In water reservoirs, the size and characteristics of fish, in the first place, affect – the composition and clarity of food objects, the number of food competitors and predators, their numbers, industry, and others. Besides, the rate of linear and weight growth are the arteries that determine the value of the species as an object of commercial fishing. The hybrid of silver and bighead carp easily adapts to different growing conditions (from the point of view of the formation of fish-biological indicators), protein in different years depending on feeding conditions, in one reservoir indicators of length and body weight of ribs are inadequate. Evaluating the influence of feeding conditions on the linear growth of the rib, the method of generalized evaluation was used. An indicator equal to the sum of potential fish productivity for phyto-zooplankton was used to characterize the foraging status of a particular condition in a certain period. In terms of the quality of growth indicators, the indicator of the absolute weight of nature with differentiation of farms, age groups, and years was used. The results of the research revealed significant variability in the size and weight characteristics of different groups of silver and bighead carp, which were isolated from ponds and reservoirs. According to the results of experimental studies established for the cultivation of hybrid silver and bighead carp in reservoirs, relatively high rates of linear and weight growth are expected, higher than for similar species, which is provided in the conditions of fish ponds.

No abstract

Zooplankton plays an important role in aquatic food webs and changes in its abundance and diversity under changing climatic conditions can significantly affect the abundance and diversity of other aquatic organisms. The aim of the study was to assess quantitative and qualitative parameters of zooplankton development, dynamics of development of its dominant groups and the effect of water temperature. Species composition and abundance of zooplankton of the Kremenchuk Reservoir were studied in 2006, 2010–2012 and 2020 in relation to water temperature and pollution. Zooplankton species diversity fluctuated significantly over the years of the study. A total of 46 taxa were recorded in the reservoir during the study period. The number of recorded zooplankton taxa ranged 26 to 32 depending on the year. The most abundant zooplankters were Chydorus sphaericus, Copepoda nauplii, Brachionus diversicornis. The abundance of zooplankters in the reservoir during the study period ranged 23·103 to 256·103 ind./m3, and biomass 0.14 to 0.89 g/m3. A significant positive relationship was observed between the abundance of cladocerans, including some individual species (Ch. sphaericus and Ceriodaphnia sp.), and water temperature. Indicator species of water pollution in different years and in different parts of the Kremenchuk Reservoir differed significantly, which probably depended on the presence or absence (in a certain period of time) of polluting discharges. The total saprobity index in different years in different parts of the reservoir was in the range of 1.5–1.9. Structural indicators of zooplankton and its dominant complexes characterize the water in the Kremenchuk Reservoir as β-mesosaprobic. It is probably too early to assess the impact of climate change zooplankton as these changes are still unstable and short in time, but it is necessary to constantly monitor the biota of aquatic ecosystems to further study and summarize the data, which could later allow an identification of such changes.

Досліджено особливості сумарного вмісту білка, ліпідів та глікогену в органах і тканинах судака Кременчуцького водосховища у переднерестовий на нагульний періоди. У переднерестовий період зареєстровано значно менший вміст сумарних ліпідів у печінці порівняно з нагульним періодом, але значно більший вміст глікогену. Проте наявні енергетичні ресурси організму, на наш погляд, достатні для забезпечення пластичного та генеративного обміну, пов’язаного з трофоплазматичним ростом ооцитів напередодні початку нересту. Отримані результати можуть свідчити про оптимальні екологічні умови і достатній рівень розвитку кормових об’єктів у водному середовищі Кременчуцького водосховища, які забезпечують високий рівень перебігу метаболічних процесів в організмі статевозрілих особин судака у нагульний та переднерестовий періоди річного циклу.

Modern dynamics of the main abiotic environmental factors responsible for fish fauna effective reproduction in the Kremenchuk Reservoir are discussed in the paper. Annual dynamics of water level and temperature were analyzed. It has been found that the main factor responsible for the rate of breeding stock maturation in the Kremenchuk Reservoir is water temperature dynamics rather than spawning temperatures. It is underlined that the operation of hydroelectric facilities and the spawning campaign must be synchronized to ensure sustainable fisheries. The drainage of spawning grounds in low-water years results in the decrease in their area and, as a consequence, in the formation of low-yielding generations. It is recommended to optimize the annual dynamics of water level according to the needs of fisheries.