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Two invasive fish species found in southwest Finland

The Natural Resources Institute believes the potentially harmful fish were brought into the country illegally.

Katkerokalaa löytyi Suomesta
Bitterlings originate from the northern Black Sea. Image: Lauri Urho / LUKE
Yle News

Natural Resources Institute Finland (Luke) said on Thursday that two new non-native species of fish have been found in a pond in southwest Finland.

The Natural Resources Institute suspects that the fish were illegally brought into the country and released into the wild.

The species, which have never been reported in Finland before, are the common nase (Chondrostoma nasus) and the European bitterling (Rhodeus amarus). The fish were found during a population study of another alien species, the pumpkinseed (Lepomis gibbosus).

According to Luke, nases are found naturally in rivers of Central Europe. Bitterlings originate from the northern Black Sea but have spread northward and westward over a long period of time.

"Bitterlings were also found in Estonia in 2019. Their nearest common distribution area is now in Poland. It is likely that someone has brought the species in and released it into this pond in southwest Finland," Luke said on Thursday.

Luke researchers say it is not yet clear what kinds of impact the non-native fish may have on other species in the pond.

"Playing Russian roulette with Finland’s nature"

"Nases are known to carry a liver fluke, a parasite that can also affect humans, and can be transferred to other bodies of water through intermediate hosts such as birds. Bitterlings can carry diseases that can infect salmonids. Importing and stocking alien fish species without monitoring is like playing Russian roulette with Finland’s nature," said Lauri Urho, the Luke senior scientist who discovered the fish.

Luke points out that a permit is required to import live fish into Finland and to release them into waterways.

In the past 30 years, 10 new fish species have been found in Finland. Nine of them have been alien species that have come into the country’s waters through human activity.

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