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.

The regulation of the flow of the Volga River by the Zhigulevskaya HPS has changed the living conditions for many fish species. At the same time, the pelagial was a completely new type of biotope for the fish population. The fish population of the Kuibyshev reservoir, newly formed in the pelagial, began to have certain features inherent in this biotope. Currently, according to the results of four years of research, 18 species of fish have been noted here, belonging to 5 families, the basis of which are five species - kilka, sabrefish, bleak, pike perch and bream. It was revealed that the Volga part of the reservoir is more productive than the Kama part, and pelagic fish communities have a certain vertical distribution and migration through the water column, mainly occupying the biomass accumulation zone. The absence of a fishing fleet and the trend in the development of fishing on the reservoir casts doubt on the further rational use of aquatic biological resources in this ecological zone of the Kuibyshev reservoir.

The results of six-year observations (2012-2017) in the Meshinsky Gulf of the Kuibyshev reservoir concerning the evaluation of the reproduction efficiency of the main commercial fish of this section of the reservoir have been reviewed and analyzed. Data are given on the species composition of prolarvae and larvae of fish in the coastal part of the reservoir. It has been established that the most abundant in the studied years was the fry of roach, bream and silver bream; the larvae of carp and ruff were least common in catches. A method for estimating yields by catches of fish larvae based on deviations in the mean value of the catch has been proposed. According to these data, in 2012-2017 there was one high-yielding generation, in the remaining years - medium-yielding. It is shown that the dynamics of the number of fish larvae in the coastal region depends on the course of spawning and obeys the normal distribution in time. Analysis of the relative indices of the quantity of larvae - pieces/catches and pieces/1m of the coastal area in the studied years has been given. A method is described for calculating the absolute abundance of fish larvae in the littoral by the example of the Meshinsky Gulf. According to calculated data, the average number of early juveniles in the littoral of the Meshinsky Gulf in 2012-2017 was about 4 billion specimens, which corresponds to the figures obtained in previous years in the Sviyazhsky Gulf of the Kuibyshev Reservoir. The study results have great practical importance and can serve as data for prediction of catches and determining the state of ecological system of the reservoir.