Estonian researchers discover a dangerous fish parasite in Greenland and the Faroe Islands

As the climate warms, it could become a serious threat to salmonid populations that have so far remained in good condition.

In two studies published in Polar Biology and the Journal of Fish Diseases, an international research team led by scientists from the Estonian University of Life Sciences and the Swedish University of Agricultural Sciences investigated the distribution of the salmonid parasite Tetracapsuloides bryosalmonae in rivers across Greenland and the Faroe Islands for the first time. This microscopic myxozoan parasite causes a temperature-dependent proliferative kidney disease (PKD) in many salmonid species, including Atlantic salmon, brown trout, rainbow trout, grayling and Arctic char. 

PKD primarily affects juvenile fish and the disease outbreaks typically occur when water temperatures remain above 15 °C for extended periods, causing kidney damage, anaemia and often high mortality.  In several Central European countries, proliferative kidney disease has been linked to significant declines in salmonid populations, particularly brown trout. Researchers estimate that continued climate warming could increase the risk of disease outbreaks even in cold-water rivers where salmonid populations have so far remained healthy. 

The findings surprised the researchers. Of the sixteen streams examined in the Faroe Islands, the parasite was absent in only two, while in the remaining streams most of the fish were infected.

"Although the Faroe Islands are one of Europe's most isolated archipelagos, the parasite turned out to be surprisingly widespread. We had previously found this pathogen in Northern Norway, but we did not expect such an extensive distribution in the Faroe Islands," said Magnus Lauringson, a research fellow at the Estonian University of Life Sciences.

The results from Greenland were equally surprising. In the Nuuk fjord region (locally known as Nuup Kangerlua), the parasite was detected in four of the six rivers surveyed. Particularly remarkable was its discovery in Greenland's only Atlantic salmon population, where all salmon examined were infected, along with nearly two-thirds of the Arctic char.

"The Greenland findings significantly expand our knowledge of the distribution of Tetracapsuloides bryosalmonae. Until now, there had been no evidence that the parasite could persist under such extreme Arctic conditions," Lauringson said.

DNA analysis showed that the parasites found in Greenland and the Faroe Islands are genetically almost identical to those found in Europe.

"Although Greenland is geographically much closer to North America, the genetic similarity of the parasite suggests a possible European origin," explained Lilian Pukk, a research fellow at the Estonian University of Life Sciences who led the study.

"Our expedition has helped place the distribution of Tetracapsuloides bryosalmonae into the broader context of climate change. Since temperature affects the distribution and life cycle of many pathogens, it is important to understand how northern populations may respond to changing environmental conditions," Lauringson added. He also added that T. bryosalmonae is not zoonotic and does not infect humans, meaning that infected fish are completely safe to consume.

The studies received funding from the European Union's INTERACT III programme (Horizon 2020 Grant Agreement No. 871120) and the Estonian Research Council (PSG849 and PRG3078). Field equipment for the expedition was provided by Vision Fly Fishing.

Publications

1. Lauringson, M., L. Pukk, L. J. Hansen ja A. Vasemägi. 2026. "First Report of the Malacosporean Parasite Tetracapsuloides bryosalmonae in the Faroe Islands Reveals Widespread Distribution and High Prevalence in Brown Trout." Journal of Fish Diseases 49(7): e70134. https://doi.org/10.1111/jfd.70134link opens in new page.
2. Lauringson, M., L. Pukk, K. Raundrup jt. "First report of the proliferative kidney disease (PKD) agent, Tetracapsuloides bryosalmonae, in freshwater salmonids of Greenland." Polar Biology 49, 86 (2026). https://doi.org/10.1007/s00300-026-03515-9link opens in new page.