FEATURES OF THE HYDROBIOLOGICAL REGIME AND STRUCTURE OF ICHTHY-OFAUNA LAKES KARTAL AND KAGUL IN THE CONDITIONS OF FISHERIES USE OF RESERVOIRS

Abstract

The results of hydrobiological monitoring of Danube lakes (Kagul and Kartal) are given. These lakes are currently used as reservoirs for growing commercial fish. For the study of phytoplankton, zooplankton, macrozoobentos and ichthyofauna, the material was collected in March, July and October 2019. The similarity of the species composition of phytoplankton between the two lakes was high, in March it was 73,0 % (according to the Serensen’s index), in July and October – 59,0 % and 86,0 % respectively. Quantitative indicators of phytoplankton of oz. Kagul and Kartal were almost no different in March and October. In July, biomass of fodder phytoplankton in oz. Kartal was an order of magnitude higher at 5303,676±2713,636 mg·m–3 than Kagul's 417,362±52,409 mg·m–3. The richest taxonomic composition of zooplankton was noted in July (16 taxa), the poorest was in October (8 taxa). In both lakes, the basis of the number and biomass of zooplankton was formed by Rotatoria and Copepoda. In the spring, the greater average biomass of fodder zooplankton (863,58±593,25 mg·m–3) is noted in the oz. Kartal, in summer and autumn was in oz. Kagul 8152,58±2257,41 mg·m–3 and 5609,25±1995,85 mg·m–3 respectively. As part of the macrozoobentos of the studied lakes, oligohetes and two-winged insects were the most massive. The average biomass of fodder benthos in the oz. Kagul (13,816 g∙m–2) was 2,2 times larger than in oz. Kartal (6,386 g∙m–2). Its basis (89,7 % in Kagul, 99,8 % in Kartal) was formed by oligohetes and larvae of two-winged insects. The species diversity of Lake Kartal fish in 2019 was represented by 32 species of fish. 4 species from this list are invasion species: amur chebachok, silver crucian carp, sunny fish, rotan head. It is established that a significant biomass of small short-cyclic species of fish in the lake is not mastered. In these conditions, the stocking of the lake by large aboriginal predators can have a good positive effect, since there is a significant unused fodder base in the reservoir.