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For the period 2019-2021, an ecoparasitological study of six fish species - grass carp (Ctenopharyngodon idella Valenciennes, 1844); silver carp (Hypophthalmichthys molitrix Valenciennes, 1844); pumpkinseed (Lepomis gibbosus Linnaeus, 1758); Prussian carp (Carassius gibelio Bloch, 1782); gudgeon (Gobio gobio Linnaeus, 1758); European bitterling (Rhodeus amarus Bloch, 1782) was conducted. The fish were caught from 3 biotopes (Koshava, Kudelin, Novo selo) from the upper section of the Danube River in Bulgaria. A total of two parasite species (Pomphorhynchus laevis Zoega in Müller, 1776) Porta, 1908 and Contracaecum sp. (larvae) were found in two of the investigated fish species. Four fish species were not infected. The ecological indices (mean intensity; mean abundance; prevalence) of parasites were calculated. Kudelin and Koshava biotopes are new habitats for the found helminth species of the infected fish species. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine the relationships between total length and weight (L - W), to estimate the growth parameters (von Bertalanffy) L∞, k, and the mortality rates (Z, M, F) for the common carp (Cyprinus carpio, Linneaus, 1758) and Prussian carp (Carassius gibelio, Bloch, 1782). Sampling was carried out monthly, from March to September 2021. The relationship between length - weight (L - W) in the study period for common carp was W=0.0574×Lt2.6437, respectively W=0.0391× Lt2.7831 for Prussian carp. The growth parameters for common carp were L∞=86.10 cm and K = 0.87 per year, respectively L∞= 40.95 cm and K 0.67 per year, for Prussian carp. The total (Z), natural (M) and fishing (F) mortality rates were 1.47, 0.82 and 0.65 per year, for common carp, respectively Z=1.65, M=0.85 and F=0.80 for Prussian carp. Regarding the exploitation rate (E) this was 0.44 for the common carp population, respectively 0.48 for Prussian carp, suggesting that both fish population were not in over-exploited condition. [ABSTRACT FROM AUTHOR]