The article analyzes the data of long-term studies of sterlet growth in the Kuibyshev Reservoir (watershed of the Volga River) conducted by researchers of the Tatar branch of the All-Russian Research Institute of Fisheries and Oceanography. Significant variations in sterlet length were found not only from year to year, but also in different parts of the reservoir. There have been stated the changes in sterlet population. In recent years, the reservoir has seen an improvement in the growth of sterlet yearlings in comparison with that of fish in the Volga river and in the first years of the reservoir's existence, and a decrease in the growth rate and size of older individuals. It has been found that starlet species in Kama Reaches grow better than in other parts of the reservoir. Fish with fast linear growth is found to increase its percentage, while the part of slow-growing fish decreases.

The article provides a description of the complex pneumatic fish protection structure (FCS) of the pumping station No. 1 of the Karmanovskaya GRES. Estimated design flow rate of NS No. 1 of water intake is 44 m3/s. The RGU includes an impenetrable screen in the form of a zapan, covering the surface two-meter layer of the water intake flow and a pneumatic (water-air) curtain that provides protection for fish fry of various sizes living in the thickness, surface and bottom layers of the reservoir. Ichthyological studies conducted by the Tatar branch of the Federal State Budgetary Scientific Institution "VNIRO" showed that the complex pneumatic fish protection structure protects juvenile fish living in the reservoir with an average efficiency of 86.51%, which exceeds the regulatory requirements of 70% of the current SP 101.13330.2012 (updated edition of SNiP 2.06.07 -87 "Retaining walls, shipping locks, fish passage and fish protection structures" (as amended No. 1).

The article presents a review of the main commercial fish stocks of the Kuibyshev Reservoir based on the long-term research data (2000–2019). The Kuibyshev Reservoir is the leading fishery reservoir in the Republic of Tatarstan, Mari El, Chuvashia, Ulyanovsk and Samara Re-gions. There have been given the data of regular observing species, sex, size-weight and age composition of fish, their reproduction efficiency, distribution, abundance and reproduction of aquatic biological resources, their habitat, as well as control over their fishing and conservation. The analysis of the influence of environmental factors (level and temperature regimes) and fishing on the fish stocks formation is presented. Based on the presented materials, there have been shown the data about the stocks of the main commercial fish species of the Kuibyshev Reservoir (bream, zander, pike, carp, catfish, sterlet) and of the small-sized ordinary fish stocks, the optimal development of which will bring the catches up to 10 thousand tons and more. It has been inferred that for rational fishing in the reservoir, it is necessary to develop a strategy for the integrated effective development of biological resources of the reservoir on an ecosystem basis for better use of the bioproduction capabilities of its biological resources.

Fish production in closed systems is an intensive way of fish farming. However, keeping fish in plants with a closed water supply does not solve the problem of diseases in aquaculture facilities. The greatest damage is caused by bacterial diseases. In this regard, the study of the sanitary state of the aquatic environment of fish is relevant. The article provides information on the physicochemical parameters of water, the species composition of the microflora of the aquatic environment in the basin, microbiological indicators of the sanitary state of water, the total microbial count (TMC) and the number of bacteria of the E. coli group (BCGC) in the RAS when growing rainbow trout. Sanitary indicators of water quality in the pool, both in the first days of keeping rainbow trout, and after a week were within the normal range. There was only a numerical increase in the total microbial number and bacteria of the E. coli group in water samples taken after a week of finding the trout in the pools. According to the results of a study of the contamination of the skin and gills of rainbow trout, as well as the water in which it is contained, an increase in time was revealed from 69 to 73 CFU/ml on the skin and from 85 to 89 CFU/ml on the gills within a week. The qualitative composition of the microflora of the skin and gills of rainbow trout is represented by bacteria of the genera Aeromonas, Pseudomonas, Bacillus, Enterobacter, which is similar to the qualitative composition of the microflora of water. The study of the intestinal microflora of rainbow trout revealed that it also contains bacteria of the genera Aeromonas, Pseudomonas, Bacillus, Enterobacter. At the same time, lactic acid, streptococcal, staphylococcal bacteria, yeast-like fungi of the genus Candida were found, which are normal representatives of the intestinal microflora in small quantities.