The Tobol River, a nationally significant economic water body, serves various purposes and spans across diverse landscape zones and environmental conditions. An evaluation of the forage base development of the Tobol River was conducted through the survey of six stations along the river in 2019. The investigation revealed a total of 15 species of planktonic invertebrates, including 6 rotifers, 5 cladocerans, and 4 copepods, as well as 28 species of benthic organisms. The survey period of 2016-2019 registered 36 species and forms of benthic organisms within the Tobol River basin, with a high diversity of insect groups. The considerable length and varied landscape zones of the river contribute to the observed high diversity of organisms. In terms of zooplankton development, the Tobol River exhibits a moderate food supply class and, according to S.P. Kitayev's trophic scale, can be classified as a β-mesotrophic water body. Similarly, the river's zoobenthos development indicates a moderate food supply class, designating it as an αmesotrophic type under S.P. Kitayev's trophic classification. The study of the food spectrum of river perch and roach in the Tobol River suggests relatively high food availability for these species, underscoring the importance of understanding the ecological and biological forage base of the river for maintaining ecosystem health.

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In this article, the study and prediction of the state of fish resources in the Yesil River was carried out to determine the boundary reference points of the reserve and management decisions in case they are exceeded, to ensure sustainable fisheries and preserve biological diversity. Ichthyological studies, retrospective analyses and rankings of the effects of the water supply of the Yesil River on fish stocks have been carried out, critical values ​​of the biomass of fishing reserves have been determined, as criteria for biologically safe fishing values and targets for management of fish stocks at reaching the boundary values ​​of 24.03 tonnes have been established. According to the results of studies of basic biological indicators, it was determined that roach, bream, pike and perch populations each had an LC50 above LM50, which indicates their low utilization in the fishery industry. A strategy for management of fish stocks, recommendations for the conservation of fishery resources and their rational use has been developed as a result of these findings. The list and status of the monitored indicators for the careful management of fish stocks, as well as a list and indicators of the boundary indicators for the state of fish stocks, was established. These parameters included the fish size of 50% of the sampled fish and 50% of maturity achieved, where the LC50 was observed in the fish in question from 19 to 45.4 cm and LM50 from 12.3 to 41 cm, respectively. The minimum and maximum river levels that ranged from 111 up to 159 cm, as well as the critical value of the commercial reserve, corresponded to the boundary value of 24.03 tonnes. The results of this work will serve as the basis for making future managerial decisions, necessary for sustainable fisheries and conservation of the biological diversity of the Yesil River.