Changes in the Diet of the Zander Sander lucioperca (Percidae) in the Kama Reservoir as a Result of Invasion of an Alien Species the Black and Caspian Sea Sprat Clupeonella cultriventris (Ehiravidae)

In the modern period, the role of native species, the roach Rutilus rutilus and perch Perca fluviatilis, has significantly decreased in the diet of the zander Sander lucioperca in the Kama Reservoir in comparison with the retrospective data, and their place has been taken by the Black and Caspian Sea sprat Clupeonella cultriventris, which was most intensively fed by zander in August and September. The occurrence of Black and Caspian Sea sprat in stomachs of zander was lower in May and especially in October, which may be related to the dynamics of its abundance and seasonal movements in the reservoir. Juvenile zander with a standard length of less than 40 cm is characterized by a decrease in the average body length of the consumed sprat with an increase in the size of the predator, whereas the opposite was found for adult individuals. This dependence can be explained by a high feeding rate of zander juveniles and low selectivity of this group of fish when hunting for sprat, as well as by the dynamics of the size composition of sprat in the reservoir. Black and Caspian Sea sprat is currently the dominant food object of zander in the Kama Reservoir.