Biological characteristic of the bream Abramis brama L. in the Dnieper-Bug mouth region

Abstract

The effective functioning and development of the fishing industry of Ukraine in the economic space is determined not only by quantitative indicators, but also by the peculiarities of the formed economic relations at the end of the last - the beginning of the present century. The basis of the raw material base of the fishing industry of Ukraine, including the Kherson region, at the end of the 20th century was formed mainly due to catches of fish and seafood and, to a lesser extent, the products of intensive fish farming. At the same time, the fisheries of the Kherson region over the past decade have seen a steady decline in production and processes of reducing its potential, including the aging of the technical base, increasing resource and financial imbalances, leading to a decline in production. The situation is exacerbated by the increasing anthropogenic pressure on aquatic ecosystems, which has caused a sharp decline in fish catches of major industrial categories, additionally a few rare species have disappeared from industrial statistics. Natural fish populations adequately respond to the situation through adaptive reactions in the form of changes in the nature of ichthyologic mass formation, age structure, in productive indicators of species. These studies highlight the issue of the state of productive capabilities of the local herd of bream of the Dnieper-Bug estuary. The initial data for the tasks are the results of field research conducted during 2014-2018 within the waters of the Dnieper-Bug estuary within the research of the Educational and Scientific Laboratory "Prospects of Aquaculture" of the Kherson State Agrarian and Economic University. Abramis brama L. bream of different ages were selected as the object of research. The analysis of the productive abilities of female bream showed a depressed state of the population within the water area, which was the place of research. Absolute individual fertility of female bream depending on age ranged from 86.62 to 288.69 thousand eggs, its minimum value was observed for 4-year-old females with an average body length of 30.5 cm and a weight of 647.5 g, the maximum value for 11-year-old females with a length of body weight 48.9 cm and weight 2047.1 g. At the same time for five years of observations the fertility of female bream in some age groups decreased by 8.2–12.8%. On the other hand, in comparison with the last century, the value of the absolute individual fertility of female bream in all age groups has decreased by 6.1–28.2%. At the same time, a significant difference in the amount of fertility was observed in both juvenile females and females of the oldest age, which clearly indicates the deterioration of the reproductive abilities of the herd due to increased anthropogenic pressure on the bream population. The research results significantly deepen the data on the current biological state of the industrial herd of bream of the Dnieper-Bug estuary.