Successful establishment of the Asian cyclopoid copepod Thermocyclops taihokuensis in Ukrainian waters

Thermocyclops taihokuensis (Harada, 1931) was recorded for the first time in Ukraine (Kyiv region). The species was found in the Bucha River and the Sovki River in 2020, and from 2021 to 2025 it was continuously present in high numbers and was the dominant zooplankton taxon in the warm seasons in Nyvky Park pond (Syrets River), indicating successful establishment of this Asian Thermocyclops species in the ponds of the right-bank tributaries of the Dnieper River. Of the three species of the genus native to Ukraine, Thermocyclops oithonoides (Sars G.O., 1863) is most similar to T. taihokuensis morphologically. Distinguishing features between the Asian Thermocyclops and native congeners, as well as the ecology of T. taihokuensis in its native range, are discussed. No native Thermocyclops species co-occurred with T. taihokuensis in the studied water bodies, which may indicate competitive replacement of the local species by the new non-native invasive one.