An unwelcome guest in our waters

A new species of fish – Amur sleeper or Perccottus glenii – has appeared in Estonian waters. The first known finding was made in June this year when ichthyologists caught two individuals in the course of test fishing in the area of Narva reservoir.

The appearance of alien species should always be treated with care. If the alien species are more viable than local species, the guests may oust the local species from their habitats. As far as we know, Perccottus glenii is a fish species likely to change natural water ecosystems considerably in the new areas where it has spread.

The precondition for this is the extraordinary adaptability of the Perccottus glenii. The fish tolerates pollution, the lack of oxygen, and freezing and drying of water bodies exceptionally well. Its diet consists of invertebrates, small fish as well as amphibian larvae.

The status of a species with such a great adaptability and potential to change its new living environment needs to be closely monitored.  The range of the Perccottus glenii in Estonia has to be restricted. First of all, we should start by observing the spreading tendency and informing the public about the problems related to this invasive species.

The appearance of the Perccottus glenii resembles our gobies living in the sea – the fish has two back fins; chest and ventral fins are located more or less side by side close to the head; the brownish body is covered with dark big spots and fins have dark small spots. Ventral fins, however, are different from these of gobies. While the ventral fins of our gobies form a funnel, the Amur sleeper has two long and thin ventral fins standing clearly apart. Perccottus glenii can grow up to 25 cm in length.

The current accidental findings do not give an overview of the number or range of the Perccottus glenii. Therefore, people who catch this species and inform the ichthyologists ( about this are of great help in further monitoring of this species. Individuals caught have to be preserved, for example, in the freezer, until they can be given to ichthyologists. Because of the aforesaid dangers, we would ask people not to let fish that meet the above description go back to water.

It still remains to be determined how this species ended up in Narva reservoir. Research into this matter is already being planned.


Source: Estonian Ministry of the Environment