New Data on the Population of Dreissena polymorpha (Pallas, 1771) (Bivalvia, Dreissenidae) in the Vyatka River (Volga River Basin)

This is the first record of a self-sustaining population of Dreissena polymorpha from the eastern edge of the invasive range in the middle reaches of the Vyatka River (tributary of the Kama River, basin of the middle reaches of the Volga River). The study considers morphometric and weight parameters of 275 mollusks: specifically, shell length of 21.36 ± 5.49 (3.6–38.8) mm, wet weight with shell 1.14 ± 0.76 (0.01–6.5) g. The shells largely (98%) feature strongly convex sculpture (the convexity index to height J_CH > 0.71). The population includes individuals up to 7 years old. Mollusks with the shell length of 15–30 mm constitute more than 85% of the population. A wide range of variation in size and weight characteristics of mollusks with dominance of medium-sized individuals points to stability of this zebra mussel population on the northeastern periphery of the range.