Fisheries characteristics and stock assessment of the Prussian Carp (Carassius gibelio Bloch, 1782) in the Zaporizke (Dnipro) reservoir

The article provides a detailed fisheries assessment of the Prussian carp (Carassius gibelio Bloch, 1782) population in the Zaporizke (Dnipro) Reservoir, based on long-term hydrobiological and ichthyological monitoring conducted between 2016 and 2024. The primary objective was to evaluate the current state of the species’ commercial stocks, examine spatial differentiation in biological indicators, and determine optimal harvesting volumes under varying environmental conditions. Fieldwork was conducted in several areas of the reservoir with different levels of anthropogenic pressure, including the central part, the lower section, and the ecologically strained Samara Bay. The results of control and commercial catches confirm that Prussian carp is the dominant fish species in the reservoir's ichthyofauna and exhibits stable natural reproduction. Biometric parameters of four-year-old individuals – such as body length, weight, and condition factors (Fulton and Clark) – demonstrated significant spatial variation. Fish from Samara Bay were found to be smaller and in poorer condition compared to individuals from cleaner areas, which is likely a result of chronic pollution, high population density, and limited food resources. The dynamics of young-of-the-year fish abundance and biomass were analyzed, revealing consistent recruitment across multiple years. Young-of-the-year density remained relatively high, especially in Samara Bay, which serves as a key spawning and nursery habitat. The total commercial stock of Prussian carp was estimated at 6.020 tonnes, with a recommended annual catch limit of 1.500 tonnes, including allocations for scientific research. The findings highlight the adaptive capacity of this invasive species and its growing role in reservoir fisheries. The results are important for the development of sustainable fisheries management strategies, regulation of catch intensity, and planning of bioremediation and stock control measures in large regulated water bodies.