Dynamics of the age composition and reproductive potential of the Zhaiyk river roach: analysis for the period 2020-2024

The article examines changes in the age structure and reproductive potential of the roach (Rutilus rutilus caspicus) in the Ural River (Zhaiyk) over a five-year period from 2020 to 2024. Based on field observations and fishery catches, an analysis was carried out of the distribution of age groups, sex ratio, average fecundity, morphometric characteristics, and the condition factor of the population. It was found that during the study years, the spawning stock was predominantly formed by individuals aged 3–5 years. In 2024, an increase in the proportion of 5-year-old fish and a temporary rise in the mean age to 4.1 years were recorded, which may reflect the successful survival of cohorts from previous years.

The average individual fecundity ranged from 23.6 to 38.9 thousand eggs, showing a decreasing trend in 2024. Nevertheless, the numerical predominance of young and middle-aged fish maintains the reproductive potential of the population at a stable level. The sex composition was characterized by a strong dominance of females (up to 97.2% in some years), which enhances the reproductive capacity of the species.

The findings indicate that the population of the roach in the Ural River retains ecological stability under conditions of anthropogenic impact and changing hydrological factors, while also emphasizing the importance of regular monitoring of its biological characteristics to ensure sustainable management of the fish resources in the Ural-Caspian basin.

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