Cladocera belonging to Chydoridae, Sididae, and Macrothricidae families constitute the essential part of the inshore fauna of the Volga Water Reservoirs . They play an important role in the food of fishes and attract attention as possible objects of cultivation as live feed for fishes . Due to integuments persisting in the sediments Chydoridae serve as the indicators of the past conditions of water bodies (FREY 1958, 1959, 1961, KORDE 1960) . According to the plan of ecological work on these Cladocera (SMIRNOV 1961(SMIRNOV , 1962(SMIRNOV , 1962a) ) the material was collected giving the possibility of surveying their distribution in the Volga Water Reservoirs and their abundance on the various grounds and vegetation beds .
696 quantitative samples from 185 stations from the Ivankovo Water Reservoir to the Volga Delta were collected . The material from the Ivankovo Water Reservoir to the Gorkiy Water Reservoir was collected in 1953-1961, the material below the city of Gorkiy was collected in 1961 . Some qualitative material from the Perm Water Reservoir for August 1961 was also used .
The samples in the seasonal aspect were collected in the southernpart of the Rybinsk Water Reservoir at Borok . The maximum abundance of Chydoridae is observed from the middle of July to September . Accordingly the Volga Water Reservoirs were investigated during this period of maximum abundance .
The samples were taken in the inshore zone less 1 m deep using the vegetation sampler by V . I . BUT, the tubular bottom sampler by F. D . MORDUKHAY-BOLTOVSKOY after the techniques described by F. D . MORDUKHAY-BOLTOVSKOY (1955, 1958) . On sand where the tubular bottom sampler was inefficient the samples were taken with