Reproduction of the Vimba Bream Vimba vimba (Cyprinidae) in the Tsimlyansk Reservoir: Growth and Patterns of Juvenile Migration in Tributaries of the Azov Basin

This study characterizes the location of natural reproduction sites of the vimba bream, the population’s seasonal dynamics in size composition, and the migration and spatial distribution patterns of juveniles during the first 2 years of their life, based on materials collected between 2001 and 2024 in the Tsimlyansk Reservoir and its tributaries and the Medveditsa River. Effective spawning was observed only in the large Medveditsa, Chir, and Ilovlya rivers. In the Chir and Ilovlya rivers, spawning grounds are located over a distance of 100–150 km and, in the Medveditsa River, about 400 km. Spawning begins in late April–early May. The migration of young of the year from the spawning rivers to the Don River and the Tsimlyansk Reservoir begins in late September–October and can last up to a year. The growth of juveniles in the watercourses of the native (Azov basin) and acquired (Caspian basin) ranges is similar. The sizes of young of the year in September do not exceed 50 mm. The delay in migration of yearlings and 2-year-olds in the spawning rivers Ilovlya and Medveditsa is apparently due to poor nutrition and low growth rates, conditioned by the reduced availability of feeding areas during low-water years.