According to the researchers the parasite Kudoa thyrsites is found in 0.8 % of Atlantic mackerel from the northern North Sea. It is said that enzymes released by the parasite gradually turn the fish flesh soft and jelly-like. Therefore, the condition is commonly known as “soft flesh”.
It is observed that parasite Kudoa is most abundant in large mackerel. Kudoa gives no visible symptoms in live mackerel, but 24-56 hours after catch, powerful enzymes released by the parasite gradually break down the fish’s musculature. This results in a soft and jelly-like fish filet, and therefore, the condition is commonly known as “soft flesh”. It is found that Kudoa-infections are neither treatable nor preventable. The proportion of mackerel developing “soft flesh” was low, and Kudoa was only detected in larger mackerel weighing more than 450 grams,” says Dr Arne Levsen, researcher at the National Institute of Nutrition and Seafood Research (NIFES) in Norway.
To investigate whether symptom-free mackerel also may carry the parasite, blood and muscle samples were taken from mackerel immediately after catch. There were no signs of infection, i.e. no Kudoa spores were present, in any of the samples. By using DNA-analysis, however, researchers from NIFES are currently investigating whether smaller mackerel may carry the parasite as well. It is well documented that Kudoa is present in Norwegian waters.
