“Occurrence of Kudoa sp. induced post-mortem myoliquefaction in Atlantic mackerel (Scomber scombrus) landed in Ireland (7080)”

Occurrence of Kudoa sp. induced post-mortem myoliquefaction in Atlantic mackerel (Scomber scombrus) landed in Ireland

Atlantic mackerel (Scomber scombrus) is Ireland’s most valuable wild-caught fish species. In recent years, Irish pelagic processors have noted an increase in the occurrence of post-mortem myoliquefaction, most commonly known as ‘soft flesh’ or ‘jelly flesh’. Studies from across the Northeast Atlantic on Atlantic mackerel have linked post-mortem myoliquefaction to a myxosporean parasite called Kudoa thyrsites, which is known to infect many freshwater and marine fish species. Despite mackerel’s economic importance, the number of incidents remain largely unknown in Ireland, and the causative agent has not previously been confirmed. Here, we examined Kudoa in Atlantic mackerel displaying post-mortem myoliquefaction and assessed the occurrence of ‘jelly flesh’. We confirmed the presence of K. thyrsites in the muscle tissue of affected mackerel collected from a major fishing port in the northwest of Ireland (Killybegs). Our K. thyrsites isolate matched the identity of previous isolates obtained from Atlantic mackerel in Scotland and Norway. During the 2024/2025 fishing season, the occurrence of ‘jelly flesh’ in commercial-sized mackerel was recorded as part of the quality control procedure at an Irish fish processing facility and was found to be low. Myoliquefaction was detected in only 0.5% of individuals (n=55/18610), with the majority of affected fish falling within the economically important size range of 300-500g. The findings build upon our understanding of K. thyrsites in Atlantic mackerel and highlight the need for long-term monitoring to elucidate sources of infection, routes of transmission, and temporal and spatial trends in the occurrence of the parasite. Ultimately, developing a robust comprehension of K. thyrsites infection is essential to assess its impact on the pelagic fishing industry in the wider Northeast Atlantic region.

1. Kiralyova, Viktoria, Marine and Freshwater Research Centre, Atlantic Technological University (ATU), Galway, Ireland, Presenter
2. Brophy, Deirdre, Marine and Freshwater Research Centre, Atlantic Technological University (ATU), Galway, Ireland, Author
3. O’Dwyer, Katie, Marine and Freshwater Research Centre, Atlantic Technological University (ATU), Galway, Ireland, Author
4. Talbot, Anita, Marine and Freshwater Research Centre, Atlantic Technological University (ATU), Galway, Ireland, Author
5. Gallagher, Michael, Bord Iascaigh Mhara (BIM), Killybegs Fisheries Harbour Centre, Killybegs, Ireland, Author
6. Giulietti, Lucilla, Institute of Marine Research (IMR), Nordnes, Bergen, Norway, Author