Spatial distribution of picoseston in the Saratov reservoir in summer

The structure and spatial distribution of picoseston in the Saratov reservoir in July 2011 and August 2014 are described. On average, the total abundance of cells and particles forming picoseston was 1.87±0.73×106 cells (part.)/mL; and the total biomass of picoseston was 43.8±19.4 µg C/L. During the study period, solitary heterotrophic bacteria and phototrophic picocyanobacteria prevailed in the picoseston of the Saratov reservoir, amounting to 77–100% of its total abundance and biomass. The proportion of picodetrital particles was extremely small (on average, 4.1% of the total biomass of picoseston). The high heterogeneity of picoceston distribution (Cv is 130% and 110% for abundance and biomass, respectively) was found in the Saratov reservoir during the study period. On average, the abundance and biomass of heterotrophic bacterioplaknton and picodetritus at stations of the tributary estuaries were slightly higher than in the riverbed. At the same time, the abundance of picocyanobacteria was higher, and the biomass was lower at the estuarine stations compared to the riverbed ones. The total number of bacterioplankton and autotrophic picoplankton in the Saratov reservoir in 2011 and 2014 corresponded to the mesotrophic level of productivity. Picodetrital particles, in contrast to the Upper Volga and Kama reservoirs, make no significant contribution to the planktonic food webs of the Saratov reservoir, at least during the study period.

The composition of the leukocytes of the bream of the Saratov reservoir

The composition of leukocytes reflects the species and ecological characteristics of fish, while the ratio of individual cell types reflects the functional state of the organism and the nature of the influence of biotic and abiotic stress factors. The work is devoted to the issues of hematopoiesis of the bream Abramis brama — one of the main commercial species of the Volga. The fish were caught in September 2019 at the Saratov Reservoir during a complex hydrobiological expedition aboard the Akademik Topchiev research vessel of the IBIW RAS. In total, 18 sexually mature bream were examined, caught at 3 standard trawling stations: 1 — Shirokiy Buerak, 2 — Khvalynsk, 3 — Kashpir-Rudnik. In fish, peripheral blood was sampled from the tail vein and tissues of the spleen and head kidney. Blood smears and organ imprint smears were performed for the study. The preparations were examined under a light microscope and the leukocyte formula was determined. To determine the index of the abundance of leukocytes in a peripheral blood smear, 100 visual fields were examined at different sites. The leukocyte abundance index allows the intensity of leukopoiesis to be recorded and indirectly assesses the leukocyte level in a blood volume unit. The results of the study showed that lymphocytes predominate in the leukocyte formula, a significant part are blast forms and a small percentage of granulocytes and monocytes/macrophages. The established differences depended on the structural and functional features of the organs: in the kidneys, as the main organ of hematopoiesisin teleost fish, a higher content of blast forms of cells, granulocytes and macrophages was noted, and in the spleen, which serves as a “depot” of blood, lymphocytes and macrophages. Blood, as an integral system, bears all types of cells circulating in the immune system at the moment. The intensity of leukopoiesis was higher in fish from the upper part of the reservoir.