reported from Icelandic haddock. In February and March 2023, 26 haddock were sampled, including 16 and 10 from the north and south of Iceland, respectively. Fish were examined for parasites, with a focus on macroparasites (large, usually visible to the eye). Parasites were identified morphologically with identifications of helminths confirmed using DNA barcoding (Sanger sequencing). Overall, 19 different parasite species were recovered with 17 being shared between haddock sampled from the north and south of Iceland. Of these, eight represent new geographical records for parasites of haddock in Icelandic waters. Our study indicates that monitoring for parasites remains important, regardless of how well a species has been studied. Furthermore, reporting parasites per organ and per region, especially when areas are known to be influenced by different abiotic and physical features, is important in the context of parasites as biological tags for stock identification. Despite a small sample size, our study suggests that some parasites might act as potential biological tags for stock identification of haddock in Icelandic waters.