Quality issues related to the presence of the fish parasitic nematode Hysterothylacium aduncum in export shipments of fresh Northeast Arctic cod (Gadus morhua)

The parasitic nematode Hysterothylacium aduncum commonly occurs in many fish species in the Northeast (NE) Atlantic. The parasite is considered non-pathogenic to humans. During spring and summer of 2018, lots of head-on eviscerated fresh NE Arctic cod (Gadus morhua) were shipped from Norway to Spain for commercialization. At arrival, the presence of lively roundworms (i.e. H. aduncum) in the transporting boxes was noticed. Consequently, fish lots were rejected causing substantial monetary losses to all involved parties. As part of the hazard assessment process, the epidemiology of H. aduncum in cod, NE Arctic saithe (Pollachius virens) and NE Arctic haddock (Melanogrammus aeglefinus) fished off West-Finnmark, Norway, was studied. Parasites were morphologically and molecularly identified to species level. Additionally, the viability of H. aduncum was assessed by simulating the conditions that prevail during transport of fresh cod to European market. The infection values of L4 larval stage or adult H. aduncum in the digestive tract of fish were highly variable, ranging from 100% prevalence with mean abundance (range) 238 (10-1092) in cod to 27% prevalence with mean abundance (range) 1 (0-22) in haddock. Fishing season was identified as most important explanatory factor for parasite abundance. Infection levels were higher during winter and early spring, and lower during late spring. Infection peaks of H. aduncum in the three fish species seemed to coincide with heavy predation on spawning capelin (Mallotus villosus) during winter and early spring. Thorough evisceration seems to remove most of the nematodes from the fish. However, parasites may remain hidden within the head cavities where they can stay alive and active under regular transport conditions for at least 14 days. Hysterothylacium aduncum can be completely removed from the product by evisceration, beheading and rinsing the fish prior to shipping. Alternatively, thorough cleaning or completely removal of the gills and pharynx may be considered.