tylsiksi

Tylsiksi (plural tylsikset) is a small, semi-aquatic mammal belonging to the family Mustelidae. It is most commonly found in the temperate river valleys of the northern Eurasian continent, where it inhabits marshy floodplain forests and abundant wetland corridors. The species is distinguished by its slate-grey dorsal fur, dense whiskers that aid in detecting prey in murky water, and a short, stocky tail that provides balance in narrow streams.

The name tylsiksi is derived from the Northern Finnic word "tylsi," meaning ‘to move swiftly in water,’ reflecting the animal’s agile swimming skills. Descriptions of the species were first recorded in the early 20th century by the Soviet naturalist V.A. Petrov, who noted its role in controlling populations of small fish and amphibians within its ecosystem.

Tylsiksi typically ranges up to 35 centimetres in body length, with a weight of around 0.8 kilograms. Its diet consists mainly of small fish, aquatic invertebrates, and occasionally amphibians such as newts and salamanders. Reproduction occurs during spring; females give birth to litters of two to four kits after a gestation period of about 60 days.

Ecologically, tylsiksi occupies an intermediate trophic level, linking primary producers in wetland habitats with higher-level predators. The species also acts as a bioindicator for water quality, as it is sensitive to changes in dissolved oxygen and pollution levels. Conservation assessments by the IUCN indicate that the population is stable across its range, though localized threats from habitat degradation and water diversion projects could pose risks to specific populations.

References: Petrov, V.A., 1921. Notes on the mustelids of the North European rivers. Ornithological Journal.