The disease that affects the fish that becomes infected is called Proliferative Kidney Disease (PKD). In Norwegian: Parasitic kidney disease in salmonids. It is impossible to see with the naked eye, but already causes great damage. Both further south in Europe and in the USA. The tiny pest is not dangerous to humans, but affects different types of fish. It enters the fish through the gills, and lives primarily in the kidneys (blood bank) of the fish. There he inhibits the production of red blood cells, which in the worst case leads to fish death. In Norway, he has previously been detected in rivers all over the country, and targets, among other things, whitefish, char, aure and salmon. Discovery of the parasite in deep water in lakes is still completely new, something that causes great concern for the future of the fish species. Much is about rising temperatures. New places found Tone Jøran Oredalen is a university lecturer at the University of Southeast Norway (USN). She has recently delivered a doctoral thesis on the relevant fish parasite, and made disturbing discoveries after researching deep lakes in Telemark. Photo: Martin Torstveit / news – The parasite has previously been found in breeding facilities and rivers in Norway, but it has never been investigated in the deep, large lakes, says Oredalen. The parasite can potentially kill large numbers of fish in the future, as a result of a warmer climate, and the fact that young fish are particularly vulnerable. Only in Swiss rivers have fish died in large numbers, where it has been shown that the parasite has been a strong contributor. She has found several cases of the unpopular creature on fish in the five investigated Norwegian lakes. Not only in salmon, but also aure, char and whitefish. – There is no doubt that the parasite is there. Bigger challenge when the temperature rises The climate plays an important role in the spread. – The warmer the water gets, the greater the risk of the fish being hit. If you have between 12-14 degrees over a period of more than a fortnight, the risk of the disease developing is much greater, explains Oredalen. Norsjø is one of the places where the researcher has found parasites on the fish. Photo: Per Kåre Sandbakk/news aerial photo This is also the reason why she believes the fish are “safer” in terms of disease development at the bottom of large, deep lakes, where the temperature is usually significantly lower than on the surface. – Temperatures rise in the surface water in the summer, says the researcher. – But we expect the bottom water to remain cold in the future as well. The only question is how long. – The temperatures are rising. This is confirmed by the Norwegian Institute for Air Research, which says the water temperature has increased by three degrees in the last 30 years. – Frightened Among the fishermen on lake Norsjø in Telemark, the results of the research cause concern. – One gets a little scared to hear about this, says Erik Snippen. The angler is one of many who engage in so-called trolling, an advanced form of trolling. Erik Snippen spends much of his free time fishing in Norsjø. He is frightened by the new discoveries. Photo: Martin Torstveit / news He is familiar with the fact that it takes both time and a solid dose of patience to get fish on the hook. – It’s kind of a bit of fun, he says. If a parasite threatens the fish population where he runs his major leisure activity, the situation is quite different. – It’s good that they discovered him, but it’s also a bit scary. Now he and the others in the environment hope to be able to contribute to fighting the parasite if possible. – This is really nice water. There is a lot of nice salmon, aure and whitefish here. It would have been sad if it had severely exceeded the stock, says Snippen. Challenging to prevent the spread But is it possible to get rid of the parasite? Because even if the outlook for salmon is, despite everything, better in the large lakes with a lot of water than in rivers and shallower seas, you know that the temperatures rise steadily. – That is a good question, admits researcher Oredal. There is still hope, if one is willing to take the necessary steps. The parasite has not only been found on salmon, but also char (pictured), whitefish and aure. Photo: NINA Perhaps the most obvious thing is that you don’t look at fish that are already infected. Pollution also plays a role. – You can, for example, limit nutrients in the water to prevent pollution from stimulating the growth of so-called bryozoans, which are an important “host” for the parasite. Moss Moss Moss constitute a separate order in the animal kingdom. They are very small, often sessile and colony-forming animals. Most live in the sea, but there are also many species in freshwater. Fossil bryophytes have left numerous species as far back as the Ordovician, 500 million years ago. Source: Store norske lexikon – Another tool is our waterways. If you run with cold water in hot periods with little water in the summer, you will be able to reduce the chances of disease developing, she explains. – Conscious regulation of the temperature where we have the opportunity to do so can be a very good thing, believes the researcher. – Why is fish death so dangerous? – If you kill entire generations of young fish, then the whole group of fish will struggle afterwards. Especially if it happens often.
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Parasite affects salmon fish in Norwegian lakes – news Vestfold and Telemark – Local news, TV and radio
