Ascaridoid nematode infection in haddock (Melanogrammus aeglefmus) and whiting (Merlangius merlangus) in Northeast Atlantic waters

Haddock and whiting are two species of the family Gadidae that are exploited by fisheries mainly in European waters, the former being one of the most important seafood resources in Scotland (UK). The present study aimed to quantify prevalence, abundance and intensity of infection of the zoonotic parasite Anisakis spp. and other ascaridoid nematodes in these fish as part of a study on the risk to consumers. Fish were sourced from research trawling surveys during 2013-2015, aiming to cover a range of size-classes and different times of year. Samples were obtained from the North Sea, west coast of Scotland and the Barents Sea. Fish were stored frozen prior to separation of viscera and fillets and the use of pressing and UV visualisation to locate, identify and count Anisakis spp. and other ascaridoids in fillets (divided into 8 parts), liver and other viscera. A subsample of Anisakis spp. collected from haddock were identified genetically by means of two diagnostic markers (mtDNA cox2 and EF1 alpha - 1 nuclear DNA), and all were identified as A. simplex (s. s.). Both fish species showed moderate to high infection levels with Anisakis spp. (likely A. simplex (s. s.)) in the visceral organs and cavity, and rather low infection in the musculature. Those A. simplex (s. s.) larvae present in the musculature were mostly found in the anterior ventral area. hi both fish species, the infection rate increased with fish length and in haddock a negative relationship was observed between Anisakis spp. numbers in muscle and body condition. From our sampling of Anisakis spp. in fish muscle, in Scotland, whiting presents a greater human health risk than haddock in Scotland. The risk arising from consumption of haddock from the Barents Sea (with 72% prevalence of Anisakis) is markedly higher, although in all cases the risk of infection in humans can be minimised if fish are frozen or adequately cooked prior to consumption. We present previously unpublished information on reported cases of anisakiasis in the United Kingdom during 2000-2013, which included 4 cases from Scotland among 22 overall. While these findings suggest that anisakiasis is relatively rare in the UK, underreporting is likely and further investigation of the incidence of anisakiasis is needed.