BIOLOGICAL CHARACTERISTICS OF PRUSSIAN CARP (CARASSIUS AURATUS GIBELIO (BLOCH, 1782)) COMMERCIAL STOCK OF THE DNIEPER-BUG ESTUARY

Purpose. To provide the biological assessment of the silver Prussian carp (Carassius auratus gibelio (Bloch, 1782)) commercial stock of the Dnieper-Bug estuary in the conditions of the transformed Dnieper river flow. Methodology. During the analysis of the biological state of the Prussian carp commercial stock, the main attention was given to the dynamics of age and sexual structure, length-weight growth rate, absolute fecundity and condition factor. The basic data were collected during the work of control-observation stations of the Institute of Fisheries in the Dnieper-Bug estuary during the current century. The collection and processing of ichthyological materials were performed in accordance with the generally accepted methodologies. Findings. The analysis showed that during the current century, the age structure of the Prussian carp of the Dnieper-Bug estuary was the most labile among other commercial cyprinids. It was found that as a result of an increase in the right wing of the age series, there was a gradual increase of the mean weighted age of its commercial stock. At the beginning of studies (2001-2002), the core of the stock was formed by age-3-6 fish (up ); however in subsequent years, a displacement of dominant groups toward the dominance of age-4-7 fish (more than 80% of the total stock) was observed. At the same time, the relative number of age-3 fish (recruits) was at a relatively high level – up to 10.6%. The linear growth varied more intensively until the age-5, but it reduced with ageing and did not show high variability. The body weight most variable was in age-4 fish (Cv=9.62%). The noted insignificant deviations in the body weight growth rate of the right wing of the age series was due to stable predominance of females in the stock structure, which were characterized by a variability of the mean weight as a result of different development of gonads. The dynamics of the age-related changes in the condition factor indicated on a gradual decline Fulton condition factor from 3.47±0.22 in age-3 fish to 3.12±0.06 in age-6 fish. The highest variability of these indexes was typical for age-5 fish (Cv=10.9%; lim=2.46-3.89), that was related to the linear-weight growth and fecundity. With an increase in the age, the variableness of condition factor reduced substantially. Originality. The paper contains modern and significantly updated data on main biological characteristics of the Prussian carp commercial stock in the transformed conditions of the Dnieper-Bug estuary. Practical value. The obtained results are a scientific background for rational fishery optimization of commercial pressure on the representatives of valuable fish fauna of the Dnieper-Bug estuary. In current conditions, the presented information is actual enough from the point of view of the maintenance and support the biodiversity of valuable commercial species in natural water bodies of Ukraine.