Several people have reported that they have found dead pike with peeling skin and large, smelly blisters while fishing in Littoinen Lake recently. They said the fish were lying in a swampy area of the lake.
The lake has been featured in the news quite a lot this year, because it had been suffering from green algal blooms which depleted the oxygen in it. In May the local lake management organisation announced it was cleaning the eutrophic lake with a chemical treatment, and the Finnish Environment Institute SYKE declared the endeavour a success a couple of weeks later.
Anneli Weichmann, who is in charge of the cleansing project's follow up work, said she suspects the pikes' disfigurement was due to infection caused by fish lice.
Weichmann said that she is not aware of any fish kill in Littoinen Lake. If more dead pike are found, she said they will be sent to the Finnish Food Safety Authority Evira for examination.
Researcher: No way damage caused by fish lice
Tom Wiklund, a specialist researcher in aquatic pathology at Åbo Akademi University in Turku says fish lice are a very common parasite and not the cause of the damaged fish.
"There is no way that this could be caused by a fish lice infestation," Wiklund told Svenska Yle.
"Fish lice could certainly be found in these pike because the parasite is so common, but they do not cause this kind of damage," Wiklund said, adding that he could not give a definitive answer about how the fish were damaged without seeing them first.
"I would suspect that it is related to the chemical treatment which was carried out in the spring," he said.
"The pikes' heads are broken which causes problems for their balance in the water. [When] water balance is disturbed it kills the fish," Wiklund said.
EDIT 29.9.2017 This story has been edited to reflect the fact that Liittoisten Osakaskunnat, not the Environment Agency, initiated the chemical treatment of the lake.
EDIT 8.11.2018 This story has been edited to correct some misspellings of Littoinen.