Estonia's warming bodies of water catering to fish parasites
Although many parasites have always coexisted with fish in Estonia, encounters with heat-loving parasites in particular can pose a serious threat to populations of cold-water salmonids.
An expedition by Estonian University of Life Sciences researchers to Greenland and the Faroe Islands found that the parasite that causes a dangerous and currently incurable kidney disease in salmonids has spread much farther north than previously known. However, Anti Vasemägi, professor of fish genetics and genomics at the Estonian University of Life Sciences, said it is not known when the parasite, Tetracapsuloides bryosalmonae, reached the area. The parasite was first detected in Estonia nearly 30 years ago.
"But we still don't know, for example, when it reached Estonia. In Iceland, meanwhile, the parasite has spread rapidly over the past couple of decades, and this has also been linked to rising water temperatures," Vasemägi said.
Vasemägi noted that in Estonia, both warm-water fish and heat-loving parasites are currently thriving.
"When a cold-water fish encounters a parasite that prefers warmer water, it can end badly for the fish. In Estonia, this parasite causes the greatest mortality among juvenile trout, specifically in rivers where water temperatures have been altered by human activity. As we know, people have built many dams on rivers, straightened large sections of rivers and even cut down trees along riverbanks. All of this warms the water and raises its temperature," Vasemägi said.
According to Vasemägi, recent studies indicate that many parasites found farther south are reaching Estonia via migratory birds.
"For example, our new project funded by the Estonian Research Council will examine the spread of parasites associated with cormorants and a possible increase in their abundance in coastal waters."
The Estonian Federation of Fishing Clubs said there is nothing particularly unusual happening in Estonia. Vasemägi also noted that parasites are found in all fish species in Estonia and that fish generally cope well with them.
"It can be said that an extremely small proportion of our fish parasites can be dangerous to humans, and only if the fish has not been properly prepared. The rule of thumb is that people should avoid eating raw fish and fish roe, but fish that has been sufficiently heated or salted poses no danger to humans. So if fish is properly baked, boiled, salted or dried, there is no danger," Vasemägi said.
Vasemägi added that if anglers notice anything unusual about a fish, they can always send a photo to researchers at the Estonian University of Life Sciences and ask for advice.
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Editor: Marcus Turovski, Johanna Alvin
