Warming waters help fish parasites spread north

Warming waters are creating favorable conditions for fish parasites, including one that causes a dangerous and currently incurable kidney disease in salmonids, ERR reported, citing Vikerraadio.

An expedition by researchers from the Estonian University of Life Sciences to Greenland and the Faroe Islands found that the salmon kidney spore parasite is distributed much farther north than previously known. Researchers do not know when it reached those areas. The parasite was first found in Estonia nearly 30 years ago.

Anti Vasemägi, a professor of fish genetics and genomics at the Estonian University of Life Sciences, said the parasite has spread rapidly in Iceland over the past two decades, a development associated with rising water temperatures.

“When a cold-loving fish encounters a parasite that prefers warmer water, it can end badly for the fish,” Vasemägi said.

In Estonia, the salmon kidney spore parasite causes the highest levels of mortality among young trout in rivers where human activity has altered water temperatures. Dams, straightened river channels and the removal of trees from riverbanks all contribute to warmer water, he said.

Many parasites found farther south are reaching Estonia with migratory birds, according to recent research. A new project funded by the Estonian Research Council will study the spread of parasites associated with cormorants and a possible increase in their numbers in coastal waters.

The Estonian union of fishing clubs said there was nothing exceptional about the situation. Vasemägi also noted that all fish carry parasites and usually cope with them well.

Only a very small proportion of fish parasites may pose a risk to people, and only when fish have not been properly processed. Raw fish and roe should therefore be avoided, while fish that has been sufficiently cooked, boiled, salted or dried does not pose a danger, Vasemägi said.

People who notice anything unusual in a fish can send a photograph to researchers at the Estonian University of Life Sciences and ask for advice.