The role of the long-toed crayfish (Pontastacus leptodactylus leptodactylus) in the hydrocenosis of a water body in the floodplain of the Rutka River, one of the tributaries of the Middle Volga, was studied in order to determine an ecologically grounded catch rate. During the study period, the population of P. l. leptodactylus had a high productivity and occupied the dominant status in the biocenosis among the components of animal origin. The amount of plant biomass consumption in summer by juveniles and sexually mature crayfish was calculated. Zoobenthos is consumed in relatively small quantities by all age groups of the crayfish population; zooplankton – by underyearlings. The consumption of aquatic vegetation by crayfish determines the importance of their role in restraining its growth and in limiting the eutrophication of the water body. The biomass of the P. l. leptodactylus population was calculated. It must always be present in the water body to maintain the stability of its biocenosis, which is possible if the annual catch of crayfish is limited to 10-15% of their commercial stock.