Changes in biological indicators of the silver bream Blicca bjoerkna at the upper part of the Volga stretch of the Kuybyshev reservoir in connection with the anthropogenic impact

In recent years, the silver bream of the upper part of the Volga stretch of the Kuibyshev reservoir maintained a tendency to reduce the average size and weight indicators. Given the good availability of food and the fact that in the area under consideration, commercial fishing of this species has not been carried out in recent years, it can be assumed that changes in biological indicators are caused by a significant impact of anthropogenic impact in the form of individual and poaching fishing. It is necessary to strengthen control measures for such types of fishing

Basic biological parameters of white-eye bream Abramis Sapa

© 2020, Advanced Scientific Research. All rights reserved. Of the goal of this study is to investigate the structure and basic biological parameters of white-eye bream Abramis sapa (Pallas, 1814), which give the information about the state of population of this specie in the conditions of Sviyaga Bay of the Kuibyshev Reservoir. The parameters such as gender, size and age structure of white-eye bream were considered, on the basis of the control catches, obtained as a result of trap-net fishing in 2013-2017. Based on the investigation the male/female ratio was 1:1, with some predominance of females in certain years. Weight and dimensional parameters varied over years and were slightly lower than in the previous periods of study. The observed trend towards a certain decrease in the size of white-eye bream may be associated with the presence and availability of food supply, its composition. White-eye bream females have larger sizes and greater body mass than males, and due to this, they can successfully compete for food with main competitors. Moreover, the females are able to avoid pressure of juvenile fish of predatory species. The age structure shows relatively unstable state of the white-eye bream population in the reservoir. The age structure of white-eye bream in the period 2013-2017 was represented by 2-9 years-old fish. The age of most fish ranged from 4 to 5 years; 8-9 years-old fish were noted only in some years and comprised from 3 to 6% of the control catches. The index of Fulton's condition factor to a greater extent reflects the physiological state, first of all, the degree of maturity of reproductive products and the degree of fish feeding, i.e. the amount of food in the digestive tract